Metabolic response of humans to ingestion of nicotinic acid and nicotinamide.

The identification of nicotinamide-N1-oxide as a metabolite in the urine of a schizophrenic patient prompted a study of the relative metabolism of nicotinic acid and nicotinamide in mental patients and healthy volunteers. Metabolites quantified included N1-methyl-2-pyridone-5-carboxamide, N1-methyl-4-pyridone-3-carboxamide, N1-methylnicotinamide, nicotinuric acid, and nicotinamide-N1-oxide. More of most of these metabolites evidently was excreted after nicotinamide ingestion than after nicotinic acid. At the highest doses (3000 mg/day), the relative proportions of these metabolites in the urine were changed. There were only slight difference between healthy individuals and mental patients in the quantities of metabolites excreted, and no statistically significant trends were noted.