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Chapter 4: Drug Metabolism

You are planning to treat chronic major depression in a 35-year-old patient with recurrent suicidal thoughts. She has several comorbid conditions that require drug therapy, including rifampin for tuberculosis and amiodarone for arrhythmia. You are concerned about drug interactions caused by changes in drug metabolism in this patient.

Drug metabolism in humans usually results in a product that is

(A) Less lipid soluble than the original drug

(B) More likely to distribute intracellularly

(C) More likely to be reabsorbed by kidney tubules

(D) More lipid soluble than the original drug

(E) Less water soluble than the original drug

Biotransformation usually results in a product that is less lipid-soluble. This facilitates elimination of drugs that would otherwise be reabsorbed from the renal tubule. The answer is A.

You are planning to treat chronic major depression in a 35-year-old patient with recurrent suicidal thoughts. She has several comorbid conditions that require drug therapy, including rifampin for tuberculosis and amiodarone for arrhythmia. You are concerned about drug interactions caused by changes in drug metabolism in this patient.

If therapy with multiple drugs causes induction of drug metabolism in your depressed patient, it will

(A) Be associated with increased smooth endoplasmic reticulum

(B) Be associated with increased rough endoplasmic reticulum

(C) Be associated with decreased enzymes in the soluble cytoplasmic fraction

(D) Require 3–4 months to reach completion

(E) Be irreversible

The smooth endoplasmic reticulum, which contains the mixed-function oxidase drug-metabolizing enzymes, is selectively increased by inducers. The answer is A.

Which of the following factors is likely to increase the duration of action of a drug that is metabolized by CYP3A4 in the liver?

(A) Chronic administration of rifampin during therapy with the drug in question

(B) Chronic therapy with amiodarone

(C) Displacement from tissue-binding sites by another drug

(D) Increased cardiac output

(E) Chronic administration of carbamazepine

Rifampin and carbamazepine can induce drug-metabolizing enzymes and thereby may reduce the duration of drug action. Displacement of drug from tissue may transiently increase the intensity of the effect but decreases the volume of distribution. Amiodarone is recognized as an inhibitor ...

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