Abstract

A colorimetric procedure is described for the determination of Dilantin by nitration of the phenyl group, reduction to an aromatic amine, followed by diazotization and coupling with the Bratton-Marshall reagent. A double extraction procedure is used to separate Dilantin from biological specimens, and a 2-plate countercurrent extraction procedure is described for separating Dilantin from phenobarbital prior to colorimetric analysis.

The colorimetric procedure has been applied to the determination of Dilantin concentrations in blood plasma and tissues following the administration of Dilantin. In the rat, highest concentrations were found in the liver and fat, followed in order of decreasing concentration by the heart, spleen, kidney, lung and skeletal muscle. Red blood cells were found to contain Dilantin in approximately the same concentration as plasma. Maximum blood levels were found in the rat in 6 to 8 hours after oral dosage (100 mgm./kgm.). A dog receiving 25 mgm./kgm. showed maximum blood levels in about 4 hours, with return to zero levels after 24 hours. Human subjects receiving a single 400 mgm. oral dose of sodium Dilantin showed maximum plasma levels of 2 to 5 microgm./ml. in about 8 hours, with a slow drop occurring thereafter at the rate of 50 per cent per 18 to 24 hours. Acid Dilantin crystals were found to be more slowly absorbed over a longer time period, resulting in lower but more prolonged blood levels. Epileptic patients receiving daily doses of Dilantin and phenobarbital over a period of years showed plasma levels of 0.9 to 10.5 microgm. per ml. These levels were fairly constant for each individual, but varied considerably between different individuals.

Peroral administration of Dilantin to rats resulted in about 10 per cent of the dose being excreted in the feces. Only small amounts of Dilantin (∼1 per cent) were recovered in the urine by the assay procedure, and it is not certain that this represents unchanged Dilantin. Similar results were obtained on urinary excretion following parenteral administration of Dilantin. Small amounts of Dilantin were found in the bile of rats, and some degree of absorption was found in all parts of the gastro-intestinal tract.

Unchanged Dilantin was recovered from rat liver and human plasma, and identified by comparison with a known sample of Dilantin through its Craig countercurrent distribution characteristics. Dilantin was also recovered from dog liver, and identified by comparison of its infra-red absorption spectrum with an authentic sample of Dilantin.