Demonstration of a Plasmatic Cofactor Different from Fibrinogen Necessary for Platelet Release by ADP and Adrenaline

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.

Effect on platelet aggregation of oral administration of 10 non-steroidal analgesics to humans

Platelet aggregation was investigated in platelet-rich plasma from normal volunteers before and at various times after intake of 10 analgesic drugs. The drugs used were aspirin, piroxicam, naproxen, indomethacin, diclofenac, ibuprofen, diflunisal, paracetamol and oxyphenbutazone. Aggregation of the platelets was induced by adrenaline or ADP and the first and second waves of aggregation were evaluated. It was found that no drug exerted any effect on the first wave of aggregation. The second wave of aggregation was abolished by aspirin that produced a long-lasting effect for 5-8 d. Piroxicam also abolished the second wave of aggregation and this effect persisted on the 2 following d. Naproxen was normalized in half of the volunteers on the 2nd d. The inhibition caused by indomethacin and diclofenac was corrected on the 2nd d. Ibuprofen and diflunisal produced a definite but short-term effect. The effect of salicylic acid was weak. Paracematol and oxyphenbutazone did not affect platelet aggregation.