ANSWER: B

Rationale:

Option B is correct. Tenecteplase is an appropriate and increasingly preferred fibrinolytic for STEMI at facilities without timely PCI access. It is dosed as a single weight-based IV bolus administered over 5 to 10 seconds: 30 mg for less than 60 kg, 35 mg for 60 to less than 70 kg, 40 mg for 70 to less than 80 kg, 45 mg for 80 to less than 90 kg, and 50 mg for 90 kg or above. For this 82 kg patient, the correct dose is 45 mg. Tenecteplase's three engineering modifications — T103N/N117Q (extended half-life of approximately 20 to 24 minutes, enabling single-bolus dosing) and KHRR→AAAA (14-fold greater PAI-1 resistance) — make it pharmacologically advantageous at platelet-rich arterial thrombi and logistically practical in community settings. The ASSENT-2 trial demonstrated non-inferiority to alteplase for 30-day mortality with less non-cerebral bleeding.

• Option A: Option A is incorrect: streptokinase is a reasonable historical agent but is not preferred over fibrin-specific agents in current practice; its non-fibrin-specific mechanism produces a systemic lytic state with higher major bleeding risk; "more complete clot dissolution" with non-fibrin-specific agents is not an established advantage and is pharmacologically misleading.
• Option C: Option C is incorrect: the accelerated 90-minute alteplase protocol is the correct regimen for alteplase in STEMI, but the claim that alteplase is the only agent with STEMI mortality evidence is false — tenecteplase demonstrated non-inferiority in ASSENT-2 and is guideline-endorsed for STEMI fibrinolysis.
• Option D: Option D is incorrect: the reteplase protocol is two fixed 10-unit IV boluses given 30 minutes apart, unconditionally — there is no conditional second bolus; adapting the second bolus to ST resolution is not the approved or studied reteplase protocol.

ANSWER: C

Rationale:

Option C is correct. Post-fibrinolysis anticoagulation in STEMI is required to prevent reocclusion and support the pharmacoinvasive strategy (planned coronary angiography at 3 to 24 hours). Enoxaparin is preferred over UFH based on the ExTRACT-TIMI 25 trial, which demonstrated significantly reduced 30-day death or nonfatal MI with enoxaparin versus UFH in post-fibrinolysis STEMI patients. The standard dosing for patients under 75 years with CrCl above 30 mL/min is a 30 mg IV bolus followed by 1 mg/kg SC every 12 hours; for this 82 kg patient that is 82 mg SC every 12 hours after the bolus. Anticoagulation must continue for a minimum of 48 hours or until revascularization.

• Option A: Option A is incorrect: UFH is an acceptable alternative when enoxaparin is unavailable or contraindicated, but it is not the preferred agent — ExTRACT-TIMI 25 established enoxaparin superiority; the rationale that protamine reversibility makes UFH preferred in the post-thrombolytic period is not guideline-supported.
• Option B: Option B is incorrect: fondaparinux 2.5 mg SC once daily is an alternative for patients managed with a non-invasive strategy, but it is not preferred over enoxaparin for all post-STEMI patients; critically, fondaparinux cannot be used as the sole anticoagulant during PCI — it requires UFH supplementation during catheterization due to catheter thrombosis risk from lack of anti-IIa activity; describing it as universally preferred is incorrect.
• Option D: Option D is incorrect: post-fibrinolysis anticoagulation is mandatory and evidence-based; without anticoagulation, the reocclusion rate after fibrinolysis is unacceptably high — the fibrin-specific mechanism of tenecteplase does not eliminate this risk; antiplatelet therapy alone is insufficient.

ANSWER: A

Rationale:

Option A is correct. The pharmacoinvasive strategy — routine coronary angiography at 3 to 24 hours after fibrinolysis — is recommended regardless of apparent clinical reperfusion success, based on trial evidence (TRANSFER-AMI, CARESS-in-AMI) demonstrating that early angiography and PCI of the infarct-related artery after fibrinolysis reduces recurrent ischemia and reinfarction compared with a purely ischemia-guided approach. The optimal window is 3 to 24 hours after lysis; earlier than 3 hours is not recommended as it does not improve outcomes. Failed fibrinolysis — defined as less than 50% ST-segment resolution at 90 minutes, persistent chest pain, or hemodynamic instability — requires immediate rescue PCI regardless of the elapsed time since fibrinolysis, as continued coronary occlusion carries unacceptable mortality.

• Option B: Option B is incorrect: deferring angiography for 72 hours is not recommended and contradicts the pharmacoinvasive strategy evidence; coronary instrumentation after fibrinolysis is safe in the 3 to 24 hour window; the concern about vessel friability at 24 hours is not supported by clinical evidence and is not a guideline-endorsed reason to delay angiography.
• Option C: Option C is incorrect: the pharmacoinvasive strategy applies to all post-fibrinolysis STEMI patients including those with complete ST resolution; even patients with apparently complete reperfusion benefit from early angiography to characterize the residual stenosis and determine whether PCI is needed to prevent reocclusion.
• Option D: Option D is incorrect: universal rescue PCI at 4 to 6 hours regardless of clinical status would be harmful — early PCI within 3 hours of fibrinolysis (the hyperacute window) is associated with increased bleeding without improved outcomes; rescue PCI is indicated for failed fibrinolysis, not prophylactically for all patients.

ANSWER: D

Rationale:

Option D is correct. Current STEMI guidelines specifically recommend clopidogrel as the P2Y12 inhibitor when fibrinolytic therapy is used, based on the CLARITY-TIMI 28 trial (clopidogrel 300 mg loading + 75 mg daily added to fibrinolysis reduced cardiovascular events) and COMMIT trial evidence. The loading dose is age-stratified: 300 mg for patients under 75 years and 75 mg (no loading dose) for patients 75 years or older, reflecting the increased intracranial hemorrhage risk in elderly patients on combined antithrombotic therapy. Prasugrel and ticagrelor — despite their superior efficacy in PCI-treated ACS — are specifically not recommended in combination with fibrinolysis because their more potent platelet inhibition in the context of active systemic fibrinolysis has not been studied and raises concern for additive intracranial hemorrhage risk; their use is reserved for the post-PCI setting.

