Further Studies of the Absorption, Distribution, and Elimination of Thiouracil1

Abstract

Thiouracil was very rapidly absorbed from the gastrointestinal tract. However, approx. 15% was destroyed by the contents of the gastro-intestinal tract. The proportion of the drug excreted in the urine varied in accordance with the size and frequency of dosage, but approx. one-third of the quantity ingested was eliminated by the kidneys. No thiouracil was found in the stools. It was assumed that approx. 50% was broken down by the body tissues and fluids. Each of a large number of tissues tested possessed the capacity to break down thiouracil. Sulfur balance studies following the adm. of thiouracil revealed an increased excretion of neutral sulfur, a decrease in inorganic sulfur and usually a decrease in ethereal sulfur. The thiouracil partially accounted for the increased excretion of neutral sulfur. The remainder was not accounted for by cysteine, cystine, thiourea, thiocyanate, thiosulphate, urochrome, or melanin. Frequent estimations of the conc. of thiouracil in the blood and urine throughout 24-hr. intervals showed a distinct lability in each of these fluids. Frequent small doses maintained greater constancy in the blood and urine levels than did equivalent daily amts. administered less frequently.