A 31-year-old man is brought to the emergency department complaining of dyspnea. He has a history of asthma and has had multiple asthma attacks requiring intubation for airway maintenance. He is noncompliant with his medications prescribed for this condition. Physical examination reveals a young man in acute distress. His room air oxygen saturation is $87 \%$. In addition to administration of oxygen, immediate drug administration of albuterol should be administered by which of the following routes?

Correct Answer: A

Rationale: Inhalation (A) is the best route for immediate albuterol administration in this asthma attack, delivering the $\beta_2$-agonist directly to bronchial smooth muscle for rapid bronchodilation (within minutes), critical with $87\%$ oxygen saturation. Intranasal (B) targets nasal mucosa, not lungs. Subcutaneous (C) and sublingual (D) are slower, bypassing direct airway delivery. Topical (original E) is irrelevant. Inhalation's speed and specificity (e.g., via nebulizer or MDI) maximize efficacy in acute distress, minimizing systemic effects, essential in emergency asthma management to restore airflow and prevent intubation.

Correct Answer: A

Rationale: An agonist (A) binds receptors and mimics the endogenous ligand's response (e.g., albuterol mimics epinephrine at $\beta_2$ receptors for bronchodilation). Antagonists (B) block without response. Functional antagonists (C) oppose via different mechanisms. Partial agonists (D) and antagonists (original E) produce submaximal effects or block partially. Agonists' full activation, critical in pharmacodynamics, drives therapeutic effects, distinguishing them from blockers or partial stimulators in receptor theory.

Correct Answer: C

Rationale: $25\%$ (C) of ibuprofen remains after 4 h (t₁/₂ = 2 h). In first-order kinetics, fraction remaining = (1/2)^(t/t₁/₂) = (1/2)^(4/2) = (1/2)^2 = 0.25 = $25\%$. Options A (0\%) requires >5 half-lives, B (12.5\%) is 3 half-lives, D (50\%) is 1 half-life, E (75\%, original) underestimates decay. After 4 h (~2 half-lives), $200 \, \text{mg}$ remains from $800 \, \text{mg}$, aligning with ibuprofen's rapid clearance, relevant for timing pain relief in active patients.

Correct Answer: C

Rationale: Codeine's constipation (opioid-induced bowel dysfunction) is most similar to dizziness from nitroglycerin (C), both predictable, dose-related side effects tied to their mechanisms (μ-opioid receptor agonism vs. vasodilation). Rash (A) and anemia (B) are idiosyncratic hypersensitivities. Rhabdomyolysis (D) and urticaria (original E) are severe, less predictable. Codeine's GI stasis, common and manageable (e.g., with laxatives), mirrors nitroglycerin's hypotension, both expected pharmacodynamic outcomes, critical in patient counseling post-surgery.

Correct Answer: B

Rationale: Nicotine binds nicotinic acetylcholine receptors, opening channels for positive ions (e.g., Na⁺, Ca²⁺) to flow in (B), depolarizing neurons (e.g., in ganglia), driving addiction. Negative ions (A) hyperpolarize, opposite to nicotine's effect. Options C/D involve G-protein pathways, not ionotropic nicotinic receptors. Phospholipase C (original E) is unrelated. This excitatory response reinforces smoking, critical in cessation pharmacology (e.g., varenicline), targeting receptor stimulation to reduce cravings.