• Option A: Option A is incorrect: ticagrelor is not recommended in the fibrinolysis setting; its direct-acting mechanism and more potent platelet inhibition are specifically the reason it is excluded — not an advantage — when combined with a thrombolytic agent.
• Option B: Option B is incorrect: prasugrel's superiority in TRITON-TIMI 38 was demonstrated in the PCI setting, not in fibrinolysis-treated patients; the trial explicitly excluded patients who received fibrinolytic therapy; applying the TRITON-TIMI 38 benefit to fibrinolysis patients is not supported by evidence.
• Option C: Option C is incorrect: DAPT combined with fibrinolytic therapy and anticoagulation is the guideline-recommended approach for post-fibrinolysis STEMI; withholding P2Y12 therapy until angiography is not standard of care and would leave the patient at increased risk for reocclusion during the transfer period.

ANSWER: A

Rationale:

Option A is correct. The pre-treatment BP threshold for alteplase in acute ischemic stroke is 185 mmHg systolic AND 110 mmHg diastolic — both criteria must be met. This patient's systolic BP of 198 mmHg exceeds the 185 mmHg ceiling and must be lowered before alteplase is administered. The AHA/ASA-recommended IV agents are labetalol (10 to 20 mg IV over 1 to 2 minutes, may repeat once) and nicardipine (5 mg/hr IV infusion, titrated up by 2.5 mg/hr every 5 to 15 minutes to a maximum of 15 mg/hr). Once BP is at or below 185/110 mmHg, it must be maintained below 180/105 mmHg for at least 24 hours after alteplase. If BP cannot be reliably brought to and held below 185/110 mmHg, alteplase should not be given.

• Option B: Option B is incorrect: the 185/110 mmHg threshold requires both the systolic AND diastolic to be within limits; with a systolic of 198 mmHg (well above 185 mmHg), the criterion is not met regardless of the diastolic value; this reasoning is pharmacologically and clinically incorrect.
• Option C: Option C is incorrect: while time is critical in acute stroke, administering alteplase above the BP threshold substantially increases the risk of hemorrhagic transformation; the pre-treatment BP target is a safety requirement, not a recommendation — the expected delay for BP management with IV agents is typically 10 to 20 minutes and does not meaningfully offset the treatment window.
• Option D: Option D is incorrect: oral amlodipine has a slow onset of action (hours to days to reach therapeutic effect) and is entirely inappropriate for acute pre-alteplase BP reduction; only IV agents with rapid titrable onset are appropriate in this setting.

ANSWER: D

Rationale:

Option D is correct. The standard alteplase protocol for acute ischemic stroke is 0.9 mg/kg with a maximum total dose of 90 mg. The dose is administered in two parts: 10% given as an IV bolus over 1 minute, and the remaining 90% infused over 60 minutes. For this 68 kg patient: total dose = 0.9 × 68 = 61.2 mg; bolus = 6.12 mg over 1 minute; infusion = 55.08 mg over 60 minutes. After alteplase administration, BP must be maintained below 180/105 mmHg for at least 24 hours to protect the ischemic territory from hemorrhagic transformation. All antithrombotic agents must be held for 24 hours; brain CT or MRI at 24 hours precedes any antithrombotic resumption.

• Option A: Option A is incorrect: 100 mg over 2 hours is the alteplase regimen for massive PE (pulmonary embolism), not for acute ischemic stroke; the post-treatment BP target of 160/90 mmHg is lower than required and would risk reducing cerebral perfusion pressure in the ischemic penumbra, potentially worsening neurological outcomes.
• Option B: Option B is incorrect: the 0.6 mg/kg rapid protocol is used specifically for alteplase in cardiac arrest — it is not a standard dose-reduction protocol for elderly patients; while the ENCHANTED trial evaluated lower-dose alteplase (0.6 mg/kg) in stroke, it did not demonstrate improved safety with maintained efficacy and lower-dose alteplase has not replaced the standard 0.9 mg/kg protocol in major guidelines.
• Option C: Option C is incorrect: the standard protocol divides the dose into a bolus (10%) and a 60-minute infusion (90%); giving the entire dose as a single bolus over 2 minutes is not the approved protocol and would deliver the drug approximately 30 times faster than the standard infusion rate, significantly increasing the risk of hemorrhagic transformation from rapid plasmin generation.

ANSWER: B

Rationale:

Option B is correct. The 24-hour antithrombotic hold after alteplase is now complete, and 24-hour brain imaging has been obtained as required. HI-1 hemorrhagic transformation (minor petechiae without mass effect) is a common imaging finding after ischemic stroke and does not preclude antithrombotic therapy. Aspirin for secondary prevention can be started at 24 hours given the absence of significant hemorrhagic transformation. For patients with atrial fibrillation requiring oral anticoagulation, initiation of anticoagulation after stroke thrombolysis is typically deferred beyond 24 hours: the timing is guided by infarct size and hemorrhagic transformation grade. Current guidelines and expert consensus suggest 4 to 14 days deferral — shorter for small infarcts with no or minimal hemorrhagic transformation, longer for moderate to large infarcts or higher-grade hemorrhagic transformation. For this patient with a moderate infarct and HI-1 pattern, reimaging at 5 to 7 days and initiating apixaban if no hemorrhagic expansion is a reasonable evidence-informed approach.

• Option A: Option A is incorrect: immediate resumption of anticoagulation at 24 hours in a patient with moderate infarct size and any degree of hemorrhagic transformation is not recommended by current guidelines; the 4 to 14 day deferral exists specifically to allow the blood-brain barrier to stabilize and hemorrhagic transformation to mature before introducing anticoagulation.
• Option C: Option C is incorrect: there is no guideline-based 7-day universal hold for all antithrombotics after stroke thrombolysis; aspirin is started at 24 hours in most patients after 24-hour imaging confirms no significant hemorrhagic transformation; only anticoagulation requires extended deferral.
• Option D: Option D is incorrect: HI-1 hemorrhagic transformation does not permanently contraindicate all antithrombotic therapy; this is a minor imaging finding and permanent discontinuation of anticoagulation in a patient with atrial fibrillation would leave her at high long-term risk of cardioembolic stroke.

ANSWER: C

Rationale:

Option C is correct. Acute neurological deterioration during alteplase administration — particularly with pupillary changes suggesting transtentorial herniation — is sICH (symptomatic intracranial hemorrhage) until proven otherwise. The protocol is: (1) stop the alteplase infusion immediately — every additional milliliter of alteplase delivered increases hemorrhage risk; (2) obtain emergent non-contrast CT head — confirm ICH and exclude other causes; (3) draw simultaneous labs — CBC, PT/INR, aPTT, and fibrinogen are essential to characterize the lytic state; fibrinogen below 150 mg/dL confirms systemic plasminemia requiring active replacement; (4) call neurosurgery; (5) if CT confirms ICH and fibrinogen is depleted — cryoprecipitate 10 units IV (target fibrinogen above 150 mg/dL) followed by an antifibrinolytic agent (TXA 10 to 15 mg/kg IV or aminocaproic acid 5 g IV); (6) maintain systolic BP below 180 mmHg to limit hemorrhagic expansion.

