Pharmacology of antiplatelet drugs and clinical trials on thrombosis prevention: a difficult link

Prevention of Reocclusion After Prosthetic Bypass Operations in the Femoro-Popliteal Region: A Comparative Study of Pentoxifylline Versus Acetylsalicylic Acid

One hundred eighteen patients (88 males, 30 females, mean age 67.2 years, age range 42 to 87 years) with successfully performed synthetic prosthetic by pass operations in the femoro-popliteal area were submitted in an open random ized study of two groups of 59 subjects to oral treatment by 400 mg pentoxifylline in special patented slow-release formulation or 500 mg ASA tid from two days before operation until twelve months after operation (with par enteral administration of both drugs on the day of surgery and two days after surgery). Effectiveness of prevention of reocclusion was assessed by patency rates and drug tolerability.

The examinations (clinical status, pulse palpation, Doppler-pressure mea surement, arteriography) were carried out before and on days five or six after operation, and also after three, six, nine, and twelve months of the follow-up period.

The life table analysis disclosed no significantly different patency rates (75% for the pentoxifylline-treated group and 74% for the ASA cohort).

A significantly superior tolerability was found in the patients treated with pentoxifylline, 6 patients (10%) reporting adverse reactions as compared with 33 (56%) in the ASA-treated group. The side effects consisted mostly of gastric upset, dizziness, and gastric hemorrhage. The medication was discontinued in 6 patients on pentoxifylline and 12 on ASA.

Acetylsalicylic Acid in migraine with aura prevention - a retrospective study

In a retrospective study we evaluated the efficacy and tolerability of Acetylsalicylic Acid (ASA), an antiplatelet drug, in the prophylactic treatment of migraine with aura (MA). We reviewed the charts of 203 patients suffering from MA according to the ICHD II criteria, attending to Turin University Headache Centre. 95 subjects (46.8%) were treated with ASA at low dose, 108 (53.2%) with other prophylactic therapies normally used for migraine for a period that ranged from at least 4 months to 194 months. Eighty-four patients (88.4%) treated with ASA referred positive results, while only 64 patients (59.3%) who underwent other prophylactic treatments did (p < 0.001). The attacks' frequency of patients treated with ASA decreased significantly from 3.83±1.57 pre-treatment to 1.38±0.87 after treatment (p<0.001). Aura duration was markedly reduced from 36.21±19.80 pre-treatment to 22.0±15.5 after treatment (p<0.001). ASA was well-tolerated. ASA is a safe drug with minor possible side effects that can be routinely used when prophylactic treatment of MA is required.

Current concepts about inhibition of platelet aggregation

One hundred twenty-seven years after Professor Giulio Bizzozero described the blood particle that has come to be known as the platelet, antiplatelet therapy has revolutionized the treatment of cardiovascular disease. Platelet function testing, introduced in 1962 with the advent of Born's aggregometer, heralded a renaissance in platelet research and provided a platelet function test to study platelet reactivity in vitro to help the diagnosis of bleeding disorders. More devices to test platelet function have emerged since, and these are now being applied mainly to assess antiplatelet drug efficacy in thrombotic disorders. Although this may be a logical use for platelet function tests, the data are replete with contradictions, and there is a lack of both consensus and standardization of the methodology. As a result, the clinical validity of platelet function results to monitor response to antiplatelet drugs has yet to be established.

Aggrenox((R)) versus other pharmacotherapy in preventing recurrent stroke

Stroke is the third leading cause of death in the US with recurrent events a high likelihood in those who survive an initial event. The long-term goal of therapy is to prevent the recurrence of stroke and other atherosclerotic events. Aspirin has been the first-line agent for stroke prevention for a long time. As new antiplatelet agents have been introduced, their role in the secondary prevention of stroke remains to be defined. In particular, the role of the combination of aspirin and modified-release dipyridamole (Aggrenox, Boehringer Ingelheim Corp.), the newest product, in the secondary prevention of stroke, remains unknown. The purpose of this manuscript is to review the evidence of these antiplatelet agents in the secondary prevention of stroke and arrive at a conclusion specifically regarding the role of Aggrenox. Clinical studies which examined stroke as a single primary outcome or as one event in a combined primary outcome will be reviewed.

