Acetylsalicylic acid may protect the patient by increasing fibrin gel porosity. Is withdrawing of treatment harmful to the patient?

The effect of acetylsalicylic acid in preventing cardiovascular complications is ascribed to acetylation of the enzyme cyclo-oxygenase thereby inhibiting prostaglandin synthesis. Acetylsalicylic acid, however, also acetylates fibrinogen. In the present pilot study, we investigated the permeability, i.e. porosity, of the fibrin gel in male patients with stable angina pectoris treated with this drug, before and at 1 and 2 weeks after withdrawal. Ten patients were treated with 75 mg and eight with 160 mg. The results were compared to those in seven untreated healthy controls. Bleeding times were longer during treatment and were reduced after withdrawal indicating patient compliance. Fibrin gels were more porous during treatment although there were large interindividual variations in porosity. One week after withdrawal, the porosity was reduced by 30–41% i.e. the network became tighter (75 mg group P=0.00l; 160 mg group P=0.002). The tightness was more pronounced after withdrawal than in the untreated controls. In conclusion, the protective effect of acetylsalicylic acid may be ascribed to its effect not only on platelets but also on fibrinogen. The withdrawal of acetylsalicylic acid may cause a markedly reduced fibrin gel porosity that we assume is disadvantageous in patients with cardiovascular disease.