The Effect of Ingestion of Nicotinic Acid on the Determination of Thiamine in Urine by the Thiochrome Method*

The present study was prompted by the observation that ingestion of large amounts of nicotinic acid resulted in a relatively large increase in the apparent excretion of thiamine by human subjects maintained on a constant low intake of thiamine. Although the daily excretion of thiamine had been at a fairly constant level, between 20 and 30 y for several months, after administration of 300 mg. of nicotinic acid for 2 days the daily excretion of “apparent” thiamine rapidly increased to more than 100 y, a level that might, be considered normal. It became desirable to know whether the ingestion of nicotinic acid actually stimulated the excretion of thiamine or whether a large amount of nicotinic acid or of its metabolic products in the urine so affected the determination as to give false values. It was soon found that nicotinic acid added to urine had no effect on the determination. In the thiochrome method of Hennessy and Cerecedo (1) the urine is passed through a column of permutit which retains the thiamine, and most of the material which interferes with the determination of thiamine passes into the filtrate. It, has been recognized (2, 3), however, that not, all of the material which interferes with the determination of thiamine is thus eliminated. Some of it remains on the permutit and is removed with the thiamine when the column is washed with a 25 per cent solution of potassium chloride. This solution of potassium chloride containing the thiamine is treated with sodium hydroxide and ferricyanide to