Lipid peroxidation products and changes in phospholipid composition induced by indobufen in diabetic platelets

Indobufen is an antiaggregatory drug which first of all inhibits platelet aggregation by interfering with cyclooxygenase enzymes in platelets. We have investigated the influence of indobufen (200 mg twice daily for 10 days) on platelet lipid peroxidation and phospholipid metabolism in diabetic patients. The production of lipid peroxidation products was significantly lower after drug treatment. Indobufen administration, however, had no influence on the fatty acid composition of platelet phospholipids.

Low-dose aspirin in the prevention of preeclampsia and fetal growth retardation: rationale, mechanisms, and clinical trials

Preeclampsia is characterized by a functional imbalance between vascular prostacyclin and thromboxane A2 production. On the basis of the hypothesis that preeclampsia is at least partially caused by an increase in thromboxane A2, some studies attempted to correct this pathologic condition by pharmacologic manipulation with low-dose aspirin. The current literature suggests that the use of low-dose aspirin during pregnancy is safe with regard to congenital anomalies and fetal, neonatal, and maternal cardiovascular physiologic state and hemostasis. Aspirin at least partially corrects the pathologic increase in angiotensin II sensitivity that precedes the clinical development of preeclampsia. In addition, some clinical trials have demonstrated that low-dose aspirin is effective in reducing the incidence of preeclampsia and/or fetal growth retardation in selected high-risk women. Currently, large clinical trials are in progress to evaluate the effectiveness and side effects of the use of low-dose aspirin in preventing preeclampsia and/or fetal growth retardation. Until these studies have been completed, it will remain unclear whether antiplatelet therapy, such as low-dose aspirin, should be adopted for the prevention of either preeclampsia or fetal growth retardation.

Reocclusion prophylaxis with dipyridamole combined with acetylsalicylic acid following PTA

After primary successful PTA, 199 patients were randomized into one of three treatment groups, namely, placebo or a combination of 75 mg dipyridamole with either 330 mg (high dose) or 100 mg (low dose) acetylsalicylic acid (ASA) tid. The duration of treatment was six months. Of the 199 patients admitted to the study, 156 completed the six-month trial period. Not all patients had a second angiogram, and in these cases clinical findings were used in the evaluation. Evaluation of the combined angiographic and clinical results showed improvement or no deterioration in 37% of patients in the placebo group compared with 49% in the low-dose and 61% in the high-dose ASA groups respectively. The only statistically significant difference observed was between the placebo group and the group treated with dipyridamole and high-dose ASA (p = 0.01). This difference remained statistically significant at p = 0.039 if only the angiographic findings were considered for group comparison. It cannot, however, be concluded from this study that 75 mg dipyridamole in combination with 100 mg ASA tid is more effective in preventing reocclusion after PTA than in combination with 330 mg ASA tid.

Response of thromboxane B2, malondialdehyde and platelet sensitivity to 3 weeks low-dose aspirin (ASA) in healthy volunteers

To examine the effects of low-dose aspirin thromboxane B2 (TXB2), malondialdehyde (MDA) and platelet sensitivity to prostaglandin I2 (PGI2) have been measured in a total of 18 healthy volunteers. They were randomly assigned to 3 groups, 6 volunteers each, receiving either 1, 10 or 20 mg ASA orally a day for 3 weeks in a double-blind fashion. In order to assess the time course of ASA-induced changes, blood was drawn before, 1 hour and 2, 3, 5, 7, 9, 12, 14, 16 and 21 days after the first drug-intake. Serum-TXB2 was depressed time- and dose-dependently, after 1 mg daily to about 60%, after 10 mg to about 30%, after 20 mg to about 5% of controls. MDA-formation and conversion of exogenously added arachidonic acid (AA) to TXB2 also dropped significantly, (p less than 0.01), the extent depending on the ASA-dosage administered. The drop in MDA- and TXB2-values in the 3 groups correlated with r = 0.98, 0.94, 0.98, respectively. The platelet sensitivity during 20 and 10 mg ASA-administration did not change at all, whereas a significant increase (p less than 0.01) in platelet sensitivity during treatment with 1 mg ASA was observed.

