Aspirin blocks nicotinic acid-induced flushing

Nicotinic acid flushing after placebo and 975-mg oral doses of aspirin was assessed in 29 normal subjects over a range of nicotinic acid doses. Intensity of flushing was assessed by the change in malar thermal circulation index (delta MTCI). Aspirin pretreatment resulted in smaller delta MTCIs at the higher doses of nicotinic acid. At the lower doses the change in the index after pretreatments with both aspirin and placebo remained low, suggesting that very little flushing was provoked by these doses. These results are compatible with the proposed mediation by prostaglandins of the nicotinic acid-induced flush. According to the delta MCTI method, flushing is quantitatively characterized as a nonquantal, dose-response reaction of variable intensity.