The
serum levels of
quinidine and its therapeutic effects can be markedly reduced by rifampicin. In one case
quinidine levels were reduced from 4 to 0.5 micrograms/mL.
Rifabutin is predicted to interact similarly, but probably to a lesser extent.
A
quinidine dosage increase may be necessary if
rifabutin is given. Monitor concurrent use and adjust the dose as necessary.