Absorption and excretion of riboflavin in the rat: an unusual example of nonlinear pharmacokinetics

Riboflavin requirement of chicks fed purified amino acid and conventional corn-soybean meal diets

Three experiments were conducted to determine the riboflavin requirement for maximal growth of young chicks. Graded levels of crystalline riboflavin were added to either riboflavin-free, purified amino acid diets or corn-soybean meal diets. Chick growth responses were obtained upon adding riboflavin to both diets. Chicks fed the purified diet required 1.8 mg of riboflavin per kg of diet, but those fed the corn-soybean meal diet required 2.63 mg of riboflavin per kg of diet. Retarded growth and leg paralysis, rather than curled-toe paralysis, were the predominant signs of riboflavin deficiency. Calculations suggested that riboflavin bioavailability in the corn-soybean meal diet was 59.1%.

Validity of oral bioavailability estimates of phenolsulfonphthalein based on total urinary excretion from rats

Urinary recovery of phenolsulfonphthalein from rats were determined after intracardial (0.075 mg) and oral (1.5 mg) doses. Although trace quantities of conjugated metabolites could be identified by TLC, the levels present did not introduce significant error into estimates of total phenolsulfonphthalein excretion if samples were assayed directly by colorimetric methods for only unchanged dye. The absolute availability of phenolsulfonphthalein based on urinary recovery under the present experimental conditions was estimated at 10.6%.

GI drug absorption in rats exposed to cobalt-60 gamma-radiation I: Extent of absorption

The extent of absorption of sulfanilamide, bretylium tosylate, sulfisoxazole acetyl, and riboflavin was determined in rats exposed to 850 rad of cobalt-60 gamma-radiation of sham irradiated. The drug were administered orally at 1 or 5 days postirradiation, and the amount of drug excreted in the urine was used as the measure of absorption. Following intravenous drug administration, there was no difference between irradiated and control animals in the amount of drug excreted in the urine. At 1 day postirradiation, the absorption of sulfanilamide and bretylium was not affected by radiation; the absorption of sulfisoxazole acetyl and riboflavin was increased. The fraction of sulfanilamide excreted in the urine as N4-conjugate was increased at 1 day postirradiation. At 5 days postirradiation, there was no detectable difference between irradiated and control animals in the extent of drug absorption. The effects of radiation on the extent of absorption of orally administered drugs were most pronounced immediately following irradiation. Irradiation apparently does not affect the absorption of drugs that are normally well absorbed or poorly absorbed due to slow transport across the GI mucosa. Following irradiation, there may be an increase in the extent of absorption of drugs that are poorly absorbed due to low aqueous solubility or that are absorbed by a saturable transport mechanism.