Rifampicin accelerates the CYP450-mediated metabolism of:

Correct Answer: B

Rationale: Rifampicin accelerates the CYP450-mediated metabolism of warfarin (B), a vitamin K antagonist anticoagulant, reducing its efficacy and requiring dose adjustments to maintain therapeutic INR levels. It also affects corticosteroids (A), like prednisolone, lowering their anti-inflammatory effects. Streptomycin (C), an aminoglycoside, isn't metabolized by CYP450, relying on renal clearance. Digoxin (D) metabolism isn't significantly altered by rifampicin, though P-glycoprotein induction may reduce levels. Oestrogen (original E) metabolism is accelerated, reducing contraceptive efficacy. Rifampicin's potent CYP450 induction, particularly CYP3A4, stems from its activation of the pregnane X receptor, impacting pharmacokinetics of co-administered drugs, critical in TB management where polypharmacy is common.

Correct Answer: B

Rationale: AZT + lamivudine + lopinavir/ritonavir (B) is an accepted first-line HIV therapy, combining two nucleoside reverse transcriptase inhibitors (NRTIs: AZT, lamivudine) with a boosted protease inhibitor (lopinavir/ritonavir), effectively suppressing viral replication and preventing resistance. AZT + ddC (A) lacks a third class, reducing efficacy. Ritonavir + amprenavir + enfuvirtide (C) mixes protease inhibitors and an entry inhibitor, not typical first-line. AZT + lamivudine + nevirapine (D), with an NNRTI, is viable but less common now versus integrase inhibitors. Modern guidelines favor integrase-based regimens (e.g., dolutegravir), but B reflects older, still-accepted triple therapy, balancing potency and resistance barriers.

Correct Answer: B

Rationale: Melphalan (B) is associated with profound and prolonged myelosuppression, an alkylating agent causing dose-limiting neutropenia and thrombocytopenia, common in multiple myeloma treatment. Chlorambucil (A) causes milder, reversible suppression. BCNU (C), or carmustine, also causes severe, delayed myelosuppression, notable in brain tumors. Bleomycin (D) primarily causes pulmonary toxicity, not myelosuppression. Vincristine (original E) affects nerves, not marrow. Melphalan's DNA cross-linking halts cell division, effective in hematologic malignancies, but its marrow toxicity requires growth factor support or dose delays, balancing efficacy with infection risk.

Correct Answer: C

Rationale: Recombinant human erythropoietin (EPO) treats anemia of chronic renal failure (C), stimulating red blood cell production in kidneys unable to produce endogenous EPO, improving quality of life in dialysis patients. It's not used for iron-deficient anemia (A); iron supplementation is needed. Sickle cell anemia (B) relies on hydroxyurea, not EPO. It treats AZT-related anemia (D) in HIV, countering marrow suppression. It's ineffective in clozapine-induced agranulocytosis (original E). EPO's targeted stimulation of erythropoiesis, monitored via hemoglobin levels, reduces transfusion needs, though hypertension and thrombosis risks require oversight.

Correct Answer: D

Rationale: Protonation (D) is the correct answer, as it describes the process where a weak acid gains a proton (H⁺) in a low pH environment, becoming un-ionized, less water-soluble, and more lipid-soluble. This enhances membrane permeation, as seen with aspirin in the stomach (pH ~2). Distribution (A) is movement into tissues, not a solubility change. Elimination (B) is excretion, unrelated to solubility shifts. First-pass effect (C) is hepatic metabolism post-absorption, not a physical process. Permeation (original E) is movement across membranes, not the solubility change itself. Protonation leverages the Henderson-Hasselbalch equation, where a weak acid's pKa (e.g., aspirin 3.5) relative to pH dictates ionization, impacting absorption and distribution in acidic compartments like the stomach.