Which of the following terms best describes an antagonist that interacts directly with the agonist and not at all or only incidentally, with the receptor?

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: Propranolol, a non-selective beta-blocker, blocks norepinephrine-induced bradycardia (C). Norepinephrine's beta-1 stimulation increases heart rate, but high doses trigger reflex bradycardia via baroreceptors; propranolol prevents the beta-mediated component, attenuating this. Methacholine (A), a muscarinic agonist, causes tachycardia reflexively, unaffected by beta-blockade. Nicotine (B) induces hypertension via nicotinic receptors and catecholamine release, partially beta-mediated, but not fully blocked. Phenylephrine (D) causes mydriasis via alpha-1, not beta. Propranolol's beta-adrenergic antagonism is key in managing sympathetic overactivity, though alpha effects persist.

Correct Answer: C

Rationale: Hydrolysis (C) is the most common mechanism for chemical degradation, where water cleaves bonds (e.g., esters in aspirin to salicylic acid), accelerated by pH or enzymes. Racemization (A) alters chirality (e.g., thalidomide), less frequent. Photolysis (B) degrades via light (e.g., nitroprusside), context-specific. Decarboxylation (D) removes COâ‚‚ (e.g., levodopa), rarer. Oxidation (original E) affects drugs like morphine but is less universal. Hydrolysis's prevalence in aqueous environments drives stability testing, requiring protective packaging or formulation adjustments (e.g., dry powders) to extend shelf life.

Correct Answer: B

Rationale: Rectal suppositories for adults usually weigh approximately 2g (B), a standard size ensuring sufficient drug load (e.g., glycerin for constipation) and comfortable insertion. Options A (1g) and C (3g) are smaller/larger, less common, while D (4g) and original E (5g) are excessive for routine use. This weight balances efficacy, melting time, and patient tolerance, critical in suppository design for systemic (e.g., analgesics) or local effects, with cocoa butter or synthetic bases adjusting to body temperature for release.

Correct Answer: C

Rationale: Sorbitan esters (spans) (C) are nonionic surfactants used as synthetic emulsifiers, stabilizing emulsions (e.g., creams) by reducing surface tension without ionization. Tragacanth (A) is a natural gum, not synthetic. Sodium lauryl sulphate (B) is anionic, not nonionic. Option D is a placeholder. No original E exists. Spans' lipophilic nature (low HLB) aids oil-in-water emulsions, enhancing drug delivery and stability, widely used in topical and oral pharmaceuticals for their versatility.