Aspirin in the prophylaxis of coronary artery disease

Aspirin has been used for more than 100 years, but its mechanisms of action have only been understood in the past 20 years. Aspirin interferes with arachidonic acid metabolism in platelets and endothelial cells and thereby reduces thromboxane A2 and prostacyclin. It also has other mechanisms of action, including anti-inflammatory roles, protection from oxidative stress, enhancement of fibrinolysis, and suppression of plasma coagulation and platelet-dependent inhibition of thrombin generation. It has been used for primary and secondary prevention of myocardial ischemia, and for primary and secondary prevention of cerebrovascular ischemia. We review the 5 pivotal studies relating to primary prevention for cardiovascular risk and the many studies relating to secondary prevention of myocardial ischemia. We also review the utility of aspirin in primary prevention of myocardial infarction and stroke. We conclude that aspirin is one of the most potent drugs ever discovered and that its effects extend well beyond those of cycloxoxygenase enzyme inhibition. Aspirin treatment does not preclude control of underlying and comorbid conditions such as diabetes mellitus, hypertension, and dyslipidemia. For most patients, a daily dose of 325 mg is optimal. Patients must understand the potential for gastrointestinal upset and hemorrhagic complications. The utility of aspirin is greater in coronary artery disease prevention than in cerebrovascular prevention.

The effects of varying doses of aspirin on human platelet activation induced by PAF, collagen and arachidonic acid

1. The effect of increasing doses of orally administered aspirin (30-900 mg) on platelet aggregation and ATP release induced by arachidonic acid (AA), collagen and platelet activating factor (PAF) was assessed in 12 normal volunteers. 2. Aspirin ingestion was associated with a significant increase in EC50 for AA (P less than 0.0001) and collagen (P less than 0.0001) but not for PAF (P greater than 0.495) although the normal biphasic aggregation response for the latter was abolished. Maximum ATP release was reduced by aspirin for all three agonists. 3. The mean maximum degrees of inhibition of platelet aggregation induced by aspirin for AA, collagen and PAF were 100%, 48% and 21% of baseline, respectively. The corresponding mean maximum inhibition of ATP release was 100%, 63% and 57%. The minimum cumulative doses of aspirin producing these effects were 240, 240 and 90 mg for AA, collagen and PAF respectively. For collagen alone, there was a significant decrease in the degree of inhibition of aggregation between the last dose on day 1 (150 mg) and the baseline measurement on day 2. 4. Platelets from female subjects were more sensitive to collagen (P less than 0.05) and AA (P less than 0.01) stimulation compared with males. However, prior to aspirin ingestion, PAF produced a greater maximum response in platelets from females (P less than 0.02) while following aspirin ingestion PAF-induced activation was inhibited to a greater degree in females (P less than 0.02). 5. These results indicate that collagen- and PAF-induced platelet activation are only partially dependent on cyclo-oxygenase and for PAF this seems related only to the second phase of aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Cervical wound hematoma after carotid endarterectomy

Between 1974 and 1984, 1222 patients underwent carotid endarterectomy at a large community teaching hospital. Twenty-three (1.9%) of these patients required reexploration for hematoma at the endarterectomy site. We reviewed the records of these 23 patients with regard to the incidence of perioperative hypertension; the use of platelet-altering medication, heparin, protamine sulfate, and low molecular weight dextran; and the findings at reoperation. We also reviewed the records of 122 randomly selected patients who did not develop wound hematoma after carotid endarterectomy. The incidence of intraoperative and postoperative hypertension was significantly higher in the hematoma group than in the control group. The incidence of preoperative hypertension was not significantly different between the two groups. More hematoma patients received preoperative platelet-altering medication (43% versus 25%), and fewer received intraoperative protamine sulfate to reverse the effects of heparin (48% versus 66%), but these differences were not significant. This study emphasizes the importance of careful hemodynamic monitoring during and immediately after carotid endarterectomy.

A multiparametric index of platelet in vitro aggregation in cerebrovascular disease

148 patients with various forms of cerebrovascular disease (CVD) were studied by means of a multiparametric analysis of in vitro platelet aggregation, based on the following six parameters: ADP and epinephrine primary and secondary aggregation thresholds and percent maximum aggregation induced by optimal concentrations of ADP and epinephrine. These patients were assigned to four study groups, according to clinical diagnosis supported by CT scan, of transient ischemic attack and reversible neurological deficit (TIA-RIND), or completed stroke, in the presence or absence respectively of antiplatelet medical treatment at the time of the study. A statistically significant increase of the in vitro platelet aggregation was found in 44.4% of the untreated TIA-RIND patients and in 33.9% of the untreated stroke patients. However this last group showed a higher percentage of very marked hyperaggregation. Differences between the two treated study groups and controls were not significant. No difference was found in collagen- and ristocetin-induced aggregation between the patient groups and the controls.

Surprising effects of the sequential administration of pentoxifylline and low dose acetylsalicylic acid on thrombus formation

The effect of the combined oral administration of pentoxifylline (pof) and low dose acetylsalicylic acid (ASA) was evaluated with the help of the laser-induced thrombosis in rat mesenteric arterioles. Laser-induced thrombosis is inhibited in a dose-dependent way by both drugs. The administration of ASA, either simultaneously with or 1 hour prior to pof, does not show any effects in the laser model. On the contrary, the administration of pof followed 1 h later by ASA not only exhibited a significant effect but also produced a supraadditive inhibition of the laser-induced thrombus formation. Specific investigations concerning the time interval between the administration of both drugs determined that a significant effect can be achieved only after an interval of 30 to 90 minutes (principle of HWA 5112). The striking results could also be shown in diseased animals after sequential chronic administration of pof 1 h prior to ASA. HWA 5112 exhibits significant effects on laser-induced thrombus formation in the following chronic animal models: 1. adjuvant arthritic rats, 10----1 mg/kg for 21 days; 2. spontaneously hypertensive stroke-prone rats, 10----1 mg/kg three times within 24 h; 3. cholesterol-induced atherosclerosis in rabbits, 10----1 mg/kg for 14 days. The reported data clearly demonstrate that the sequential drug administration of first pentoxifylline followed 30 to 90 min later by ASA exhibits a supraadditive antithrombotic effect.

A dose-ranging study of the antiplatelet effect of enteric coated aspirin in man

Enteric coated aspirin was given to eight human volunteers in escalating doses (20, 40, 60, 80, 100 mg daily), each dose being given over two weeks. In addition, to measure the maximum effect of aspirin, each volunteer was given two single doses of 600 mg of soluble aspirin. At the end of each dosing interval we measured platelet aggregation and thromboxane formation in response to four aggregating agents and to whole blood coagulation. The doses of aspirin required to inhibit platelet aggregation in response to various stimuli were: for collagen 60-80 mg, for adenosine diphosphate and adrenaline 60 mg, and for arachidonate 40 mg. For maximum inhibition of thromboxane formation the doses were: for collagen greater than 100 mg, for adenosine diphosphate and adrenaline 60 mg, for arachidonate 80 mg, and for whole blood coagulation 100 mg. Different aspirin doses are required to inhibit the responses to different stimuli. Furthermore, for some stimuli, inhibition of thromboxane generation may require more aspirin than is required for inhibition of aggregation. The clinical implications of these findings are uncertain since we do not know which stimuli are important in arterial thrombosis in man.