• Option A: Option A is incorrect: completing the alteplase infusion during active ICH with herniation would be catastrophic — continuing fibrinolytic delivery while a patient is hemorrhaging and herniating is explicitly contraindicated; the infusion must stop immediately.
• Option B: Option B is incorrect: TXA must not be administered before CT confirmation of ICH — if the neurological deterioration has a non-hemorrhagic cause (severe cerebral edema, seizure), antifibrinolytic therapy could promote thrombotic complications; CT confirmation precedes pharmacological reversal.
• Option D: Option D is incorrect: while cerebral edema can cause deterioration, the timing (40 minutes post-alteplase) does not exclude hemorrhage — sICH can occur at any time during or after alteplase infusion; treating presumed edema with mannitol while continuing to miss a developing ICH would be clinically dangerous; CT must be obtained before any empirical treatment.

ANSWER: C

Rationale:

Option C is correct. For PE-induced cardiac arrest, a modified rapid alteplase protocol is used: 0.6 mg/kg IV (maximum 50 mg) administered over 15 minutes. For this 88 kg patient, 0.6 × 88 = 52.8 mg, capped at 50 mg. This differs from the standard 100 mg over 2-hour PE regimen — the rapid protocol is designed for cardiac arrest where every minute without restoration of pulmonary blood flow is fatal and a 2-hour infusion is clinically impractical. CPR must be continued throughout the infusion and for at least 60 to 90 minutes afterward to allow time for clot dissolution to restore circulation; do not cease resuscitation prematurely after thrombolytic administration. If ROSC (return of spontaneous circulation) is achieved, the patient should be transferred for CT pulmonary angiography and definitive management.

• Option A: Option A is incorrect: the standard 100 mg over 2-hour alteplase regimen is used for hemodynamically unstable massive PE not in cardiac arrest; in cardiac arrest, the 2-hour infusion duration is inappropriate — the rapid 0.6 mg/kg over 15-minute protocol is used.
• Option B: Option B is incorrect: tenecteplase is not FDA-approved for PE treatment; its use in PE-induced cardiac arrest lacks the evidence base and regulatory approval of alteplase; single-bolus convenience does not establish it as preferred in this life-threatening indication.
• Option D: Option D is incorrect: active CPR is a relative contraindication to thrombolysis (not absolute), and in PE-induced cardiac arrest — where the cause is reversible and no other intervention is available in the timeframe needed — thrombolysis is not only permissible but is the recommended pharmacological intervention in current resuscitation guidelines (AHA, ERC); the concern about CPR-related trauma is a relative risk that does not prohibit thrombolysis in this context.

ANSWER: A

Rationale:

Option A is correct. After alteplase administration for PE — including the cardiac arrest protocol — UFH anticoagulation should be resumed without a loading bolus once the aPTT falls to below approximately 80 seconds (or below approximately twice the control value), which typically occurs 2 to 3 hours after completion of the alteplase infusion as the lytic state begins to clear. The bolus is deliberately omitted because the patient remains in a plasmin-mediated lytic state immediately post-alteplase, and adding a full heparin bolus (80 units/kg) would substantially increase bleeding risk including intracranial hemorrhage. The infusion is started and titrated to aPTT 60 to 80 seconds. Subsequent definitive management (CT pulmonary angiography, IVC filter consideration, anticoagulation transition) follows hemodynamic stabilization.

• Option B: Option B is incorrect: a 24-hour anticoagulation hold after alteplase is the protocol for acute ischemic stroke — not for PE; in PE patients, anticoagulation is resumed within hours once the aPTT allows, because the underlying venous thromboembolism requires ongoing treatment to prevent propagation and recurrence.
• Option C: Option C is incorrect: a full 80 units/kg UFH bolus immediately after alteplase would add anticoagulant loading to an already lytic state; the risk of major bleeding including intracranial hemorrhage in this setting is substantial; the post-alteplase protocol explicitly calls for infusion without bolus once the aPTT is below threshold.
• Option D: Option D is incorrect: oral anticoagulants including DOACs (direct oral anticoagulants) are inappropriate in the acute post-arrest ICU setting; the patient is intubated and hemodynamically unstable with uncertain GI absorption; UFH infusion with aPTT monitoring provides the required pharmacological control and reversibility in this critical phase.

ANSWER: D

Rationale:

Option D is correct. The severity stratification of PE divides patients into high-risk (massive) and intermediate-risk (submassive) categories. Massive PE is defined by hemodynamic instability: systolic BP below 90 mmHg for at least 15 minutes, vasopressor requirement, cardiac arrest, or signs of severe right heart failure with shock. This patient is hemodynamically stable (BP 122/78 mmHg, HR 90 bpm) — he does not meet the hemodynamic criteria for massive PE regardless of imaging findings. The combination of RV dysfunction on imaging (RV:LV ratio 1.1, above 0.9) and myocardial injury (elevated troponin) classifies this as intermediate-high-risk (submassive) PE — the highest-risk category within the hemodynamically stable group. The PEITHO trial assessed this exact population and found that tenecteplase reduced hemodynamic decompensation but significantly increased major bleeding without a 30-day mortality benefit, supporting anticoagulation alone as the primary treatment. Systemic thrombolysis is reserved for rescue (hemodynamic deterioration despite anticoagulation). Close inpatient monitoring is warranted given intermediate-high-risk classification.

• Option A: Option A is incorrect: troponin elevation alone does not constitute massive PE; massive PE requires hemodynamic instability by definition; this patient is hemodynamically stable.
• Option B: Option B is incorrect: intermediate-high-risk PE with RV dysfunction and troponin elevation should not be managed as low-risk; early discharge is not appropriate, and the risk stratification impacts monitoring intensity and treatment decisions.
• Option C: Option C is incorrect: RV:LV ratio above 1.0 is an imaging criterion for RV dysfunction (a component of intermediate-risk classification) — it does not in itself define massive PE or mandate systemic thrombolysis; hemodynamic instability is required for the massive PE definition.

