Absorption rates of various substances administered intramuscularly

Abstract

The rates of absorption of a variety of compounds from the tibialis anterior muscle of the rat were determined. The substances studied were aqueous solutions of isotopically labeled benzylpenicillin, hexamethonium, glucose, ouabain, urea and water. The disappearance of the radioactivity from muscle was found to be exponential with time and to be described by a single rate constant. The rates were very similar and averaged 0.159/min. The absorption rates of the various substances (molecular weights 20-585) did not appear to vary with their diffusion coefficients but were affected by vasoactive substances. The results suggest that blood flow rather than diffusion is the rate limiting step for absorption from muscle. © 1971.