The influence of azathioprine on the behaviour of blood platelets in vitro.

The influence of azathioprine on human platelets was studied in vitro. Azathioprine in a final concentration of 10(-4) M caused significant inhibition of spontaneous sedimentation and aggregation of platelets, but did not effect platelet adhesiveness or resistance to freezing and thawing. The influence of azathioprine is probably due to thioimidazole, this last being a potent stimulating agent of phosphodiesterase activity, involved in the metabolism of cyclic AMP to 5' AMP. These observations indicate that the widely used platelet function assays could be influenced by drugs. The current therapy should therefore be taken into account when the results of the tests are evaluated for clinical purposes.