ANSWER: B

Rationale:

Option B is correct. CDT (catheter-directed thrombolysis) provides a pharmacological advantage specifically in patients with relative contraindications to full-dose systemic thrombolysis. By advancing a multi-sidehole catheter directly into the pulmonary thrombus and infusing low-dose alteplase locally (approximately 0.5 to 1 mg/hr per catheter, total dose 8 to 24 mg), CDT reduces the systemic alteplase exposure by approximately 90% compared with the standard 100 mg systemic regimen. This dramatically reduces systemic plasminemia and major bleeding risk — directly relevant for this patient whose laparoscopic cholecystectomy 12 days ago represents a surgical site at risk of hemorrhage during systemic fibrinolysis. The ULTIMA trial demonstrated that CDT achieved superior RV/LV ratio improvement versus anticoagulation alone at 24 hours. While setup time (45 minutes) is a real consideration, the patient is hemodynamically unstable but not in cardiac arrest — 45 minutes of continued vasopressor support while preparing CDT is clinically defensible when the alternative (systemic alteplase) carries substantially higher bleeding risk.

• Option A: Option A is incorrect: CDT for PE is a performed clinical procedure supported by evidence (ULTIMA trial, SEATTLE II) and is used at PE response team centers; it is not limited to DVT treatment; while individual CDT devices may have specific FDA clearances, catheter-directed fibrinolysis for PE is a recognized and guideline-referenced treatment option.
• Option C: Option C is incorrect: CDT has not been demonstrated to achieve higher rates of complete clot dissolution than systemic thrombolysis in head-to-head trials; the advantage of CDT is reduced systemic bleeding exposure, not superior efficacy; systemic thrombolysis likely achieves faster initial pulmonary blood flow restoration.
• Option D: Option D is incorrect: while timing is critical, this patient is not in cardiac arrest — he has hemodynamic instability that is being supported with vasopressors; the 45-minute setup time for CDT is a clinically acceptable trade-off against significantly reduced major bleeding risk compared with systemic alteplase in a patient with recent abdominal surgery.

ANSWER: D

Rationale:

Option D is correct. Idarucizumab is the specific approved reversal agent for dabigatran. The dose is fixed at 5 g IV — not renally adjusted — administered as two consecutive 2.5 g boluses no more than 15 minutes apart. Renal impairment does not contraindicate idarucizumab; it is actually more important in CKD patients because dabigatran accumulates with reduced renal clearance, and complete initial reversal is essential. Idarucizumab binds dabigatran with approximately 350-fold higher affinity than dabigatran has for thrombin, forming an irreversible 1:1 neutralizing complex that is then excreted in urine. In the RE-VERSE AD trial, idarucizumab achieved median maximum reversal of 100% in patients with serious bleeding or urgent procedures.

• Option A: Option A is incorrect: andexanet alfa is specific for factor Xa inhibitors and has no mechanism or affinity for dabigatran; thrombin and factor Xa do not share sufficient structural homology at the active site to allow andexanet's decoy mechanism to capture dabigatran.
• Option B: Option B is incorrect: idarucizumab is not contraindicated in CKD and does not accumulate to cause paradoxical effects; 4F-PCC is a non-specific backup option when idarucizumab is unavailable, not the preferred first-line agent in CKD; the described mechanism of free dabigatran release from saturated idarucizumab binding sites is fabricated.
• Option C: Option C is incorrect: dabigatran is a direct thrombin inhibitor — a small synthetic molecule that directly occupies thrombin's active site; it does not work through antithrombin potentiation; protamine neutralizes heparin and LMWH through ionic charge interactions but has no mechanism of action against dabigatran.

ANSWER: B

Rationale:

Option B is correct. Rebound dabigatran anticoagulation after idarucizumab is a recognized pharmacokinetic phenomenon, particularly pronounced in patients with renal impairment. When idarucizumab is administered, it captures circulating free dabigatran but cannot access dabigatran sequestered in tissue compartments or loosely protein-bound fractions simultaneously. As idarucizumab (half-life approximately 45 minutes) is renally excreted along with the dabigatran-idarucizumab complex, dabigatran remaining in tissue depots redistributes back into the plasma compartment — re-establishing anticoagulant activity. In this patient with CKD (CrCl 38 mL/min), dabigatran's renal clearance is reduced (dabigatran is approximately 80% renally eliminated), meaning total body drug burden was elevated at the time of reversal — amplifying the redistribution pool. The RE-VERSE AD trial documented this phenomenon in a subset of patients. Management depends on clinical context: observation alone if no active hemorrhage; a second 5 g idarucizumab dose if clinically significant bleeding recurs or further surgery is needed.

• Option A: Option A is incorrect: post-operative medication-seeking is not a pharmacological explanation for dilute thrombin time re-elevation; the rebound is a well-documented pharmacokinetic phenomenon; attributing it to covert re-ingestion without clinical basis is inappropriate.
• Option C: Option C is incorrect: idarucizumab has no partial agonist mechanism and does not release dabigatran through tubuloglomerular feedback; the dissociation of the idarucizumab-dabigatran complex is negligible under physiological conditions — the rebound represents tissue redistribution of unbound dabigatran, not complex dissociation; the suggestion to permanently discontinue dabigatran based on rebound is not guideline-supported management.
• Option D: Option D is incorrect: the 5 g dose of idarucizumab is not weight or renal-adjusted — it is the correct dose regardless of CrCl; the rebound is not a dosing failure; a maintenance idarucizumab infusion protocol does not exist in any guideline or prescribing information.

ANSWER: C

Rationale:

Option C is correct. Dabigatran's dialyzability is a direct consequence of its relatively low protein binding (approximately 35%), which means a substantial fraction circulates as free drug in plasma water available for dialytic removal across the dialysis membrane. This contrasts sharply with factor Xa inhibitors (apixaban approximately 87% protein-bound, rivaroxaban approximately 92 to 95% protein-bound), which are not effectively removed by hemodialysis. The prescribing information for dabigatran explicitly notes dialyzability as a management option for severe overdose or accumulation. In this clinical scenario — rebound anticoagulation with new bleeding in a patient already on hemodialysis — dialysis serves as an adjunct to pharmacological reversal: it reduces the total dabigatran pool available for continued plasma redistribution, potentially attenuating further rebound. High-flux hemodialysis membranes provide more efficient removal than low-flux membranes due to greater membrane permeability. Hemodialysis does require anticoagulation of the extracorporeal circuit, which can be managed with regional citrate anticoagulation or minimal systemic heparin in a post-neurosurgical patient.

