Serum methadone levels can be markedly reduced by rifampicin, and withdrawal
symptoms have occurred in some patients. Similarly,
rifampicin markedly increases the
metabolism of alfentanil,
codeine, fentanyl and morphine, and reduces their effects.
Monitor concurrent use for reduced opioid effects and adjust the dose accordingly. Note that
rifabutin only appears to interact in a small number of patients, and to a lesser extent, so it may be a suitable alternative.