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.
To assess the differences of infliximab (IFX) trough levels according to the dose of concomitantly used azathioprine (AZA).
All IBD patients treated with IFX (Remicade
In total, 125 patients were included, 42 pts (33.6%) on infliximab monotherapy, 83 pts (66.4%) using combined immune suppression. The respective median IFX levels according to AZA dose were as follows: group 1 (no concomitant AZA) 2.83 μg/ml (range 0-12); group 2 (AZA dose less than 1 mg/kg) 4.91 μg/ml (range 0.09-15.36); group 3 (AZA dose 1 < 2 mg/kg) 5.67 (range 0.16-16.97); group 4 (AZA dose above 2 mg/kg) 7.53 μg/ml (range 1.15-8.73). The differences in IFX trough levels between the respective groups according to AZA dose were statistically significant (p = 0.0159).
The positive effect of azathioprine on infliximab levels seems to be dependent on the dose of concomitantly used azathioprine.