The following are used in the prophylaxis or treatment of influenza:

Correct Answer: D

Rationale: Oseltamivir (D) is used in the prophylaxis and treatment of influenza, a neuraminidase inhibitor reducing viral spread by preventing release from infected cells, effective against influenza A and B. Amantadine (A) was used for influenza A prophylaxis/treatment, but resistance limits its role today. Palivizumab (B) prevents RSV, not influenza. Entecavir (C) treats hepatitis B, unrelated to influenza. Zanamivir (original E) also treats influenza, but D is selected. Oseltamivir's oral administration and efficacy within 48 hours of symptoms make it a primary choice in seasonal flu and pandemics, shortening illness duration and reducing complications.

Correct Answer: C

Rationale: Daunorubicin paired with cardiomyopathy (C) is correct, an anthracycline causing dose-dependent cardiotoxicity via oxidative stress and topoisomerase inhibition, common in leukemia treatment, mitigated by dexrazoxane. Etoposide (A) causes myelosuppression, not neuropathy (vincristine does). Paclitaxel (B) causes alopecia, a hallmark taxane effect. Irinotecan (D) causes diarrhea, due to cholinergic and mucosal damage. 6-Mercaptopurine with pulmonary fibrosis (original E) is incorrect; myelosuppression is typical. Daunorubicin's efficacy in acute leukemias is balanced by lifetime dose limits to protect cardiac function, monitored via echocardiography.

Correct Answer: B

Rationale: The correct answer is that the half-life is the same regardless of the plasma concentration (B). First-order kinetics implies that the rate of drug elimination is proportional to its plasma concentration, meaning a constant fraction of the drug is removed per unit time. This results in a consistent half-life, independent of the initial concentration, as seen with most drugs like aspirin. Option A is incorrect because multiple metabolic pathways can exist in first-order kinetics. Option C describes first-pass metabolism but isn't inherent to first-order kinetics. Option D is false as elimination rate depends on concentration, not administration rate. Option E (original) about vascular confinement is unrelated. This principle is foundational in pharmacokinetics, allowing predictable dosing regimens, unlike zero-order kinetics where half-life varies with concentration, as with ethanol.

Correct Answer: D

Rationale: A chemical antagonist (D) best describes an antagonist that interacts directly with the agonist, not the receptor, by neutralizing or binding it (e.g., protamine with heparin). Pharmacological antagonists (A) block receptors directly (e.g., propranolol). Partial agonists (B) bind receptors but produce submaximal effects (e.g., buprenorphine). Physiological antagonists (C) oppose effects via different receptors (e.g., epinephrine vs. histamine). Noncompetitive antagonists (original E) bind irreversibly to receptors, reducing efficacy. Chemical antagonism, a rare but specific mechanism, alters the agonist's availability without receptor interaction, critical in overdose reversal or chelation therapies, distinct from receptor-based antagonism in pharmacodynamics.

Correct Answer: C

Rationale: The correct answer is that animal testing requires the submission of histopathologic slides and specimens to the FDA (C), part of preclinical data in the Investigational New Drug (IND) application, ensuring safety evaluation. Option A is false; testing duration varies (months to years), not fixed at 3 years. Option B is incorrect; two species (e.g., rodent and non-rodent like dog) are typical, not necessarily primates. Option D is wrong; allergy prediction is poor in animals due to immune differences. Option E (original) about abbreviation for toxic agents is true but less defining. This regulatory step validates toxicity and pharmacology data, bridging preclinical and human trials.