Serum concentration of piroxicam and inhibition of platelet aggregation in patients with rheumatoid arthritis and M. Bechterew.

An open trial was conducted in 22 in-patients with classic or definite rheumatoid arthritis (RA) and 17 in-patients with M. Bechterew with the aim to investigate the effect of increasing concentrations of piroxicam in vivo on the platelet aggregation in such patients. In all patients therapy with piroxicam (10 mg/d) was started after withdrawing other non-steroidal antiinflammatory drugs. In 36 cases the daily dose of piroxicam was increased to 20 mg/d and in five cases to 30 mg/d based on clinical judgment. The platelet aggregation in platelet-rich plasma (PRP) caused by epinephrine, ADP (both 5 microM) and collagen (2 micrograms/ml) was measured at the beginning of the trial and before each dose increase. The results of the trial suggest that a significant positive correlation exists between increasing serum concentrations of piroxicam and the degree of inhibition of platelet aggregation, caused by all three platelet aggregation agonists. This action of piroxicam was most pronounced when epinephrine was used as platelet agonist.