Vasoactive Peptide Pharmacology

Correct Answer

B — Captopril, enalapril, and lisinopril

Rationale

Captopril, enalapril, and lisinopril are all angiotensin-converting enzyme inhibitors — drugs that block the zinc active site of angiotensin-converting enzyme and prevent conversion of angiotensin I to angiotensin II. Losartan, valsartan, and candesartan are angiotensin receptor blockers. Aliskiren is a direct renin inhibitor. Spironolactone and eplerenone are aldosterone antagonists.

Correct Answer

C — Direct renin inhibitor

Rationale

Aliskiren is the only clinically available direct renin inhibitor. It is the sole representative of this drug class in current clinical use. Angiotensin-converting enzyme inhibitors include captopril and enalapril. Angiotensin receptor blockers include losartan and valsartan. Aldosterone antagonists include spironolactone and eplerenone.

Correct Answer

A — Angiotensin-converting enzyme inhibitor

Rationale

Fosinopril is an angiotensin-converting enzyme inhibitor. It is distinguished within the class by its dual hepatic and renal elimination pathway, but its class membership is that of an angiotensin-converting enzyme inhibitor. Aliskiren is the direct renin inhibitor. Losartan and valsartan are angiotensin receptor blockers. Beta-adrenergic receptor antagonists such as metoprolol belong to an entirely separate drug class.

Correct Answer

D — Captopril

Rationale

Captopril and lisinopril are the two angiotensin-converting enzyme inhibitors that are pharmacologically active as administered. All other agents in the class — including enalapril, ramipril, and perindopril — are ester prodrugs that require hepatic hydrolysis to release their active diacid forms. Captopril is therefore classified in the active-drug subgroup of the angiotensin-converting enzyme inhibitor class, while enalapril, ramipril, and perindopril are classified as prodrugs.

Correct Answer

B — Enalapril

Rationale

Enalapril is an ester prodrug — it is administered as an inactive compound and converted by hepatic hydrolysis to its active form, enalaprilat. Ramipril and perindopril are also classified as ester prodrugs. Captopril and lisinopril are classified as active-as-administered agents requiring no conversion. Fosinopril is an ester prodrug as well, but is additionally distinguished by its dual hepatic and renal elimination pathway — a separate classification property tested elsewhere in this module.

Correct Answer

A — Aldosterone antagonist

Rationale

Spironolactone is classified as an aldosterone antagonist — a mineralocorticoid receptor antagonist that blocks aldosterone's effects at the renal collecting duct. Eplerenone is the other major aldosterone antagonist. Angiotensin-converting enzyme inhibitors include captopril and lisinopril. Angiotensin receptor blockers include losartan and valsartan. The only direct renin inhibitor in current clinical use is aliskiren.

Correct Answer

C — Accumulation of bradykinin in the pulmonary interstitium, sensitizing airway sensory fibers

Rationale

Angiotensin-converting enzyme has dual substrate specificity: it converts angiotensin I to angiotensin II and degrades bradykinin. When the enzyme is blocked, bradykinin accumulates in tissues including the pulmonary interstitium, where it sensitizes airway sensory fibers and lowers the cough threshold. The cough is dry and non-productive and does not respond to antihistamines. Angiotensin II levels fall with angiotensin-converting enzyme inhibition rather than rise. Prostaglandin synthesis and direct bronchial effects are not part of this mechanism.

Correct Answer

A — The reaction is mediated by bradykinin accumulation, not by histamine release

Rationale

Angiotensin-converting enzyme inhibitor-induced angioedema is bradykinin-mediated, not histamine-mediated. Because angiotensin-converting enzyme normally degrades bradykinin, blocking the enzyme allows bradykinin to accumulate and cause vascular permeability and swelling. Antihistamines block histamine receptors and are effective in IgE-mediated allergic reactions, but they have no effect on bradykinin-driven swelling. This distinction is clinically critical: epinephrine may provide temporary benefit through vasoconstriction, but the definitive treatment is immediate discontinuation of the angiotensin-converting enzyme inhibitor. Option B describes allergic angioedema, which is a different mechanism entirely.

Correct Answer

D — Fosinopril has approximately equal hepatic and renal elimination, so it accumulates far less when kidney function declines

Rationale

All angiotensin-converting enzyme inhibitors are eliminated primarily by the kidney, and most require dose reduction when glomerular filtration rate falls below 30 mL/min. Fosinopril is the exception: it has approximately equal hepatic and renal elimination, meaning that as renal function declines, hepatic clearance compensates and the drug does not accumulate to the same extent. This dual elimination pathway makes fosinopril the preferred angiotensin-converting enzyme inhibitor in patients with advanced chronic kidney disease. Fosinopril is not exclusively hepatic — it is a dual-pathway agent, which is the basis of its advantage. Fosinopril is also a prodrug requiring hepatic conversion, not an active-as-administered agent.

Correct Answer

B — Dilation of the efferent arteriole, reducing intraglomerular filtration pressure

Rationale

Angiotensin II normally constricts the efferent arteriole, maintaining intraglomerular pressure. In diabetic nephropathy this pressure is pathologically elevated, driving protein across the glomerular membrane. Angiotensin-converting enzyme inhibitors reduce angiotensin II, allowing the efferent arteriole to dilate and intraglomerular pressure to fall. This reduces the filtration force acting across the glomerular membrane, decreasing proteinuria and slowing structural damage. Angiotensin-converting enzyme inhibitors do not constrict the afferent arteriole, and they reduce aldosterone rather than increase it.