• Option A: Option A is incorrect: dabigatran is approximately 35% protein-bound — not 99%; it is dialyzable precisely because of its low protein binding; while circuit anticoagulation is a consideration, regional citrate protocols are available for patients at hemorrhagic risk.
• Option B: Option B is incorrect: dabigatran is present in plasma as well as tissue compartments; serum concentrations are measurable and clinically relevant — dilute thrombin time re-elevation reflects active plasma dabigatran concentration; dialysis of plasma water does reduce circulating drug.
• Option D: Option D is incorrect: dabigatran removal by hemodialysis occurs primarily via diffusive and convective transport across the dialysis membrane, not adsorption; high-flux membranes with larger pore sizes do achieve greater small-molecule removal than low-flux membranes; stating that all modalities achieve equivalent clearance regardless of membrane permeability is factually wrong.

ANSWER: A

Rationale:

Option A is correct. Anticoagulation restart after anticoagulant-associated ICH is one of the most challenging decisions in antithrombotic management, requiring individualized risk-benefit analysis. The key considerations are: annual ischemic stroke risk (CHA2DS2-VASc score), annual ICH recurrence risk (influenced by ICH location, presence of cerebral amyloid angiopathy, hypertension control, and anticoagulant type), time required for hematoma stabilization, and surgical healing. Most current guidelines (AHA/ASA Stroke, ESC Atrial Fibrillation, CHEST) recommend deferring anticoagulation for approximately 4 to 8 weeks after anticoagulant-associated ICH, with the decision made jointly by neurosurgery, neurology, and cardiology after repeat neuroimaging. In some patients, left atrial appendage occlusion devices represent an alternative to indefinite anticoagulation. The specific location of ICH also matters — lobar ICH (associated with cerebral amyloid angiopathy) carries higher recurrence risk than deep ICH.

• Option B: Option B is incorrect: permanent contraindication to anticoagulation is not the guideline recommendation after anticoagulant-associated ICH; many patients — particularly those with high-risk AF and deep ICH — benefit from carefully timed anticoagulation restart, and the risk-benefit calculation must be individualized.
• Option C: Option C is incorrect: resuming dabigatran at day 14 is too early in a patient who underwent craniotomy for a large ICH with midline shift; a fixed day-14 rule does not account for hematoma evolution, surgical wound healing, or neurological recovery; AF thromboembolic risk does not automatically exceed ICH recurrence risk in all patients.
• Option D: Option D is incorrect: surgical site healing at day 5 to 7 does not address ICH recurrence risk from the underlying cerebrovascular pathology; the CT findings are highly relevant — residual hematoma, perilesional edema, and blood-brain barrier disruption all affect the safety of anticoagulation restart; the claim that surgical evacuation addresses cerebrovascular fragility is incorrect.

ANSWER: B

Rationale:

Option B is correct. The weight- and INR-tiered dosing for 4F-PCC (Kcentra) uses 50 units/kg (maximum 5,000 units) for INR above 6 — this patient's INR of 9.4 requires the maximum dose tier. IV vitamin K 10 mg must be given simultaneously (not after a delay) for a critical pharmacokinetic reason: 4F-PCC provides immediate factor replacement, but the infused factors are cleared over the following hours according to their individual half-lives (factor VII is cleared first, approximately 4 to 6 hours; factor II last, approximately 60 to 72 hours). Warfarin continues to suppress endogenous vitamin K-dependent factor synthesis throughout this period. Without concurrent vitamin K to restore the hepatic synthesis of new factor proteins, the INR will rebound as PCC factors clear — creating a second window of over-anticoagulation. IV vitamin K 10 mg achieves measurable INR reduction within 6 to 8 hours through stimulation of new factor synthesis, providing the sustained reversal that bridges the gap as PCC factors are cleared.

• Option A: Option A is incorrect: 35 units/kg is the dosing tier for INR 4 to 6, not INR above 6; for INR 9.4 the 50 units/kg tier is required; additionally, delaying vitamin K administration is incorrect — simultaneous co-administration is the standard protocol.
• Option C: Option C is incorrect: 4F-PCC factor levels do not persist for 72 hours — factor VII is cleared within 4 to 6 hours, creating INR rebound without vitamin K; the claim that PCC provides 72 hours of hemostatic coverage is pharmacokinetically wrong.
• Option D: Option D is incorrect: 4F-PCC is not contraindicated in patients with bioprosthetic valves; bioprosthetic valves carry a lower thrombotic risk than mechanical valves and are not a contraindication to urgent procoagulant reversal for life-threatening hemorrhage; FFP would require 4 to 6 units (approximately 1,000 to 1,500 mL) with volume overload risk and slower onset than 4F-PCC.

ANSWER: A

Rationale:

Option A is correct. The majority of adverse reactions to IV vitamin K — including flushing, hypotension, dyspnea, urticaria, and anaphylaxis — are attributed not to phytonadione itself but to polyethoxylated castor oil (Cremophor EL, also called polyoxyethylated castor oil or PEG-35 castor oil), the solubilizing vehicle used in IV vitamin K formulations. Cremophor EL is also implicated in hypersensitivity reactions to other IV medications (cyclosporine, paclitaxel). Because oral vitamin K preparations (capsules, tablets, or drops) use different formulation vehicles without Cremophor EL, they do not carry the same hypersensitivity risk. Therefore, oral vitamin K 5 to 10 mg is a safe and appropriate substitute for this patient. The limitation is onset: oral vitamin K achieves meaningful INR reduction within 24 to 48 hours, versus 6 to 8 hours for IV vitamin K — acceptable in this case because 4F-PCC provides the immediate factor replacement and the oral vitamin K sustains it over time.

• Option B: Option B is incorrect: phytonadione does not act as a hapten and does not undergo metabolism that destroys a hapten-forming structure; this mechanism is fabricated; the reaction is attributed to the vehicle, not the vitamin K molecule itself.
• Option C: Option C is incorrect: direct mast cell activation by phytonadione itself regardless of formulation is not the established mechanism; oral vitamin K does not carry equivalent anaphylaxis risk to IV vitamin K; the vehicle (Cremophor EL) is the distinguishing factor between the two routes.
• Option D: Option D is incorrect: complement activation by polymerized vitamin K micelles is not the established mechanism for IV vitamin K reactions; Cremophor EL (not vitamin K micelles) is the implicated agent; while the route does matter, it is specifically the vehicle formulation that is causal, not micelle formation per se.

