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The page below is a sample from the LabCE course Drug Metabolism. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Enzyme Induction, continued

Inducers of CYP1A2 will accelerate the metabolism of some tricyclic antidepressants, haloperidol, theophylline, and several other important drugs. Inducers of CYP2E1 will accelerate the metabolism of acetaminophen. Numerous drugs are metabolized by CYP3A4. Therefore substances that induce CYP3A4 will accelerate the metabolism of a vast array of drugs, including calcium channel blockers, cyclosporine, tacrolimus, cannabinoids and opiates.
Rifampicin, an antibiotic used to treat tuberculosis, leprosy, and other serious bacterial infections, is considered to be the most powerful inducer of cytochrome P450 enzymes. It induces CYP3A4/5, CYP2C19, CYP2C9, CYP2C8, CYP2B6, and CYP2A6. Other strong inducers are the anticonvulsants phenytoin and carbamazepine. Phenytoin induces CYP3A4/5 and CYP1A2. Carbamazepine induces CYP3A4/5 and CYP2C19, causing increased metabolism of phenytoin resulting in decreased serum concentration and reduced effect.
Primidone is an anticonvulsant. The active metabolites of primidone, phenobarbital and phenylethylmalonamide (PEMA), are also anticonvulsants. Primidone is much less toxic in overdose than phenobarbital. Primidone accelerates the metabolism of many other pharmaceuticals because it is an inducer of metabolic enzymes in the liver.
Primidone, carbamazepine, phenobarbital, and phenytoin are among the most potent hepatic enzyme-inducing drugs in existence. This enzyme induction occurs at therapeutic doses. In fact, people taking these drugs have displayed the highest degree of hepatic enzyme induction on record.
CYP2D6 is generally considered non-inducible. However, there is some evidence to suggest that rifampicin and dexamethasone have an inducing effect on this enzyme.