Caution should also be used when Niacin is used in patients with unstable angina or in the acute phase of MI, particularly when such patients are also receiving vasoactive drugs such as nitrates, calcium channel blockers or adrenergic blocking agents. Elevated uric acid levels have occurred with Niacin therapy, therefore use with caution in patients predisposed to gout. Niacin has been associated with small but statistically significant dose-related reductions in platelet count and increases in prothrombin time. Caution should be observed when Niacin is administered concomitantly with anticoagulants; prothrombin time and platelet counts should be monitored closely in such patients. Niacin has been associated with small but statistically significant, dose-related reductions in phosphorus levels (mean of -13% with 2000 mg). So phosphorus levels should be monitored periodically in patients at risk.