All of the following upregulate drug metabolism through hepatic enzyme induction, EXCEPT___________?
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Answer: B. Cimetidine
Explanation
Cimetidine is a well known inhibitor of hepatic cytochrome P450 enzymes, whereas rifampicin and phenobarbitone are classic inducers. Enzyme inhibitors decrease the metabolic clearance rate of coadministered drugs, frequently leading to toxic accumulation in the bloodstream. Conversely, enzyme inducers accelerate the biotransformation of substrate medications, reducing their therapeutic efficacy over time. Hepatic enzyme induction is a process where a chemical increases the metabolic activity of cytochrome P450 enzymes in the liver. Cimetidine is a histamine H2 receptor antagonist historically utilized to decrease gastric acid secretion in peptic ulcer disease. Cytochrome P450 enzymes represent a large superfamily of hemoproteins responsible for the phase one oxidative metabolism of xenobiotics.
Tetracycline antibiotics possess broad spectrum antimicrobial properties and do not function as significant hepatic enzyme inducers. Rifampicin is a potent inducer of multiple cytochrome P450 isoforms, markedly decreasing the efficacy of oral contraceptives. Phenobarbitone is a barbiturate that strongly upregulates hepatic microsomal enzymes, accelerating the clearance of numerous concurrently administered drugs.
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