Correct Answer

A — Removal of angiotensin II-dependent efferent arteriolar constriction causes intraglomerular filtration pressure to collapse

Rationale

In bilateral renal artery stenosis, reduced arterial inflow forces the kidney to rely on angiotensin II-mediated constriction of the efferent arteriole to maintain glomerular filtration pressure. When angiotensin-converting enzyme inhibitors reduce angiotensin II, this compensatory efferent tone is lost and filtration pressure falls, precipitating acute kidney injury. This is not a bradykinin effect, not an afferent arteriolar effect, and not related to potassium. The same mechanism operates in a patient with a single functioning kidney and unilateral renal artery stenosis.

Correct Answer

C — Poor oral bioavailability and primary hepatobiliary elimination

Rationale

Aliskiren has poor oral bioavailability of approximately 2 to 3 percent, primarily due to limited gastrointestinal absorption. Despite this, once-daily dosing is effective because the drug binds renin with high affinity and has a prolonged duration of action. Aliskiren is eliminated primarily via the hepatobiliary route as unchanged drug, with minimal renal excretion. This contrasts with most angiotensin-converting enzyme inhibitors, which are renally eliminated. The hepatobiliary elimination pathway means aliskiren does not accumulate proportionally as renal function declines, though its pharmacodynamic risks in renal impairment are unchanged.

Correct Answer

D — Reduced aldosterone activity increases proximal tubular sodium reabsorption, and lithium is reabsorbed by the same mechanism

Rationale

Angiotensin-converting enzyme inhibitors suppress aldosterone secretion. With less aldosterone acting on the collecting duct, the kidney compensates by increasing sodium reabsorption at the proximal tubule. Lithium is handled similarly to sodium in the proximal tubule and is reabsorbed by the same transporters; when proximal sodium reabsorption increases, lithium reabsorption increases proportionally, raising plasma lithium levels and creating toxicity risk. This interaction requires monitoring serum lithium within one to two weeks of starting or changing an angiotensin-converting enzyme inhibitor in patients taking lithium.

Correct Answer

B — Suppression of the fetal renin-angiotensin-aldosterone system impairs renal tubular development, causing fetal anuria and oligohydramnios

Rationale

The developing fetal kidney depends on its own renin-angiotensin-aldosterone system for normal tubular development. When angiotensin-converting enzyme inhibitors cross the placenta and suppress fetal angiotensin II signaling, the result is fetal renal tubular dysgenesis — the kidney cannot develop its normal concentrating and excretory function. Fetal anuria leads to oligohydramnios (reduced amniotic fluid), which in turn causes limb contractures, pulmonary hypoplasia, and potentially neonatal death. This mechanism is shared by angiotensin receptor blockers. Pulmonary hypoplasia results from oligohydramnios impairing lung development, not from direct surfactant inhibition.

Correct Answer

C — Switch enalapril to an angiotensin receptor blocker, which blocks angiotensin II effects without affecting bradykinin metabolism

Rationale

The dry cough is caused by bradykinin accumulation: angiotensin-converting enzyme normally degrades bradykinin, and when the enzyme is blocked, bradykinin builds up in the pulmonary interstitium and sensitizes airway sensory fibers. Because the mechanism is bradykinin-driven, treatments that do not address bradykinin accumulation — including beta-agonist inhalers, antihistamines, and dose reduction — are ineffective. Angiotensin receptor blockers block the AT1 receptor downstream of angiotensin-converting enzyme, reducing angiotensin II effects without touching bradykinin metabolism; bradykinin continues to be degraded normally and the cough resolves in virtually all patients. Aliskiren blocks renin upstream but is not indicated as a replacement in heart failure with reduced ejection fraction and does not have the same evidence base as angiotensin receptor blockers for this substitution.

Correct Answer

A — Angiotensin-converting enzyme inhibitors

Rationale

Angiotensin-converting enzyme inhibitors are preferred in patients with diabetic nephropathy and proteinuria because they reduce intraglomerular hypertension through a specific mechanism: by lowering angiotensin II, they allow the efferent arteriole to dilate, which reduces the filtration pressure driving protein across the glomerular membrane. This mechanism slows progressive kidney damage independently of blood pressure lowering. The Lewis trial with captopril established this benefit in type 1 diabetes; subsequent trials confirmed the same effect in type 2 diabetes. Calcium channel blockers, thiazides, and beta blockers lower blood pressure but do not produce the same targeted reduction in intraglomerular pressure.

Correct Answer

D — The swelling is driven by bradykinin accumulation, which is not blocked by antihistamines or corticosteroids

Rationale

Angiotensin-converting enzyme inhibitor-induced angioedema is bradykinin-mediated, not histamine-mediated. Lisinopril blocks angiotensin-converting enzyme, which normally degrades bradykinin; bradykinin accumulates and increases vascular permeability, producing angioedema. Because histamine plays no role in this reaction, antihistamines such as diphenhydramine are ineffective. Corticosteroids also do not block bradykinin. The absence of urticaria and pruritus — features of histamine-mediated allergic reactions — supports this distinction. The immediate intervention is discontinuation of the angiotensin-converting enzyme inhibitor. Epinephrine may provide temporary relief in laryngeal involvement through vasoconstriction but does not address the underlying mechanism.

Correct Answer

B — Fosinopril

Rationale

Fosinopril is the preferred angiotensin-converting enzyme inhibitor in advanced chronic kidney disease because it has approximately equal hepatic and renal elimination pathways. When renal function declines, hepatic clearance compensates and the drug does not accumulate proportionally. All other angiotensin-converting enzyme inhibitors — including enalapril, ramipril, and lisinopril — are eliminated primarily by the kidney and require dose reduction or accumulate when glomerular filtration rate falls substantially. The pharmacodynamic risks of angiotensin-converting enzyme inhibitors in chronic kidney disease (hyperkalemia, acute kidney injury) apply regardless of the agent selected, but fosinopril's dual elimination minimizes the pharmacokinetic risk of drug accumulation.