The following drugs obey non-linear (dose-dependent) elimination pharmacokinetics:

Correct Answer: C

Rationale: Phenytoin (C) exhibits non-linear kinetics, with saturable hepatic metabolism (CYP2C9) causing half-life to increase at high doses (e.g., >300 mg/day). Aspirin overdose (A) and ethanol (D) are zero-order at high levels, also correct but C is chosen. Heparin (B) is complex, not purely non-linear. Ceftazidime (original E) is first-order. Non-linear kinetics, as with phenytoin, complicate dosing (e.g., toxicity risk), requiring monitoring, unlike linear drugs with predictable clearance.

Correct Answer: A

Rationale: Ciclosporin (A) is a CYP3A substrate, metabolized in the liver, affecting its immunosuppressive levels (e.g., transplant therapy). Clarithromycin (B) is too, also correct but A is chosen. Phenytoin (C) uses CYP2C9. Adrenaline (D) is COMT/MAO-metabolized. Warfarin (original E) is CYP2C9. CYP3A's broad substrate range, critical in drug interactions (e.g., with grapefruit juice), shapes ciclosporin's pharmacokinetics, necessitating monitoring.

Correct Answer: D

Rationale: Smaller digoxin doses are required in severe renal failure (D), as its renal clearance (GFR <10 mL/min) drops, prolonging half-life, risking toxicity. Option A is false (pH may rise). Option B is incorrect (phenytoin range adjusts minimally). Option C lacks evidence. Option E (original) about omeprazole is false. Digoxin's renal dependence, critical in heart failure, necessitates adjustment, a key pharmacokinetic shift in renal impairment.

Correct Answer: D

Rationale: Diffusion across membranes depends on pKa (ionization state), pH (proportion of non-ionized form via Henderson-Hasselbalch), and lipid solubility (membrane permeability). Molecular weight also influences diffusion but isn't listed. A, B, and C are individually correct, but D (‘All of the above') is the most complete answer, encompassing all key factors. This reflects how physicochemical properties dictate drug movement, critical for pharmacokinetics and drug design.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.