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.