Pharmacokinetic interaction of antimicrobial agents with levomethadon in drug-addicted AIDS patients.

Morphine and its derivatives are metabolized by the liver microsomal enzyme system with a high first-pass effect after oral application. In four of 44 HIV-infected i.v. drug abusers who participated in a levomethadon maintenance program, we observed sustained symptoms of under-dosage and loss of effect of there to fore well-tolerated substitution therapy during rifampin treatment or therapy with zidovudine or fucidic acid. As a pharmacological model substance for cytochrome p 450 enzymes, measurement of antipyrine in serum by high pressure liquid chromatography revealed induction of cytochrome p 450 isoenzymes. The half-life of antipyrine decreased (patient 1 from 11.3 to 8.4 h and patient 2 from 10.7 to 7.6 h after rifampin, patient 3 from 12.2 to 8.6 h after fucidic acid, and patient 4 from 10.6 to 8.6 h after zidovudine). In i.v. drug abusers on levomethadon maintenance programs, adjustment of the levomethadon dosage may be necessary when specific therapy for HIV infection and associated diseases requires the use of drugs known to be potent inducers of the liver microsomal enzyme system.