Metabolism is usually facilitated by two types of enzymes: Microsomal Enzymes and Non-Microsomal Enzymes. The Microsomal Enzymes can be further classified into two types: Enzyme Inducers and Enzyme Inhibitors.
Enzyme inducers increase the metabolism of other drugs and decrease their effects. Some examples of enzyme inducers are Griseofulvin, Phenytoin, Rifampicin, Smoking, Carbamazepine, Phenobarbital, Primidone, Phenylbutazone, Chloral hydrate, and Chronic Alcohol.
Enzyme inhibitors, on the other hand, decrease the metabolism of other drugs and increase the toxicity of these drugs. Examples of enzyme inhibitors include Valproic acid, Ketoconazole, Cimetidine, Ciprofloxacin, Isoniazid, Amiodarone, Grapefruit Juice, Metronidazole, Macrolide Antibiotics, Acute Alcohol, Omeprazole and Esomeprazole, Protease Inhibitors, Non-dihydropyridine (Verapamil, Diltiazem), and Selective Serotonin Reuptake Inhibitors (SSRI).
Smoking is an enzyme inducer, and it increases the metabolism of Olanzapine, resulting in a decrease in the drug’s pharmacological effect. Therefore, if we administer Olanzapine to smoking patients, the drug dose should be increased to achieve the desired effect compared to non-smokers.
