Which mechanism is most often responsible for chemical degradation?

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: 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.

Correct Answer: B

Rationale: Intravenous injection (B) gives the most rapid onset, delivering drug directly into the bloodstream, bypassing absorption (e.g., morphine in seconds). Intramuscular (A) and subcutaneous (original E) are slower due to tissue absorption. Intradermal (C) is slowest, for local effects. Peroral (D) involves GI absorption, delaying onset (e.g., 30-60 min). IV's immediacy suits emergencies, avoiding first-pass metabolism, though it risks rapid toxicity, requiring precise dosing and monitoring.

Correct Answer: B

Rationale: Creatinine clearance measures glomerular filtration rate (GFR) (B), estimating kidney filtration capacity (mL/min) via serum/urine creatinine, reflecting renal health (e.g., in drug dosing). Renal excretion rate (A) includes secretion/reabsorption. Active secretion (C) and passive absorption (D) are distinct processes. Drug metabolism (original E) is hepatic. GFR's clinical use adjusts renally excreted drugs (e.g., aminoglycosides), ensuring safety in renal impairment, a cornerstone of pharmacokinetics.

Correct Answer: C

Rationale: CYP3A4 (C) is expressed in both intestinal epithelium and kidney, metabolizing many drugs (e.g., midazolam), impacting first-pass and systemic clearance. CYP2D6 (A) is primarily hepatic. CYP1A1/2 (B) is in liver/lung, inducible by smoking. CYP2E1 (D) is hepatic, ethanol-related. No original E. CYP3A4's dual presence reduces bioavailability (e.g., cyclosporine), mediates interactions (e.g., with grapefruit juice), and is critical in drug metabolism studies, influencing dosing and efficacy.