Rifampicin increases oral clearance of fexofenadine, but theclinical significance of this is unclear.
Clinical evidence,mechanism, importance and management
A single 60mg dose of fexofenadine was given to 24 healthy subjects 2 days before and on last day of a 6-day course of rifampicin 600mg daily. The oral clearance of fexofenadine was increased 1.3-to 5.3-fold,with no effect on renal clearance or half-life. This was thought to be due to effect of rifampicin on P-glycoprotein, which is involved in uptake of fexofenadine.(See reference number 1) The clinical significance of this interaction is unclear, but until more is known it would seem prudent to monitor efficacy of fexofenadine if it is given in combination with rifampicin.
1. Hamman MA,Bruce MA, Haehner-Daniels BD, Hall SD. The effect of rifampin administration on the disposition of fexofenadine. Clin Pharmacol Ther (2001) 69, 114–21.