Positive pharmacokinetic effect of azathioprine co-medication on infliximab trough levels is dose-dependent.

Background: Thiopurines seem to have positive effect on the pharmacokinetics of anti-tumor necrosis factor biologics. It has been suggested that a reduced dose of thiopurines is sufficient to achieve this synergism.

Aims: To assess the differences of infliximab (IFX) trough levels according to the dose of concomitantly used azathioprine (AZA).