Platelet aggregation and plasma levels of acetylsalicylic acid in stroke patients on long-term treatment with an enteric-coated aspirin formulation.

Enteric-coated formulations of acetylsalicylic acid (ASA) should be advantageous in prophylaxis after stroke because they cause fewer gastrointestinal side effects. However, the absorption of unchanged ASA and the effectiveness of these formulations have been questioned, which prompted the present investigation. Fourteen elderly stroke patients on long-term medication with enteric-coated ASA 1.5 g daily and four patients on placebo were studied. When tested with arachidonic acid platelet aggregation was completely inhibited in all ASA subjects whereas it was normal in the controls. Plasma samples, drawn every 1/2 h for 6 h after tablet intake, were analyzed by HPLC. The presence of ASA was short lasting with a mean peak concentration of 55 mumol/l reached after 2-3.5 h. Salicylic acid (SA) appeared later, having a mean peak value of 591 mumol/l after 2.5-6 h. Thus, absorption of ASA as well as inhibition of platelet aggregation were confirmed during long-term medication with enteric-coated ASA.