Transfer of drugs across the ruminal wall in goats.

The rates at which pentobarbital, salicylate, antipyrine, and quinine were transferred from the rumen of intact, conscious goats were measured. The rates at which the same drugs diffused from the blood plasma (under conditions of constant drug concentration) into the ruminal solution were also evaluated. These compounds were absorbed by simple diffusion, and the rates of transfer were a function of pH of the intraruminal solution. The diffusion of drugs from plasma into the reticulorumen allowed steady-state distributions to be established in some goats. The theoretical and observed steady-state distributions were compared. There were good correlations for pentobarbital and antipyrine, but not for salicylate and quinine. These findings confirm in vivo the general principles of drug transfer across ruminal epithelium that were derived from previous studies conducted in vitro.