A Single-center, Randomized, Double-blind, Placebo-controlled Study of the Efficacy and Safety of Allopurinol in Improving Ischemic Symptoms in Patients With Refractory Angina.

One of the most common clinical presentations associated with coronary artery disease (CAD) is stable angina, which can be translated clinically into chest discomfort (or equivalent) evoked by different levels of physical activity depending on the extent of the disease. In the United States, it is estimated that 16.5 million individuals over 20 years of age have chronic ischemic heart disease, of which 3.4 million live with the diagnosis of angina pectoris. Refractory angina is a clinical condition characterized by the presence of debilitating symptoms secondary to CAD lasting more than three months in which the symptoms are attributed to objectively documented ischemia and not controlled with the combination of conventional antianginal agents and myocardial revascularization procedures. The estimated annual incidence of patients with refractory angina is between 50,000 and 200,000 new cases in the United States.

Allopurinol, a methylxanthine oxidase inhibitor, is widely used in the treatment of gout and asymptomatic hyperuricemia. The therapeutic potential of allopurinol in patients with cardiovascular disease has been the subject of increasing interest. In patients with CAD, the first study tested the role of allopurinol in improving exercise tolerance in 65 patients with stable angina documented by angiography and positive stress test for myocardial ischemia. After only six weeks of treatment, patients who received allopurinol showed a statistically significant increase in ergometry parameters, including time for ST-segment depression, total exercise time, and time until the onset of angina. There were no reports of adverse events. Considerable decrease in inflammatory markers and oxidative stress indicators has been demonstrated in patients with acute myocardial infarction receiving allopurinol versus placebo with a significant reduction in the risk of cardiovascular events in 2 years (10% vs. 30%, respectively). Therefore, the investigators will test the hypothesis that the use of allopurinol increases exercise tolerance and reduces angina attacks compared to placebo after 16 weeks of follow-up in patients with refractory angina.

Patients will be randomly selected to receive a placebo or allopurinol (600mg od) for 16 weeks. At baseline and after 16 weeks of treatment, exercise tolerance will be assessed through the cardiopulmonary exercising test, and myocardial ischemia will be determined using an exercise echocardiogram protocol. Biomarkers of oxidative stress will be measured in the blood and urine; endothelial-dependent vasodilation will be assessed using the reactive hyperemia protocol at the brachial artery.

For the sample size calculation, the investigators chose the primary outcome as "total exercise time (TTE) after intervention" based on the study by Noman et al. (Lancet 2010;375:2161-7). Thus, assuming that μ1 (allopurinol) = 396sec, μ2 (placebo) = 319sec and σ = 63sec, the investigators concluded that to be able to detect a difference between groups with 95% confidence (1-alfa) and 90% power (1-beta), 17 patients are needed in each study group. If the investigators consider a screen failure rate at 20%, a total of 40 patients will be needed, randomized 1:1.