Which of the following antiretroviral drug combinations is accepted first-line therapy for patients with human immunodeficiency virus (HIV) infection?

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: 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.

Correct Answer: C

Rationale: Steroid hormone action involves diffusion into the cytoplasm and binding to an intracellular receptor (C), as lipophilic steroids (e.g., cortisol) cross membranes, bind nuclear receptors, and regulate gene expression. Option A describes tyrosine kinase receptors (e.g., insulin). Option B fits G-protein-coupled receptors (e.g., epinephrine). Option D involves JAK-STAT pathways (e.g., cytokines), not steroids. Option E (original) about ion channels applies to neurotransmitters. This genomic mechanism, slow but sustained, contrasts with rapid membrane receptor signaling, altering protein synthesis for effects like anti-inflammation, critical in endocrinology and pharmacology.

Correct Answer: A

Rationale: Bronchial smooth muscle (A) is not a nicotinic site; it's primarily muscarinic, responding to acetylcholine via G-protein-coupled receptors for bronchoconstriction. Nicotinic sites, ligand-gated ion channels, include adrenal medullary cells (B) for catecholamine release, parasympathetic (C) and sympathetic (original E) ganglia for autonomic transmission, and skeletal muscle (D) for contraction. Nicotinic receptors' rapid ionotropic action contrasts with muscarinic metabotropic effects, critical in pharmacology (e.g., nicotine mimics ACh at these sites). This distinction guides cholinergic drug targeting, like neuromuscular blockers (skeletal) vs. bronchodilators (smooth muscle).