ANSWER: D

Rationale:

Option D is correct. The pharmacological case for 4F-PCC over FFP in this patient is primarily volume-based. 4F-PCC contains concentrated factors II, VII, IX, and X (plus proteins C and S) in a lyophilized form reconstituted in approximately 100 to 250 mL total volume. FFP, by contrast, contains clotting factors at normal plasma concentrations (approximately 1 unit activity/mL) — achieving equivalent factor replacement requires 4 to 6 units (approximately 200 to 250 mL each, totaling approximately 1,000 to 1,500 mL). In a volume-overloaded patient with diastolic heart failure and preserved ejection fraction, the diastolic non-compliance means the left ventricle cannot accommodate a sudden increase in preload; 1,000 to 1,500 mL of colloid infused over 1 to 2 hours would predictably precipitate acute pulmonary edema. The 100 to 250 mL volume of 4F-PCC avoids this entirely. Additionally, 4F-PCC achieves INR correction within 15 to 30 minutes, faster than FFP which requires thawing time (approximately 30 minutes) before administration.

• Option A: Option A is incorrect: albumin-containing products (albumin infusions, FFP) do not reliably shift fluid from the interstitium in patients with decompensated heart failure, and albumin content is not a rationale for FFP over PCC in VKA reversal; FFP's volume load would worsen rather than improve pulmonary edema in this patient.
• Option B: Option B is incorrect: the choice between 4F-PCC and FFP is not purely logistical — the volume difference is clinically significant in volume-sensitive patients; while FFP does require ABO compatibility testing, this is not the primary pharmacological rationale in this case.
• Option C: Option C is incorrect: warfarin over-anticoagulation does not cause a fibrinolytic state — warfarin depletes vitamin K-dependent coagulation factors but does not activate plasminogen or deplete alpha-2-antiplasmin; describing warfarin as causing fibrinolysis is pharmacologically wrong; 4F-PCC is designed specifically for VKA reversal and is not inferior to FFP in this respect.

ANSWER: C

Rationale:

Option C is correct. After major hemorrhage, warfarin restart requires balancing thrombotic risk (stroke from AF or thromboembolic risk from the valve indication) against the risk of re-bleeding. For bioprosthetic valves — which carry lower thrombotic risk than mechanical valves — warfarin is often continued for the first 3 months post-implantation and may be discontinued or continued based on additional risk factors. In the setting of major bleeding, most guidelines and expert consensus support a 1 to 2 week deferral once hemostasis is secured, followed by careful restart at a reduced dose with close INR monitoring. This patient's pre-event INR of 9.4 suggests her warfarin dose was excessive (likely amplified by a drug interaction or dietary change) — the restart dose should be meaningfully lower than the dose that produced this INR, with INR checks every 2 to 3 days initially to guide dose adjustment.

• Option A: Option A is incorrect: permanent discontinuation of anticoagulation is not the standard recommendation after a single major hemorrhage in a patient with a bioprosthetic valve; the hemorrhage was over-anticoagulation-related (INR 9.4), not spontaneous at therapeutic INR; transition to LAA occlusion is not indicated solely based on this event.
• Option B: Option B is incorrect: restarting at the same dose that produced INR 9.4 would reproduce the over-anticoagulation; dose reduction and close monitoring are mandatory after any significant INR excursion causing major bleeding.
• Option D: Option D is incorrect: bridging anticoagulation with therapeutic UFH for 5 days during warfarin loading is recommended for mechanical heart valves in select circumstances, not for bioprosthetic valves in the post-hemorrhage period; therapeutic UFH bridging in a patient 48 hours after pulmonary hemorrhage control carries substantial re-bleeding risk without established benefit for bioprosthetic valve thrombosis prevention.

ANSWER: C

Rationale:

Option C is correct. The fibrinogen level of 82 mg/dL is critically low — normal fibrinogen is 200 to 400 mg/dL and hemostatic sufficiency generally requires above 150 mg/dL. In the context of alteplase administration 3 to 4 hours earlier, this fibrinogen depletion reflects the systemic lytic state: plasmin generated by alteplase has consumed circulating fibrinogen (and factor V and VIII). The INR (1.3) and aPTT (38 seconds) can appear relatively normal despite fibrinogen depletion because these tests assess thrombin-dependent clotting factor function — they do not adequately reflect fibrinogen concentration. A low fibrinogen means that even if thrombin is generated normally, there is insufficient substrate for fibrin polymerization and clot formation, so endoscopic hemostasis will fail without fibrinogen replacement. Cryoprecipitate 10 units IV raises fibrinogen by approximately 50 to 70 mg/dL; the dose should be repeated until fibrinogen exceeds 150 mg/dL. TXA concurrently inhibits further plasmin-driven fibrinogen degradation.

• Option A: Option A is incorrect: fibrinogen of 82 mg/dL is critically low, not normal; fibrinogen below 100 mg/dL in the post-thrombolytic period mandates urgent replacement; delaying intervention risks hemorrhagic shock from an uncontrolled peptic ulcer bleed in a coagulopathic patient.
• Option B: Option B is incorrect: INR 1.3 does not indicate warfarin over-anticoagulation — this patient is not on warfarin; an INR of 1.3 represents mild prolongation consistent with mild factor depletion from plasmin activity, not VKA toxicity; 4F-PCC is not indicated here.
• Option D: Option D is incorrect: fibrinogen of 82 mg/dL in a post-thrombolytic patient does not represent chronic protein malnutrition; the acute drop after alteplase is pharmacologically explained by plasmin-mediated fibrinogenolysis; ignoring this and proceeding to endoscopy without fibrinogen replacement would result in inadequate hemostasis.

ANSWER: D

Rationale:

Option D is correct. Cryoprecipitate dosing for fibrinogen replacement in post-thrombolytic bleeding uses a standard empirical initial dose of 10 units IV. Each unit of cryoprecipitate contains approximately 150 to 250 mg of fibrinogen; in an average adult, each unit raises circulating fibrinogen by approximately 5 to 7 mg/dL (the increment depends on plasma volume, which varies with body weight and clinical state). Ten units therefore raises fibrinogen by approximately 50 to 70 mg/dL. For this patient starting at 82 mg/dL, 10 units should raise fibrinogen to approximately 132 to 152 mg/dL — near but possibly still below the 150 mg/dL target. The fibrinogen level must be rechecked after infusion, and additional doses should be given if the target is not met. There is no absolute maximum dose — the clinical priority is achieving fibrinogen above 150 mg/dL to support hemostasis. Simultaneously, tranexamic acid should be administered to slow ongoing plasmin-mediated fibrinogen degradation.