Effects and interaction studies of triflusal and other salicylic derivatives on cyclooxygenase in rats

Triflusal (TR) is a new salicylic acid derivative used clinically as an antiplatelet drug. Both aspirin (ASA) and TR inhibit platelet cyclooxygenase but the effects of these drugs are different. TR (0.5-2 mM) strongly inhibited platelet aggregation and malondialdehyde formation induced by arachidonic acid. The IC50 was 0.8 mM for TR and less than 0.1 mM for ASA. Deacetylated compounds, salicylic acid (SA) and HTB (the main metabolite of TR) were apparently competitive and reversible inhibitors of cyclooxygenase and HTB was 15 times more potent than SA. They did, however, partially prevent the inhibitory effects of ASA and TR in vitro. A similar effect was observed ex vivo in rats treated with HTB (100 mg/k i.p.) before TR or ASA (20 and 5 mg/kg i.v., respectively). Moreover, TR at 10 and 20 mg/kg i.v., inhibited thromboxane production by more than 50% while its effect on vascular cyclooxygenase was negligible. These findings indicated that TR is a weaker inhibitor of cyclooxygenase than ASA, and that HTB interferes with the effect of TR and ASA, despite the fact that HTB is a more potent reversible inhibitor than SA with probably a higher affinity for this enzyme.

Low-dose acetylsalicylic acid (ASA) plus dipyridamole versus dipyridamole alone in the prevention of stroke in patients with reversible ischemic attacks

A total of 243 patients who had reversible ischemic attacks (RIA) were submitted to clinical trial to determine whether dipyridamole (400 mg/day) (D) or aspirin (100 mg/48 hours) + dipyridamole (300 mg/day) (ASA + D) would produce significant reduction in the subsequent occurrence of RIA and completed stroke. One hundred and fifteen were selected for Group ASA + D and 71 were treated with dipyridamole only. The treatment groups were similar in relation to age, sex, risk factors, duration and presumed vascular territory of RIA, incidence of alterations of arterial supra-aortic trunks, cerebral infarct (CT scan), and platelet function. Patients were followed for a mean time of 21 months. At the end of the study, 21.7% of the ASA + D group and 19.7% in the D group had suffered new episodes of RIA or completed stroke (p = 0.88). Frequency of stroke (reversible ischemic neurologic deficit or completed stroke) was 7.8% in the ASA + D patients and 9.8% in the D patients (p = 0.83). Subgroup analysis did not show significant differences either. It is concluded that ASA + D has no significantly greater beneficial effect than that observed with D alone in the secondary prevention of atherothrombotic cerebral ischemia. However, a statistical Type II error cannot be excluded by the reduced number of recurrences.

Relevance of platelet factor four (PF4) plasma levels in multiple sclerosis

In order to study the role of platelets in Multiple Sclerosis (MS) we assessed, in a group of patients during a quiescent phase of the disease, the plasma levels of beta-thromboglobulin (beta-TG) and platelet factor four (PF4) both in absence of treatment and during administration of aspirin (ASA) at the dose of 50 mg/daily. In the MS patients studied, the basal plasma levels of beta-TG and PF4 were significantly higher than in control subjects. The increase in the beta-TG plasma levels occurred independently of the age, sex and severity of the disease, whereas the modification in the PF4 plasma levels was significantly correlated with the severity of the disease. Administration to the patients of ASA, at the dose that does not affect prostacyclin production, determined a decrease of beta-TG in 77% of the patients. Mean PF4 plasma levels remained unchanged. These results suggest that PF4 in the plasma of MS patients may originate not only from the platelets but also from the mast cells following platelet aggregating factor (PAF) stimulation and immunocomplex formation.

Platelet aggregation and platelet-inhibiting drugs

Platelet function may cause a progression of central gray matter damage after cerebrospinal hemorrhage or trauma because of the thrombotic occlusion of injured vessels or a vasospasm induced by extravasated blood. It has therefore been suggested that antiplatelet drugs could limit the extent of the neurological lesions produced by a spinal trauma. In view of this possibility, the hemostatic functions of platelets and the mechanism of action of antiplatelet drugs are briefly reviewed.

