Long-term safety of cilostazol in patients with peripheral artery disease: The CASTLE study (Cilostazol: A Study in Long-term Effects)

Background: Cilostazol, a phosphodiesterase III inhibitor, is indicated to treat the symptoms of intermittent claudication and increase walking distance in patients with peripheral arterial disease (PAD). At the time of approval, the United States Food and Drug Administration required an additional long-term safety study to evaluate the effect cilostazol on mortality. Methods: A total of 1899 subjects with a clinical diagnosis of PAD and symptoms of claudication were screened for participation in a randomized, double-blinded, placebo-controlled safety study of cilostazol. The intent-to-treat (ITT) population, which was the primary analysis (n = 1435), was defined as all randomized patients who received at least one dose of study medication and included patients who were followed up >30 days after discontinuation of study drug. A total of 717 patients received cilostazol and 718 received placebo. Cilostazol was administered at a primary dose of 100 mg twice daily. The dose could be reduced to 50 mg twice daily if patients experienced an adverse event that might have been drug related. Results: Long-term adherence to study medication was poor, with >60% of participants discontinuing therapy by 36 months. The mortality analysis therefore focused on deaths during the period on-treatment, defined as the period during which the study drug was taken plus a 30-day follow-up period after dosing. Total patient-years of exposure were 1046 on-treatment for cilostazol and 1090 for placebo. On-treatment, there were 18 deaths on cilostazol and 19 deaths on placebo for a hazard ratio of 0.99 (95% confidence interval [CI], 0.52-1.88). Cardiovascular deaths on-treatment occurred in 14 patients on cilostazol and 14 on placebo. In the full ITT population at 36 months, there were 101 deaths, 49 on cilostazol and 52 on placebo, with hazard ratio of 0.94 (95% CI, 0.64-1.39). Thus, most deaths occurred >30 days after study drug discontinuation. Serious bleeding events affected 18 patients taking cilostazol in the on-treatment population and 22 taking placebo. The rates of bleeding events were similar in patients who used aspirin, aspirin plus clopidogrel, or anticoagulants at anytime during the course of the study Conclusions: This long-term study demonstrated no safety signal for cilostazol on all-cause or cardiovascular mortality. The study, however, was underpowered to detect a small adverse impact of cilostazol on mortality (hazard ratio upper bound of the 95% CI was 1.88 in the on-treatment population). Serious bleeding events appeared not to be increased by cilostazol.