Tissue Disposition of 3H-actinomycin D (NSC-3053) in the Rat, Monkey, and Dog

Tissue concentration of 3H-actinomycin D have been determined in the rat, monkey, and dog after an iv dose of 0.6 mg/m2 body surface area. The drug-tissue half-life was determined for various tissues of the rat, monkey, and dog. A mean drug-tissue half-life of 47 hours was calculated for the tissues of the dog. Exceptions were the testis and brain. Significant concentrations of 3H-actinomycin D failed to accumulate in the brain. Although testis drug concentrations were lower than most other tissues evaluated, the drug-tissue half-life was significantly greater than that of other tissues. In all species studied 3H-actinomycin D was rapidly depleted from serum after iv dosage, with concomitant accumulation of drug in the tissues. 3H-actinomycin D was excreted via the biliary and urinary routes in all species studied. No metabolites of 3H-actinomycin D were detected in the bile or urine of the rat, monkey, or dog with the methods employed. When expressed on a body weight basis, body surface area doses were more than threefold greater in the rat than in the dog. However, the average ratio of concentration X time values (rat C X T/dog C X T) for 11 different tissues of the rat and dog was only 1.3. The results strongly suggest that an equivalent dose of actinomycin D, with dosage based on a body surface area basis, results in nearly equal tissue-drug exposure for most tissues in various mammalian species.