The influence of acetylsalicylic acid on platelet adhesiveness and thrombotic fistula complications in hemodialysed patients

Thromboprophylactic effect of ticlopidine in arteriovenous fistulas for haemodialysis

When constructing arteriovenous fistulas for haemodialysis in chronic renal failure patients, one of the main problems is still their clotting tendency. Ticlopidine is an effective inhibitor of platelet aggregation. In this randomized double-blind study placebo or ticlopidine 250 mg twice daily was given to chronic uremic patients up to 4 weeks after construction of an arteriovenous fistula. 42 patients were recruited and 36 completed the trial. The fistula clotted in 8 patients on placebo and in 2 patients on ticlopidine. The difference is significant. This effect was achieved without an increased frequency of side effects compared with placebo. It is concluded that ticlopidine has a function as a thromboprophylactic drug in chronic uremic patients.

Successful creation of arteriovenous fistulas in nonuremic patients with heparin and aspirin therapy

From November 1977 through June 1979, 26 of 28 nonuremic patients had forearm arteriovenous fistulas successfully created for dialysis, lymphapheresis or vascular access. To improve patency, aspirin and heparin therapy was begun the night before operation and continued postoperatively in all except one patient. No major change in coagulation parameters resulted from this treatment. Twenty-five radial artery to cephalic vein fistulas were created in 23 patients, brachial artery to basilic vein fistulas in 3 patients, and 8 mm polytetrafluoroethylene brachial artery to basilic vein loop grafts in two patients. Early fistula failures (within 11 days) required thrombectomy once in four patients and twice in another patient. A sixth patient was not given heparin or aspirin and required multiple thrombectomies before the graft was removed because of infection. One other patient refused further surgery after two unsuccessful attempts to create an arteriovenous fistula. In the remaining 26 patients, the fistulas have been successfully maintained, and in 18 patients more than 214 dialysis or lymphapheresis treatments have been performed without problems. The successful establishment of arteriovenous fistulas in nonuremic patients has been achieved by giving aspirin and low dose heparin therapy, which appears to be an integral step in maintaining patency.

Thrombosis: the relationship of hemostatic mechanisms to drug therapy

The mechanism of action and present clinical role of drugs affecting hemostasis in the therapy of spontaneous, postoperative, and posttraumatic arterial thrombosis, arterial embolism, venous thrombosis, pulmonary embolism, and intracranial aneurysm have been reviewed. Both the management of neurosurgical problems and the development of antithrombotic regimens are improving. In regard to the use of drug therapy, discussed herein, each surgeon will reach his own decision based on his findings in the individual patient, and may wisely elect in specific situations not to employ drug therapy. The comments offered in ths analysis are to be construed as suggestions not mandates, as they will undoubtedly undergo modification with time. In closing, it is appropriate to recall a famous Chinese curse: "May you live," it reads, "in a time of transition."

Potential therapeutic applications of aspirin and other cyclo-oxygenase inhibitors

1 The ubiquitous actions of the cyclo-oxygenase inhibitors are described. 2 These include the inhibitory effect on prostaglandin synthesis and the direct effect of aspirin on lymphocytes and their ability to produce lymphokines. 3 Aspirin reduces some types of platelet aggregation possibly involving inhibition of the precursors of thromboxane A2 and prostacyclin. 4 The therapeutic implications in relation to transient ischaemic attacks, coronary artery disease and reno-allograft rejection are discussed. 5 The beneficial and adverse effects on the gastro-intestinal tract are described. 6 The effects of aspirin-like drugs on the genito-urinary tract are described with particular reference to their adverse effects on labour and their therapeutic effect on dysmenorrhoea.

