Hepatic toxicity of unmodified and time-release preparations of niacin.

Niacin (nicotinic acid) is used frequently in the treatment of hypercholesteremia. It is available in both unmodified and time-release preparations. The latter were developed in attempts to minimize the skin-flushing reaction that affects virtually all users and may limit acceptance. Adverse effects on the liver from both unmodified and time-release preparations have been recognized for many years. We reviewed the literature on the hepatic toxicity of both types of niacin preparations. Adverse reactions in six patients resulted from the exclusive use of unmodified niacin and in two patients from the exclusive use of time-release preparations. In 10 additional patients, adverse reactions developed after an abrupt change from unmodified to time-release preparations. Many of these patients were ingesting time-release niacin at doses well above the usual therapeutic doses currently recommended. Signs of liver toxicity developed in less than 7 days in four of these 10 patients. In doses that achieve equivalent reductions in serum lipids, hepatic toxicity occurred more frequently with time-release preparations than with unmodified preparations. An awareness of toxicity associated with ingestion of high doses of time-release niacin preparations is important because of their widespread availability and the potential for self-prescribed, unmonitored use.