Hydrolysis reaction are involved with the metabolism of following drugs, except

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Chapter 12 principles of pharmacology Questions

Question 1 of 5

Hydrolysis reaction are involved with the metabolism of following drugs, except

Correct Answer: B

Rationale: Diazepam (B) does not undergo hydrolysis; it's metabolized by CYP450 oxidation and glucuronidation (e.g., to nordazepam). Procaine (A), aspirin (C), and lidocaine (D) hydrolyze via esterases (e.g., procaine to PABA), cleaving ester bonds. No original E. Hydrolysis, a phase I reaction, increases polarity for excretion, but diazepam's oxidative path prolongs its action, impacting its use as a long-acting anxiolytic, distinct in metabolism profiles.

Question 2 of 5

A 29-year-old man presents to his primary care physician complaining of dysuria, urgency, and painful ejaculation. The patient has a past medical history of allergic rhinitis. Physical examination reveals a tender prostate. The patient is given a prescription of sulfamethoxazole to be taken daily (q 12 h) for 30 days. The half-life is 12 h. How long will it take for the medication to reach $90 \%$ of its final steady state level?

Correct Answer: D

Rationale: It takes 40 h (D) for sulfamethoxazole (t₁/₂ = 12 h) to reach $90\%$ steady state. Steady state is ~4-5 half-lives; $90\%$ occurs at ~3.3 half-lives (derived from 1 - 1/2^n = 0.9, n ≈ 3.32). Thus, 3.32 × 12 h ≈ 39.84 h, rounding to 40 h. Options A (10 h), B (20 h), and C (30 h) are too short; E (50 h) overshoots. This first-order kinetic principle ensures therapeutic levels for prostatitis, with q12h dosing matching t₁/₂, optimizing efficacy while minimizing resistance in chronic infections.

Question 3 of 5

A 40-year-old man is brought to the emergency department after suffering a cardiac arrest while in a shopping mall. His blood pressure is $70 / 40 \mathrm{~mm} \mathrm{Hg}$ and his pulse is 40 beats/minute. He is given a dose of intravenous epinephrine. Which of the following reactions is necessary to induce a biologic response of increased heart rate?

Correct Answer: B

Rationale: Drug-receptor complex formation (B) is necessary for epinephrine to increase heart rate. Epinephrine binds $\beta_1$-adrenergic receptors on cardiac myocytes, activating Gs proteins, increasing cAMP, and enhancing contractility/chronotropy. Detrusor contraction (A) is bladder-related. Hepatic oxidation (C) is metabolism, not action. Renal contraction (D) or splanchnic stimulation (original E) are unrelated. This receptor interaction, critical in cardiac arrest, drives rapid hemodynamic response, a pharmacodynamic cornerstone for catecholamines in emergencies.

Question 4 of 5

A 67-year-old hospitalized patient with a deep venous thrombosis of the left calf and pulmonary embolism is currently on intravenous heparin on an hourly drip. Unfortunately, because of a calculation error, the heparin drip is running at 100 times the rate it should be running at. Protamine sulfate is immediately given intravenously. This agent works by which of the following mechanisms of action?

Correct Answer: B

Rationale: Protamine sulfate acts as a chemical antagonist (B), binding heparin (a negatively charged anticoagulant) via ionic interactions, neutralizing it without receptor involvement, reversing overdose effects (e.g., bleeding). Agonist (A) activates receptors. Functional agonist (C) mimics via different pathways. Partial agonist (D) or antagonist (original E) involve receptors. Protamine's direct chemical neutralization, critical in emergencies, restores clotting rapidly, a unique non-receptor mechanism in pharmacology, essential for managing heparin toxicity.

Question 5 of 5

An 80-year-old male nursing home resident is hospitalized on a morphine drip to control pain for his terminal metastatic pancreatic cancer. Morphine undergoes phase I and phase II metabolism in the liver as well as being metabolized by other enzymes. Some of these metabolic reactions decrease with age. Which of the following metabolic reactions is likely still intact in this patient?

Correct Answer: A

Rationale: Glucuronidation (A) is likely intact in this elderly patient. This phase II reaction, conjugating morphine to morphine-6-glucuronide via UGT enzymes, declines less with age than phase I reactions (e.g., CYP450 oxidation), which slow significantly. Hydrolysis (B), oxidation (C), reduction (D), and unmasking (original E) are phase I, more affected by aging liver function. Morphine's active metabolite from glucuronidation retains potency, critical in pain control, with preserved conjugation ensuring clearance despite age-related hepatic decline, a key consideration in geriatric pharmacology.

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