Midazolam, used for procedural sedation, is distinct from diazepam in clinical pharmacokinetics primarily because:
- A Midazolam has active metabolites with half-lives exceeding 24 hours that prolong its sedation
- B Midazolam is water-soluble at acidic pH (allowing IV injection) and lipid-soluble at physiological pH (allowing rapid CNS entry), and undergoes rapid hepatic CYP3A4 hydroxylation giving a short half-life of 1.5–3.5 hours ✓
- C Midazolam undergoes primarily renal excretion unchanged, making dose adjustment necessary only in renal failure
- D Midazolam is a partial GABA-A agonist, producing less respiratory depression than diazepam
Correct answer: B. Midazolam is water-soluble at acidic pH (allowing IV injection) and lipid-soluble at physiological pH (allowing rapid CNS entry), and undergoes rapid hepatic CYP3A4 hydroxylation giving a short half-life of 1.5–3.5 hours
Explanation
Midazolam's imidazole ring undergoes ring closure at acidic pH making it water-soluble (enabling IV and IM formulations without the propylene glycol vehicle required for diazepam), then opens at physiological pH providing high lipophilicity for rapid CNS penetration. Its short clinical duration results from rapid redistribution and CYP3A4-mediated hydroxylation to an active metabolite (1-hydroxymidazolam glucuronide) that is renally excreted; the parent drug half-life is 1.5–3.5 hours compared with diazepam's 20–100 hours.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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