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Managing Drug Interactions in the Treatment of HIV-Related Tuberculosis
Predicting Drug Interactions Involving RifamycinsKnowledge of the mechanisms of drug interactions can help predict the likelihood of an interaction, if that specific combination of drugs has not been formally evaluated. The rifamycin class upregulate (induce) the synthesis of several classes of drug transporting and drug metabolizing enzymes. With increased synthesis, there is increased total activity of the enzyme (or enzyme system), thereby decreasing the serum half-life and serum concentrations of drugs that are metabolized by that system. The most common locus of rifamycin interactions is the cytochrome P450 enzyme system, particularly the CYP3A4 and CYP2C8/9 isozymes. To a lesser extent, rifampin induces the activity of the CYP2C19 and CYPD6 isozymes. The rifamycins vary in their potential as CYP450 inducers, with rifampin being most potent, rifapentine intermediate, and rifabutin being much less active. Rifampin also upregulates the synthesis of cytosolic drug-metabolizing enzymes, including glucuronosyl transferase, an enzyme involved in the metabolism of zidovudine 10 and raltegravir.
Last Reviewed: 05/18/2008 |
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Centers for Disease Control & Prevention |