If the plasma concentration of a drug declines with 'first-order kinetics', this means that

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: 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.

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.