Influence of antiplatelet drugs on platelet-surface interactions

Platelet aggregates are important in the thromboembolic complications of prosthetic devices, and drugs that alter platelet function have shown promise in clinical trials. Results with these drugs have increased insight into the interaction of platelets with artificial materials, particularly when the clinical experience has been correlated with the results of in vitro models. In a bead column/surface contact model, the characteristic interactions of platelets with artificial surfaces resemble effects of adding thrombin ADP to platelet-rich plasma. Anti-inflammatory agents and other antiplatelet drugs inhibit these reactions. Results in an in vivo model, survival of 51 Cr-labeled platelets in sheep bearing arteriovenous shunts of test materials, correlate systems indicate that the initial events upon contact of a surface with plasma proteins persistently influence the long-term behavior of that surface toward blood. A review of clinical studies discusses the effect of antiplatelet drugs on platelet survival and also on thrombotic complications of heart valve replacement and other conditions employing prosthetic devices.

[Prophylaxis and therapy of shunt thrombosis in terminal renal insufficiency (author's transl)]

In terminal renal insufficiency thrombosis occurs almost exclusively in the arteriovenous shunt. The management of this acute, life threatening thrombosis is hardly contested. On the other hand, few results are available concerning effective thrombosis prophylaxis. In addition to the effectiveness, the pharmacokinetics of a substance and also possible bleeding complications must be taken into account. The parenteral administration of heparin and its short half life restrict it to use in thehospital. Oral anticoagulants, because they are difficult to dose, should be avoided when possible. Dextrans (Rheomacrodex) and acetylsalicylic acid (Colfarit) appear to be best suited for thrombosis prophylaxis in renal insufficiency. Dextran has the disadvantage of volume overload, and acetylsalicylic acid that of stomach intolerance. Sulfinpyrazone (Anturano) also appears to be effective, although its pharmacokinetic behaviour in renal insufficiency is still not known. Dipyridamole (Persantin), whose effectiveness for this purpose has not yet been demonstrate, should be administered even more cautiously.

Are agents affecting platelet functions clinically useful?

Notwithstanding the large number of clinical trials, most of them designed and performed according to the requirements of modern clinical pharmacology, only a few firm clinical recommendations on drugs affecting platelet function in the prevention of arterial or venous thrombosis can be made at present. There is no good evidence for the clinical effectiveness of aspirin or any other drug affecting platelet function in patients with peripheral arterial occlusion or after vascular grafting. In cerebrovascular disease there is reasonable evidence that the administration of sulfinpyrazone can significantly reduce cerebral ischemia or mortality, but similar trials performed with aspirin, dipyridamole or clofibrate failed to reveal a significant difference in favor of the experimental treatment. Patients with angina only were shown to benefit from treatment with clofibrate, but prospective trials with dipyridamole or aspirin in the primary or secondary prevention of myocardial infarction did not reveal a significant reduction in morbidity or mortality in the experimental group. Use of a combination of the latter two drugs did, however, reveal a reduction in morbidity and mortality. In patients with prosthetic heart valves, there is firm evidence that dipyridamole and sulfinpyrazone therapy can normalize decreased platelet survival, an effect which has been shown to correlate well with the incidence of thromboembolism. Provided further trials lead to confirmatory conclusions, drugs inhibiting platelet function associated or not with oral anticoagulants may constitute an ideal prophylaxis in patients with a substitute valve. There is still much uncertainty as to whether dipyridamole, given in addition to conventional treatment, benefits patients with membranous or mesangiocapillary glomerulonephritis. The same holds for drugs inhibiting platelet function after kidney or heart transplantation in man. Only scanty reports are available on the usefulness of drugs affecting platelet function in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome. Three different types of antiplatelet drugs are available for the prevention of postoperative deep vein thrombosis: dextran, oral drugs also affecting platelet function and heparin administered subcutaneously in small doses. In orthopedic surgery dextran 70 administered before and every second day after surgery was the drug showing the most convincing reduction in the incidence of phlebographically proved deep vein thrombosis. Major orthopedic surgery is precisely the type of surgery in which the effectiveness of small dose heparin is much in doubt and in which the effectiveness of aspirin and dipyridamole is still to be confirmed. In general surgery, use of a combination of 1 g aspirin and 0.225 g dipyridamole daily was shown to offer approximately the same level of protection as small doses of heparin, land these two forms of prevention seem to offer a greater degree of protection than dextran...