• Option A: Option A is incorrect: cryoprecipitate dosing is not weight-based in clinical practice — the standard initial dose is 10 units for adults regardless of weight; PT/INR normalization is not the monitoring target for cryoprecipitate — fibrinogen level is the direct endpoint.
• Option B: Option B is incorrect: a fixed single dose of 4 units is too low for fibrinogen replacement in a critically depleted patient; repeat dosing is not limited by a daily maximum or half-life restriction — fibrinogen replacement is guided by measured levels, and the urgency of active hemorrhage requires meeting the hemostatic target, not adhering to a fixed single dose.
• Option C: Option C is incorrect: the fibrinogen increment per unit of cryoprecipitate is approximately 5 to 7 mg/dL per unit, not a fixed 100 mg/dL per 10 units; individual variation in plasma volume means the increment varies; the concept of a hypercoagulable state from fibrinogen replacement in an actively bleeding patient is clinically incorrect.

ANSWER: A

Rationale:

Option A is correct. TXA (tranexamic acid) is a synthetic analogue of the amino acid lysine. Plasminogen contains multiple kringle domains — structural loop domains with lysine-binding sites that are essential for plasminogen's attachment to lysine residues exposed on fibrin within a clot. By competitively occupying these lysine-binding sites, TXA blocks plasminogen from binding to fibrin, preventing fibrin-bound plasminogen activation by tPA. Without fibrin-bound plasminogen, tPA cannot efficiently generate plasmin at the clot or fibrinogen surface — because tPA requires the ternary complex of fibrin, plasminogen, and tPA for maximum catalytic efficiency. The result is inhibition of ongoing fibrinogenolysis. TXA is therefore pharmacologically complementary to cryoprecipitate: cryoprecipitate replaces the fibrinogen already consumed by plasmin (substrate replacement), while TXA prevents further plasmin-driven fibrinogen consumption (mechanism inhibition). Together they address both the deficit and the ongoing driver of the deficit.

• Option B: Option B is incorrect: TXA does not inhibit alteplase directly; it does not bind to tPA's fibronectin finger domain or any other alteplase structural domain; TXA acts on plasminogen, not on the plasminogen activator.
• Option C: Option C is incorrect: TXA does not activate TAFI; its mechanism is direct competitive blockade of plasminogen lysine-binding sites; TAFI activation by TXA is not a recognized pharmacological mechanism.
• Option D: Option D is incorrect: TXA does not specifically inhibit cathepsin B; while TXA may have some broad inhibitory effects on certain cysteine proteases at high concentrations, this is not its clinically relevant mechanism; its antifibrinolytic action is through plasminogen lysine-binding domain blockade, not cathepsin B inhibition.

ANSWER: B

Rationale:

Option B is correct. The decision to restart anticoagulation after major GI hemorrhage in a patient with a life-threatening indication (massive PE) requires individualized risk-benefit assessment. Venous thromboembolism — particularly massive PE — carries substantial early recurrence risk without anticoagulation; PE recurrence without anticoagulation carries significant mortality. For patients in whom hemostasis has been achieved, early restart of anticoagulation (within 24 to 72 hours) is generally supported by guidelines when the bleeding risk is judged acceptable after endoscopic hemostasis. If anticoagulation cannot be safely restarted within 48 hours (e.g., ongoing hemorrhagic risk), a retrievable IVC filter can be placed as a temporary mechanical barrier against pulmonary embolism while the decision is deferred. The filter is typically removed once anticoagulation is resumed. This patient has a high-risk PE indication (massive PE requiring thrombolysis), which strengthens the argument for early anticoagulation restart once hemostasis is secured.

• Option A: Option A is incorrect: permanent anticoagulation contraindication after a single episode of peptic ulcer GI bleeding is not guideline-supported; with adequate endoscopic hemostasis, proton pump inhibitor therapy, and Helicobacter pylori treatment if applicable, the re-bleeding risk is substantially reduced; IVC filters are not a permanent substitute for anticoagulation and carry their own long-term thrombotic complications.
• Option C: Option C is incorrect: a fixed 7-day waiting period is not evidence-based; the timing of anticoagulation restart after GI bleeding depends on clinical hemostasis, not on a fixed mucosal healing interval; the concept that fibrin plug disruption invariably causes re-bleeding at less than 7 days overstates the risk.
• Option D: Option D is incorrect: a 30-day anticoagulation hold has no pharmacological basis — fibrinogen and plasminogen reserves normalize within hours to days after thrombolytic therapy, not 30 days; holding anticoagulation for 30 days in a massive PE patient would carry catastrophic VTE recurrence risk.

ANSWER: A

Rationale:

Option A is correct. The definitive treatment of DIC is removal of the underlying trigger — in this case, aggressive treatment of the Streptococcus pneumoniae sepsis with appropriate antibiotics and vasopressor/hemodynamic support. No hemostatic therapy can permanently correct DIC while systemic thrombin generation driven by the infectious trigger continues. Concurrent hemostatic replacement addresses the immediate coagulopathy: FFP replaces all consumed coagulation factors broadly; cryoprecipitate provides concentrated fibrinogen replacement targeting above 150 mg/dL (this patient's fibrinogen of 58 mg/dL requires urgent replacement); platelet transfusion for counts below 50,000/mcL with active bleeding. TXA is specifically contraindicated in sepsis-associated DIC: fibrinolysis in this setting is reactive secondary fibrinolysis protecting against microvascular occlusion — inhibiting it with TXA would extend organ ischemia by allowing microvascular thrombi to persist.

• Option B: Option B is incorrect: TXA is not indicated as first-line therapy for sepsis-associated DIC; the primary fibrinolysis rationale applies specifically to APL-associated DIC — generalizing it to all DIC is a pharmacological category error; TXA in sepsis DIC risks worsening the microvascular thrombosis causing the purpura fulminans.
• Option C: Option C is incorrect: 4F-PCC contains factors II, VII, IX, and X but does not contain fibrinogen in meaningful amounts; this patient's most critically depleted hemostatic component is fibrinogen (58 mg/dL) which requires cryoprecipitate, not PCC; 4F-PCC is the agent for VKA reversal, not DIC factor replacement.
• Option D: Option D is incorrect: therapeutic heparin infusion is not the mandatory first-line intervention for all DIC presentations; heparin is considered only in DIC with predominant thrombotic manifestations (purpura fulminans, acral ischemia) when bleeding is not the primary concern — this patient is actively bleeding from multiple sites, making therapeutic heparin dangerous without careful assessment; beginning heparin as the first step before factor replacement in a bleeding patient risks catastrophic hemorrhage.

