Miscellaneous Cytotoxics and Supportive Pharmacology
Hydroxyurea, asparaginase, immunomodulatory drugs, CYP450 interactions, neuropathy, and secondary malignancy
ABVD = doxorubicin, bleomycin, vinblastine, dacarbazine · ALL = acute lymphoblastic leukemia · AML = acute myeloid leukemia · CIPN = chemotherapy-induced peripheral neuropathy · CRBN = cereblon · CYP = cytochrome P450 · del(5q) = deletion 5q · HbF = fetal hemoglobin · HbS = hemoglobin S · HSCT = hematopoietic stem cell transplantation · IMiD = immunomodulatory drug · KMT2A = lysine methyltransferase 2A · MDS = myelodysplastic syndrome · MM = multiple myeloma · PEG = polyethylene glycol · REMS = Risk Evaluation and Mitigation Strategy · RNR = ribonucleotide reductase · SCD = sickle cell disease · t-MN = treatment-related myeloid neoplasm · VTE = venous thromboembolism
Hydroxyurea and Asparaginase: Distinct Mechanisms
- Scavenges tyrosyl radical of RNR → blocks dNTP synthesis → S-phase arrest
- Oncology: essential thrombocythemia, polycythemia vera, CML cytoreduction
- SCD: reactivates gamma-globin gene → HbF increases → less HbS polymerization
- SCD benefit: fewer vaso-occlusive crises, acute chest syndrome, stroke
- Toxicity: myelosuppression, macrocytosis (benign), leg ulcers
- Renal clearance: dose reduce if creatinine clearance below 60 mL/min
- Hydrolyzes circulating asparagine → starves ALL blasts lacking asparagine synthetase
- Normal cells protected: endogenous asparagine synthesis intact
- PEG-asparaginase: t½ ~5.5–7 days (vs 1.2 days native); less frequent dosing
- Hypersensitivity: 10–20%; silent inactivation by neutralizing antibodies
- Toxicities: pancreatitis, coagulopathy (fibrinogen ↓, antithrombin III ↓), hyperglycemia, hepatotoxicity
- Central venous sinus thrombosis: ~1–4%; anticoagulate promptly
Immunomodulatory Drugs: Cereblon-Mediated Mechanism
| Feature |
Thalidomide |
Lenalidomide |
Pomalidomide |
| Mechanism |
CRBN binding → Ikaros/Aiolos degradation |
Same + CK1α degradation (del[5q] MDS activity) |
Highest potency for Ikaros/Aiolos degradation |
| Key indication |
MM (relapsed) |
MM (frontline + maintenance); del(5q) MDS |
MM after lenalidomide + proteasome inhibitor failure |
| Dose-limiting toxicity |
Neuropathy, DVT |
Myelosuppression, VTE |
Myelosuppression, VTE |
| Metabolism |
Non-enzymatic hydrolysis |
Renal excretion (dose adjust for renal impairment) |
CYP1A2 + CYP3A4 (interactions with inducers) |
| REMS / teratogenicity |
All three: absolute contraindication in pregnancy; mandatory REMS enrollment, pregnancy testing, dual contraception |
CYP450 High-Risk Interactions and Secondary Malignancy
- Azoles inhibit CYP3A4 → vincristine exposure rises
- Risk: fatal vincristine neurotoxicity at standard doses
- Reduce vincristine to 50–75% or use less potent CYP3A4 inhibitor
- Paroxetine/fluoxetine inhibit CYP2D6
- Tamoxifen → endoxifen (active) conversion falls 65–75%
- Use venlafaxine, citalopram, or escitalopram instead
- Alkylating agents: latency 5–10 years; MDS first; del(5q)/del(7q); poor prognosis
- Topo II inhibitors (etoposide, anthracyclines): latency 1–3 years; de novo AML; KMT2A rearrangement
- KMT2A-rearranged t-MN: can respond to induction; allogeneic HSCT in first remission
CIPN Treatment: Duloxetine Is the Only Level I Evidence Agent
For established chemotherapy-induced peripheral neuropathy pain, duloxetine (start 30 mg daily, titrate to 60 mg daily) is the only agent with Level I randomized controlled trial evidence of benefit (ACCRU Alliance trial). Gabapentin, pregabalin, and amitriptyline have equivocal evidence. Calcium/magnesium infusions for oxaliplatin neuropathy prevention failed in randomized trials and are no longer recommended. Dose reduction or schedule modification remains the most effective neuropathy-sparing strategy when oncologically acceptable.