<P> Nicotinamide may be obtained from the diet where it is present primarily as NAD+ and NADP+ . These are hydrolysed in the intestine and the resulting nicotinamide is absorbed either as such, or following its hydrolysis to nicotinic acid . Nicotinamide is present in nature in only small amounts, however it is the main form of vitamin B3 in plasma . In unprepared foods, niacin is present mainly in the form of the cellular pyridine nucleotides NAD and NADP . Enzymatic hydrolysis of the co-enzymes can occur during the course of food preparation . Boiling releases most of the total niacin present in sweet corn as nicotinamide (up to 55 mg / kg). </P> <P> Nicotinamide may be toxic to the liver at doses exceeding 3 g / day for adults . </P> <P> A prescription extended release niacin, Niaspan, has a film coating that delays release of the niacin, resulting in an absorption over a period of 8--12 hours . The extended release formulations generally reduce vasodilation and flushing side effects, but increase the risk of hepatotoxicity compared to the immediate release forms . </P> <P> A formulation of laropiprant (Merck & Co., Inc .) and niacin had previously been approved for use in Europe and marketed as Tredaptive . Laropiprant is a prostaglandin D2 binding drug shown to reduce vasodilatation and flushing up to 73% . The HPS2 - THRIVE study, a study sponsored by Merck, showed no additional efficacy of Tredaptive in lowering cholesterol when used together with other statin drugs, but did show an increase in other side effects . The study resulted in the complete withdrawal of Tredaptive from the international market . </P>

Nicotinic acid pharmacological effects and mechanisms of action