ANSWER: C

Rationale:

Option C is correct. Current DIC management guidelines (British Committee for Standards in Haematology, International Society on Thrombosis and Haemostasis) recognize a specific indication for heparin in DIC: patients in whom the clinical picture is dominated by thrombotic manifestations — purpura fulminans, acral ischemia, large vessel thrombosis — rather than hemorrhage. In this patient, progressive digital necrosis advancing proximally despite replacement therapy indicates that ongoing microvascular fibrin deposition is the primary threat; the bleeding has decreased (fibrinogen 142 mg/dL, bleeding from IV sites diminished). Under these conditions, low-dose therapeutic heparin targeting anti-Xa 0.3 to 0.5 IU/mL is considered to interrupt the cycle of systemic thrombin generation driving microvascular occlusion — recognizing that the harm from limb loss equals or exceeds the hemorrhagic risk when factor levels are being maintained. This must always be accompanied by concurrent blood product replacement (FFP, cryoprecipitate) to prevent catastrophic bleeding. The decision is individualized and represents a carefully weighed risk-benefit judgment.

• Option A: Option A is incorrect: coexisting thrombotic manifestations and active bleeding is not an absolute contraindication to heparin consideration in DIC — guidelines explicitly recognize this difficult clinical scenario and provide qualified guidance supporting heparin for thrombosis-dominant DIC with concurrent factor replacement; characterizing this as never appropriate overstates the contraindication.
• Option B: Option B is incorrect: full therapeutic heparin (80 units/kg bolus + 18 units/kg/hr) is not the standard recommendation for thrombosis-dominant DIC; low-dose therapeutic heparin targeting anti-Xa 0.3 to 0.5 IU/mL is more appropriate; full-dose bolus anticoagulation in a coagulopathic patient risks catastrophic hemorrhage.
• Option D: Option D is incorrect: this patient's thrombocytopenia and thrombosis are explained by DIC from sepsis — not by HITT; HITT requires prior heparin exposure and a specific clinical-pathological presentation with a positive platelet factor 4 antibody assay; there is no indication from the case that this patient received heparin prior to this admission; attributing DIC findings to HITT without supporting evidence is clinically inappropriate.

ANSWER: B

Rationale:

Option B is correct. In sepsis-associated DIC, the pathophysiology involves systemic thrombin generation from tissue factor release by activated endothelium and monocytes, leading to widespread microvascular fibrin deposition. Simultaneously, tPA (tissue plasminogen activator) released from endothelium activates plasminogen to plasmin in a reactive secondary response — this secondary fibrinolysis serves to limit the extent of microvascular fibrin accumulation and preserve capillary patency. This protective fibrinolysis is what drives the elevated D-dimer and reduced fibrinogen observed in DIC. Administering TXA would block plasminogen's binding to fibrin (via kringle domain inhibition), shutting down this protective secondary fibrinolysis. The consequence would be persistence and accumulation of microvascular fibrin thrombi — worsening the purpura fulminans, extending digit and foot ischemia, and increasing multi-organ failure from microvascular ischemia in kidneys, lungs, and liver. TXA is beneficial only in primary hyperfibrinolytic states (APL-associated DIC, where leukemic promyelocyte-driven plasminogen activator release is the initiating event, not a reactive response) or in isolated fibrinolytic states (post-thrombolytic bleeding, trauma hemorrhage).

• Option A: Option A is incorrect: TXA does not activate protein C and has no mechanism involving protein C activation; its mechanism is purely plasminogen-focused, blocking kringle domain lysine-binding sites; protein C is not in TXA's mechanism of action pathway.
• Option C: Option C is incorrect: TXA does not inhibit antithrombin III; TXA has no known interaction with antithrombin and does not affect thrombin directly; its mechanism is entirely on the fibrinolytic pathway at the level of plasminogen activation.
• Option D: Option D is incorrect: TXA's contraindication in sepsis DIC is based on the pathophysiological mechanism (protective reactive fibrinolysis), not on the platelet count; there is no platelet count threshold that makes TXA safe in sepsis-associated DIC; the contraindication is categorical for this DIC phenotype.

ANSWER: D

Rationale:

Option D is correct. The distinction between APL-associated DIC and sepsis-associated DIC is mechanistic, not superficial. In sepsis-induced DIC, the initiating event is systemic thrombin generation from tissue factor activation; fibrinolysis is secondary and reactive. In APL, the initiating event is primary hyperfibrinolysis: leukemic promyelocytes express high levels of annexin II (a cell surface co-receptor for tPA and plasminogen that dramatically amplifies plasminogen activation) and membrane-bound urokinase plasminogen activator (uPA), generating plasmin as the primary coagulopathic driver before any significant thrombin activation. This primary fibrinolytic state consumes fibrinogen, factor V, and factor VIII — producing severe hemorrhage. Because fibrinolysis is primary rather than reactive in APL, inhibiting it with TXA reduces pathological bleeding without the risk of extending microvascular thrombosis that makes TXA dangerous in sepsis DIC. ATRA (all-trans retinoic acid) induces promyelocyte differentiation, progressively eliminating annexin II and uPA expression — TXA bridges the patient until ATRA takes effect (typically days to weeks). Once ATRA achieves remission induction, the hyperfibrinolytic driver is removed and TXA can be discontinued.

• Option A: Option A is incorrect: the TXA indication in APL is not based on thrombocytopenia or platelet count; it is mechanistically driven by the primary hyperfibrinolytic pathophysiology of APL; applying a "platelet-count-dependent pharmacological logic" to all DIC subtypes is factually wrong.
• Option B: Option B is incorrect: ATRA does not directly activate fibrinolysis as a side effect; the fibrinolysis in APL is driven by the malignant promyelocytes themselves (annexin II, uPA), not by ATRA therapy; TXA addresses the DIC mechanism, not an ATRA side effect.
• Option C: Option C is incorrect: APL typically presents with bleeding-predominant DIC (severe hemorrhage from primary fibrinolysis), not thrombosis-dominant DIC; TXA is not given to counter heparin's anticoagulant effect; this option contains multiple pharmacological errors.