All of the following induce liver microsomal enzymes except?

Ans. is 'a' i.e., Metyrapone Drug metabolizing enzymes The drug metabolizing enzymes are divided into two types : Microsomal These are located on smooth endoplasmic reticulum primarily in liver, also in kidney, intestinal mucosa and lungs. Examples are monooxygenase, cytochrome P450, glucronyl transferase. They catalyze most of the oxidation, reduction, hydrolysis and glucuronide conjugation. They are inducible by drugs, diet and other agencies. Non microsomal These are present in the cytoplasm and mitochondria of hepatic cells as well as in other tissues including plasma. Examples are flavoprotein oxidase, esterases, amidases and conjugases. They catalyze some oxidation and reduction, many hydrolysis and all conjugation except glucuronidation. They are not inducible but many show genetic polymorphism (acetyl transferase, pseudocholinesterase). Drugs that induce microsomal enzymes Phenobarbitone Rifampin Isoniazid Phenylbutazone DDT Carbamezepine Clofibrate Ritonavir Chronic alcohol intake Cyclophosphamide Phenytoin Glucocoicoids Chloral hydrate Griseofulvin Omeprazole Meprobamate Glutethimide Cigarette smoking Remember All Barbiturates are enzyme inducers except secobarbital, which inhibits the enzyme. Acutely, ritonavir is an inhibitor. while with chronic (repeated) administration it acts as an inducer.