During cancer chemotherapy:

Correct Answer: A

Rationale: Infection is the commonest life-threatening complication during cancer chemotherapy (A), due to myelosuppression reducing neutrophils, increasing sepsis risk from opportunistic pathogens. It's often from the patient's gut flora (B), like E. coli, translocating during mucositis. Pyrexia is usually present (C is incorrect), a key sign of febrile neutropenia. Conception must be avoided (D), due to teratogenic risks. Second malignancies (original E) are a long-term risk, not immediate. Chemotherapy's immunosuppression, especially with alkylating agents or antimetabolites, disrupts immune barriers, necessitating prompt antibiotic therapy and G-CSF in high-risk cases.

Correct Answer: A

Rationale: Quantal dose-response curves are often used for determining the therapeutic index of a drug (A), the ratio of TD50 (toxic dose in 50% of subjects) to ED50 (effective dose in 50%), assessing safety (e.g., penicillin's high TI). Option B is incorrect; maximal efficacy is derived from graded curves, measuring continuous responses (e.g., blood pressure). Option C is false; inhibitors shift curves (e.g., rightward with competitive antagonists) but don't invalidate them. Option D is wrong; quantal curves apply to both intact subjects and tissues (e.g., lethality studies). Option E (original) about statistical variation fits graded curves better. Quantal curves, plotting all-or-none responses (e.g., survival), are key in toxicology and clinical trials for balancing efficacy and toxicity.

Correct Answer: A

Rationale: Acetylation (A) is a phase II drug-metabolizing reaction, conjugating drugs (e.g., isoniazid) with acetyl-CoA to increase water solubility and excretion, catalyzed by N-acetyltransferases. Deamination (B), hydrolysis (C), oxidation (D), and reduction (original E) are phase I reactions, modifying drug structure (e.g., CYP450 oxidation of diazepam) to expose functional groups. Phase II reactions, like acetylation, glucuronidation, or sulfation, typically follow, enhancing elimination. Acetylation's polymorphic nature (fast vs. slow acetylators) affects drug toxicity (e.g., isoniazid neuropathy), a key consideration in personalized medicine, distinguishing it from phase I's oxidative processes.

Correct Answer: A

Rationale: Heparin and protamine (A) is a good example of chemical antagonism, where protamine, a positively charged protein, binds and neutralizes negatively charged heparin, reversing its anticoagulant effect without receptor interaction. Protamine and zinc (B) form insulin complexes, not antagonism. Heparin and prothrombin (C) interact indirectly via clotting factors, not chemical binding. Option D is incorrect. This direct physicochemical interaction, distinct from receptor-based antagonism, is clinically vital in heparin overdose, rapidly restoring coagulation, showcasing a unique pharmacokinetic intervention.

Correct Answer: B

Rationale: Osmotic pressure (B) is a colligative property, depending on the number of solute particles in solution, not their identity (e.g., NaCl in IV fluids). Solubility (A) is a chemical property, varying with solute type. H⁺ concentration (C) defines pH, not colligative. Dissociation (D) affects particle number but isn't the property itself. Miscibility (original E) is unrelated. Colligative properties (osmotic pressure, boiling/freezing point changes) are critical in pharmacokinetics, influencing drug formulation and tonicity, ensuring compatibility with biological fluids.