Antiaggregative aspirin dosage at the affected vessel wall

The present study, using patients with Takayasu's disease (pulseless disease), characterized by segmentally affected arterial lesions and stenotic conditions with a nonspecific inflammatory morbid condition, was designed to assess whether or not a low dose of aspirin can practically exert its preventive effect against the aggregation of platelets that have just passed along a rough-surfaced arterial wall. Twenty Japanese women with Takayasu's disease were selected under the following criteria: A unilateral upper extremity was angiographically confirmed to be affected with the disease, while the contralateral limb was almost normal. Systolic blood pressure on the affected side was almost half that on the nonaffected side. The patients showed neither a positive CRP nor an accentuated ESR. In these patients, mean plasma levels of TXB2 and 3 microM ADP-induced platelet aggregation in blood obtained from the affected side were 156.5 +/- 17.7 pg/ml, and 59.5 +/- 6.0%, respectively, which were significantly high as compared with 104.5 +/- 17.6 and 41.7 +/- 8.8%, respectively, in samples from the nonaffected side. Forty and eighty mg of aspirin per day administered to two randomly composed groups, respectively, showed an improvement in platelet aggregability and TXB2 levels on the nonaffected side. In the affected limbs, though 80 mg/day led to significant decreases in TXB2 levels (108.0 +/- 7.8 pg/ml, p less than 0.05) and platelet aggregability (21.3 +/- 7.6%), the 40-mg regimen showed no significant reductions (134.6 +/- 9.4 pg/ml, 35.6 +/- 17.1%). Plasma levels of 6-keto PGF1 alpha revealed no differences between 40- and 80-mg regimens, or between before and after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Low dose aspirin does not prevent fibrinolytic response to venous occlusion

Interest in the antithrombotic potential of low-dose aspirin is based on its ability to inhibit thromboxane (Tx)A2-related platelet function with concomitant sparing of vascular prostacyclin (PGI2) production. The aim of this study was to investigate the effect of low-dose aspirin (20 mg daily for 7 days) on the increase in fibrinolytic activity in healthy volunteers after venous occlusion. We also tested the effect of high-dose aspirin (650 mg X 2), of salicylate (569 mg X 2) and of indobufen (200 mg X 2), a new cyclo-oxygenase inhibitor unrelated to salicylates. Low-dose aspirin reduced serum TxB2 generation by about 90% and suppressed arachidonate-induced platelet aggregation. In contrast, fibrinolytic activity, measured by the euglobulin lysis area and the euglobulin lysis time, was not significantly affected. Both high-dose aspirin and indobufen significantly inhibited TxB2 generation and the rise in fibrinolytic activity induced by venous occlusion, without affecting the pre-occlusion values. Salicylate did not significantly affect any parameter studied. Besides offering a favorable solution to the "aspirin dilemma" related to the TxA2/PGI2 balance, low-dose aspirin might leave intact the fibrinolytic capacity of the vessel wall.

Antithrombotic therapy in children and adolescents

This report documents our experience with long term antithrombotic therapy (acenocoumarol plus aspirin) in 31 children and adolescents, from 5 months to 16 years of age. The valves replaced were mitral in 20 patients, aortic in 4, mitral-aortic in 4 and tricuspid in 3; the overall follow-up time was of 1336 months. Anticoagulant requirement in each children was not in correlation with age, but a significant increase (p less than 0.01) was found in association with sexual development. Our total incidence of embolic episodes was 1.49/1000 patient-months. The embolic incidence on adequate anticoagulated patients was 0.74/1000 patient-months and 93.7% of all patients were free of thrombo-embolic accidents up to 96 months of follow-up. Minor haemorrhage in relation to an excess of anticoagulant was 1.49/1000 patient-months. There has been only one major bleeding episode associated with severe sepsis, with an incidence of 0.74/1000 patient-months. No major difficulties were found in the management of anticoagulant treatment and its association with antiplatelet drugs in children.

The effects of different doses of some acetylsalicylic acid formulations on platelet function and bleeding times in healthy subjects

In an attempt to find the most appropriate dose and formulation(s) of acetylsalicylic acid (ASA) for thrombosis prophylaxis, healthy volunteers were given doses of ASA for 1 wk daily ranging from 50 to 3900 mg as either Aspro-Clear (soluble), Astrix (enteric coated pellets) or Ecotrin (enteric coated tablets). Platelet function and bleeding times were monitored. All doses of ASA significantly inhibited platelet function (p less than 0.05) and increased bleeding times (p less than 0.05) relative to control values. Irrespective of the formulation, maximum increases in bleeding time and platelet dysfunction were obtained with daily doses of about 100 mg, and no further changes were observed with higher doses.

