The following infections have been paired with appropriate drug therapy:

Correct Answer: B

Rationale: Giardia lamblia paired with metronidazole (B) is correct, a first-line treatment for giardiasis, targeting anaerobic protozoa via DNA disruption, with high cure rates. Trypanosoma gambiense with pentamidine and suramin (A) is partially correct; pentamidine or suramin alone is used early, not combined. Taenia saginata with emetine (C) is wrong; praziquantel or niclosamide is standard. Strongyloides with mebendazole (D) is incorrect; ivermectin is preferred. Toxocara canis with pyraquantel (original E) is wrong; albendazole is used. Metronidazole's efficacy in Giardia, amoebiasis, and trichomoniasis reflects its selective anaerobic action, though GI side effects and alcohol intolerance are notable.

Correct Answer: D

Rationale: Hepatic metabolism and renal excretion are the two most important mechanisms involved (D) in terminating drug action. The liver metabolizes drugs into inactive or more excretable forms, while the kidneys filter and excrete them, as seen with many drugs like penicillin. Option A is incorrect because redistribution (e.g., thiopental moving from brain to fat) can terminate action without excretion. Option B is false; metabolism can produce lipid-soluble metabolites (e.g., morphine to morphine-6-glucuronide). Option C is wrong as some metabolites retain activity (e.g., diazepam to nordazepam). Option E (original) about distribution is a mechanism but less dominant than metabolism and excretion. These processes ensure drug clearance, balancing efficacy and toxicity, with liver and kidney function critical to dosing adjustments in disease states.

Correct Answer: A

Rationale: A pharmacological antagonist (A) best describes a drug that blocks epinephrine's action by occupying its receptors (e.g., beta-blockers like propranolol) without activation, competitively inhibiting the agonist. Partial agonists (B) activate receptors submaximally (e.g., pindolol). Physiological antagonists (C) counteract via different systems (e.g., histamine vs. epinephrine). Chemical antagonists (D) bind the agonist itself (e.g., chelators), not receptors. Noncompetitive antagonists (original E) bind irreversibly, reducing receptor availability. Pharmacological antagonism, central to receptor theory, relies on affinity without efficacy, reversing or preventing epinephrine's effects (e.g., tachycardia), a key concept in managing adrenergic overactivity in conditions like hypertension.

Correct Answer: B

Rationale: The dominant lethal test is a test of mutagenicity (B), detecting mutations in male germ cells causing fetal death or abnormalities post-mating, indicating DNA damage (e.g., from alkylating agents). Teratogenicity (A) tests developmental defects from maternal exposure during pregnancy, not paternal. Carcinogenicity (C) assesses tumor formation, requiring long-term studies. Option D is incorrect as it's specific to mutagenesis. Option E (original) is also false. Used in toxicology, this assay identifies genotoxic potential, critical for assessing reproductive risks of chemicals, though it doesn't predict teratogenesis or cancer directly.

Correct Answer: C

Rationale: Most drug receptors are proteins located on cell membranes or in the cytosol (C), such as G-protein-coupled receptors (e.g., beta-adrenergic) or intracellular nuclear receptors (e.g., steroid receptors), mediating specific drug effects. Small molecules (A) like neurotransmitters aren't receptors. Lipids (B) form membranes, not receptors. DNA (D) and RNA (original E) are targets for some drugs (e.g., chemotherapy), not typical receptors. Proteins' structural diversity enables ligand binding and signal transduction, fundamental to pharmacodynamics, distinguishing receptor-mediated effects from non-specific actions like osmosis.