Ketoconazole levels can be reduced by 50 to 80% by
rifampicin.
Rifampicin levels can be halved by
ketoconazole, but are possibly unaffected if the drugs are given 12 hours apart.
Wherever possible avoid concurrent use. If the combination must be used, monitor
efficacy closely, being aware that a reduced effect is highly likely. Consider increasing the doses of both drugs.