Hypotensive and antiplatelet actions of motapizone depend on dose and time after ingestion

Single doses of motapizone 1 to 10 mg were given to 12 healthy subjects. Before and up to 8 h after each dose the blood pressure and heart rate were measured, as well as thrombocyte aggregation "ex vivo" with collagen, ADP and adrenaline. Motapizone produced a dose-dependent reduction in diastolic blood pressure and an increase in heart rate. These effects were demonstrated with individual variations after 1 to 3 mg and as a rule they were very marked after more than 6 mg. With the highest dose (mean 7.7 +/- 2.3 mg) the diastolic pressure fell by an average of 23% 1 h after medication as compared to with the baseline values. At the same time there was marked inhibition of thrombocyte aggregation, which also became apparent after about 3 mg and increased in proportion to the dose. The inhibition of aggregation peaked after 2 h and had disappeared within 8 h. The inhibition of ADP-induced aggregation was particularly marked.

Pharmacology of platelet inhibition in humans: implications of the salicylate-aspirin interaction

The current dispute over the effects of "low" vs "high" doses of aspirin should take into consideration the pharmacokinetics of this drug. In fact, different pharmaceutical formulations of aspirin may deliver little or no aspirin to the systemic blood. This was the case, for instance, in healthy volunteers taking 320 mg of compressed aspirin or 800 mg of enteric-coated aspirin. In all instances thromboxane B2 generation in serum was fully inhibited. Platelet cyclooxygenase might therefore be effectively acetylated by exposure to aspirin in the portal circulation, whereas vascular cyclooxygenase could be spared. Thus aspirin formulations ensuring complete first-pass deacetylation should be sought rather than "low" or "high" doses of unspecified aspirin formulations. Regardless of the type and dose of aspirin administered, salicylate is formed and accumulates in the circulation. It may antagonize the effects of aspirin on cyclooxygenase, at least in acute conditions. As an example, after administration of 1 g of salicylate to healthy volunteers, when plasma levels of the drug were about 75 micrograms/ml, the effect of 40 mg iv aspirin (given 40 min later) on platelet cyclooxygenase and aggregation was significantly diminished. In contrast, in patients undergoing saphenectomy, the same dose of salicylate (1 g) gave plasma drug levels of about 25 micrograms/ml; salicylate was unable to prevent the inhibitory effect on platelets of 40 mg iv aspirin (given 1 hr later) but did act on vascular prostacyclin. Thus the combination of salicylate with aspirin at an appropriate dose and blood level ratio may result in almost complete dissociation of the drug's effect on platelets and vessels in man.(ABSTRACT TRUNCATED AT 250 WORDS)

The low dose aspirin controversy solved at last?

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Cerebral platelet thromboembolism and thromboxane synthetase inhibition

Platelet aggregating sodium arachidonate was slowly infused into the internal carotid artery (1 mg, 100 microliters, 1 microliter/s) of nitrous oxide anesthetized rats. The electroencephalographic activity recorded by a Cerebral Function Monitor from the injected hemisphere was reduced within minutes. The somatosensory evoked responses to contralateral electrical stimulation of the whisker area were eliminated on the same side in most cases when measured five and fifteen minutes after the infusion. The brain was frozen in situ with liquid nitrogen after fifteen minutes. Regional tissue analysis showed ipsilateral derangement of the cerebral energy state and increased lactate levels. Pretreatment with the platelet antiaggregating thromboxane synthetase inhibitor OKY-1581 (Sodium-3-4-(3-pyridylmethyl)phenyl-2-methyl-acrylate), 30 mg/kg i.v., fifteen minutes before the sodium arachidonate infusion prevented cerebral energy failure and elimination of the sensory evoked responses.

Effects of platelet-modifying drugs on arterial thromboembolism in baboons. Aspirin potentiates the antithrombotic actions of dipyridamole and sulfinpyrazone by mechanism(s) independent of platelet cyclooxygenase inhibition

