Drug Movement between Bovine Milk and Plasma as Affected by Milk pH

As part of a study on non-ionic diffusion of drugs into milk, salicylic acid, paminohippuric acid, sulfaeetamide, sulfamcrazine, sulfamethazine, sulfathiazole, sulfapyridine, sulfanilamide, and phenol were infused into lactating cows, to maintain constant plasma concentrations for 6 hr. The right h'ont quarter of each cow was infused with sterile bicarbonate buffer solution to establish a pit value of 8.0. Blood, milk from the normal quarters, and nfilk from the bicarbonate-treated quarters were sampled simultaneously at hourly intervals. The weak organic bases, urea, antipyrinc, creatinine, aminopyrine, quinine, and ephedrine were studied in like manner. Experimentally determined milk-to-plasma ultrafiltrate ratios agreed well with theoretical ratios for non-ionic diffusion both in the normal and in bicarbonate-treated quarters. It was concluded that the passage of these compounds into bovine milk can be explained by passive diffusion.