Ticlopidine in China: comparative study on the effect of two dose levels on bleeding time and platelet function in healthy volunteers

Analysis of antiplatelet effect of ticlopidine in humans: modeling based on irreversible inhibition of platelet precursors in bone marrow

The relationship between plasma concentration of ticlopidine and its inhibitory effect on platelet aggregation in human was analyzed using a pharmacokinetic/pharmacodynamic (PK/PD) model. The data of plasma concentration and inhibitory effect on platelet aggregation were taken from the literature. A two-compartment open model was fitted to plasma ticlopidine concentrations. Assuming that ticlopidine acts on platelet precursors in the bone marrow, the apparent reaction rate constant of ticlopidine and platelet precursors (K), apparent transformation rate constant of platelet precursors (kr) and apparent elimination rate constant of platelets (ke) were estimated. The estimated values +/- S.D. were 1.01 +/- 1.08 ml micrograms-1 hr-1 for K, 0.265 +/- 0.259 hr-1 for kr and 0.0747 +/- 0.0112 hr-1 for ke. The antiaggregation effects of ticlopidine on platelets after administration of 100, 200, and 300 mg (bid for 8 days) were simulated using the PD parameters of K, kr, and ke. While the antiaggregation effect reached steady state within 3-4 days without dose dependency of the interval, the maximum effect increased with dose. Furthermore, changing the elimination rate constant of ticlopidine from the central compartment in the model significantly changed the duration of inhibitory effect of ticlopidine on platelet aggregation. Therefore, the reported long duration of antiplatelet effect after discontinuation of ticlopidine, which is believed to be irreversible binding to the platelet, might have been partially caused by the delayed plasma elimination after a long therapy of ticlopidine. On the other hand, the mean life-span of platelets in the blood estimated by 1/ke after administration of ticlopidine was 14 hr, far below the life-span of platelets in the blood. For a more detailed analysis of the antiplatelet effect of ticlopidine, the possible contribution of reversible binding of the drug to glycoprotein IIb/IIIa should be considered in future PK/PD models.

Ticlopidine. An updated review of its pharmacology and therapeutic use in platelet-dependent disorders

Ticlopidine inhibits platelet aggregation induced by adenosine diphosphate (ADP) and most other platelet agonists in ex vivo studies of human platelets. The drug also improves other abnormalities of platelet function seen in patients with cerebrovascular disease, peripheral arterial disease, ischaemic heart disease or other conditions involving platelet hyperaggregation. Abnormal platelet activity has been implicated in a variety of clinical conditions in which patients are at high risk of thromboembolic events, and thus the effectiveness of ticlopidine has been investigated in such patients. Since the initial review of the drug appeared in the Journal, data from several large multicentre studies have shown that ticlopidine has a substantial benefit to offer patients who have experienced transient ischaemic attacks or stroke, and in those with peripheral arterial disease or ischaemic heart disease. Ticlopidine reduces the incidence of further stroke, myocardial infarction or vascular death, and is superior to placebo and aspirin in this regard in studies of patients with recent stroke or transient ischaemic attacks, or intermittent claudication. Ticlopidine is equally effective in both men and women and also improves symptoms of claudication in patients with peripheral arterial disease, and appears to reduce anginal pain. Patients with subarachnoid haemorrhage and sickle cell disease have shown some improvement with ticlopidine administration. The drug reduces thromboembolic events and re-stenosis in patients undergoing haemodialysis and cardiac surgery, and appears to prevent the progression of nonproliferative diabetic retinopathy. Ticlopidine in large clinical trials is associated with a higher incidence of adverse effects than placebo and an overall incidence similar to aspirin. Most adverse effects do not require withdrawal of treatment. Gastrointestinal symptoms (particularly diarrhoea) are most common, occurring almost twice as frequently with ticlopidine as with aspirin. Other adverse effects associated with ticlopidine include skin rash, haemorrhagic disorders, and haematological effects; these latter effects require careful monitoring of patients during the initial weeks of therapy. In conclusion, ticlopidine is a valuable addition to the prophylactic treatments available for the management of patients with cerebrovascular disease, peripheral arterial disease or ischaemic heart disease, who present a high risk of thromboembolic events. Although tolerability may be a problem for some patients, the overall benefit conferred by the drug would appear to outweigh this potential disadvantage. Because of its antiplatelet activity, ticlopidine has a promising role in other disorders mediated by platelet dysfunction. However, the precise role of the drug in these additional therapeutic indications awaits clarification with wider clinical experience.