To resolve questions of drug actions, efficacy, and interactions for platelet-modifying agents used clinically, we have compared the relative capacities and mechanisms of aspirin, dipyridamole, sulfinpyrazone, and dazoxiben to prevent arterial thromboembolism in a baboon model. In 136 studies the agents were given twice daily by oral administration both singly and in combination. The antithrombotic efficacy of a given therapy was determined by its capacity to interrupt steady-state platelet utilization induced by thrombogenic arteriovenous cannulae. When given alone, dipyridamole and sulfinpyrazone reduced the rate at which platelets were utilized by thrombus formation in a dose-dependent manner with essentially complete interruption by dipyridamole at 10 mg/kg per d. In contrast, neither aspirin (2-100 mg/kg per d) nor dazoxiben (20-100 mg/kg per d) decreased cannula platelet consumption detectably despite the striking reduction in the capacity of platelets to produce thromboxane B2. However, aspirin, but not dazoxiben, potentiated the antithrombotic effects of dipyridamole and sulfinpyrazone in a dose-dependent fashion without changing the pharmacokinetics for any of the agents. Complete potentiation required aspirin at 20 mg/kg per d to be given with each dose of dipyridamole. Because dazoxiben's blockade of platelet thromboxane A2 production was not associated with antithrombotic potentiation, and because complete potentiation by aspirin required a dose that fully inhibited vascular production of prostaglandin I2 (PGI2), we conclude that aspirin's potentiating effect on dipyridamole is independent of PGI2 production or inhibition of thromboxane A2 formation. In addition, because frequent repeated and synchronous dosing of aspirin was necessary, aspirin's potentiating effects appear to be produced by mechanism(s) unrelated to its potent, irreversible inhibition of platelet cyclooxygenase.

Selective thromboxane inhibition: a new approach to antiplatelet therapy

Antiplatelet drugs as exemplified by aspirin are used frequently to prevent stroke. Aspirin inhibits the formation of both the potent platelet aggregator, thromboxane A2 and the potent anti-aggregator, prostacyclin. Another approach to the inhibition of platelet aggregation might involve selective suppression of thromboxane formation. We report our experience in swine with UK-38,485, a drug which selectively inhibits thromboxane formation. The rationale and potential uses of UK-38,485 in the in vivo prevention of platelet aggregation and for the therapy of cerebrovascular disease are discussed.

Study of platelet activation in migraine: control by low doses of aspirin

Although platelet activation is known to occur during migraine attacks, the cause-effect relationship remains to be determined. This problem was approached by studying the possible occurrence of platelet activation in vivo in headache-free periods of subjects affected by common or classic migraine and, subsequently, by verifying the possibility of its pharmacological control through administration of a classic anti-aggregation drug such as aspirin (ASA). The plasma levels of beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4), indices of the occurrence of platelet activation in vivo, were therefore first assayed in both groups of migraine sufferers in the absence of therapy and then during the administration of aspirin (50 mg/daily). In the group of 15 patients affected by classic migraine, basal plasma levels of beta-TG and PF4 were significantly higher than control subjects. On the other hand, only beta-TG plasma levels were significantly higher in the group of 18 patients affected by common migraine. Patients suffering from classic migraine showed a high incidence of platelet activation (greater than 90%) in comparison with common migraine patients (approximately 33%). This suggests that platelet activation occurs in vivo in migrainous patients also during headache-free periods. Administration of aspirin to the patients affected by common and classic migraine caused a decrease in plasma beta-TG and PF4 concentration. Consequently, pharmacological treatment with aspirin in adequate dose may prove to be helpful in diminishing the vascular side-effects known to occur in migraine sufferers.

Does 111indium-platelet deposition predict patency in prosthetic arterial grafts?

The relationship between the rate of 111In-platelet deposition on vascular grafts and subsequent thrombosis has been examined in patients undergoing femoropopliteal by-pass. Sixty-seven patients undergoing femoropopliteal by-pass using vein, Dacron or PTFE were randomized to aspirin plus dipyridamole (ASA/DPM) or placebo. Autologous 111In-platelets were injected in the second postoperative week and Thrombogenicity Index (TI) calculated as the mean daily rise in the ratio of radioactivity graft/contralateral thigh. Graft patency was assessed to 1 year. Mean (+s.e.m.) TI at 1 week in 21 grafts that occluded within 12 months was 0.19 +/- 0.018 compared with 0.07 +/- 0.009 in the 38 that remained patient (P less than 0.001). Grafts with a TI less or greater than the median had a 90 per cent or 39 per cent cumulative 1-year patency, respectively (P less than 0.001). In the prosthetic grafts ASA/DPM reduced mean TI from 0.17 +/- 0.02 to 0.11 +/- 0.01 (P less than 0.02) and enhanced 1-year patency from 36 to 67 per cent (P less than 0.05). Following femoropopliteal by-pass TI related to subsequent graft patency. Radiolabelled platelet deposition therefore provides a guide as to how new materials or antithrombotic drugs may influence clinical graft thrombosis. Platelet inhibition reduced both graft thrombogenicity and subsequent occlusion.