Rifampicin can cause a marked reduction in plasma levels andeffects of buspirone
In a randomised,study, buspirone 30mg daily was given to 10 healthy subjects, before and after they took rifampicin 600mg daily for 5 days. It was found that rifampicin reduced total AUC of buspirone by almost 90 % and reduced its peak plasma levels by 87%. The pharmacodynamic effects of buspirone were reduced accordingly (as measured by digit symbol substitution,critical flicker fusion, body sway and visual analogue scales for subjective drowsiness) (See reference number 1).
Not fully established, but it is almost certain that rifampicin induces cytochrome P450 isoenzyme CYP3A4 in gut and liver, which metabolises buspirone. Therefore metabolism and clearance of buspirone are increased.
Direct information appears to be limited to this study but it is consistent with way rifampicin interacts with many other drugs. If both drugs are used be alert for need to use an increased buspirone dosage
1. Lambert TS,Kivistö KT, Neuvonen PJ. Concentrations and effects of buspirone are considerably reduced by rifampicin. Br J Clin Pharmacol (1998) 45, 381–5.