THE DISTRIBUTION OF TETRACYCLINES IN TISSUES OF DOGS AFTER REPEATED ORAL ADMINISTRATION

¹ Medical Research Laboratories, Chas. Pfizer & Co., Inc., Groton, Connecticut

The concentrations of five tetracycines—oxytetracycinc, OTC (Terramycin); 6-methyleneoxy- tetracycline, MOTC (methacycline, Rondomycin); 6-demethylchlortetracycline, DMCT (Declomycin); -6-deoxyoxytetracycine, DOOTC (doxycycline); and 6-demethyl-6-deoxytetracycline, DMDOTC—in canine tissues were determined after repeated oral administration of these drugs. It was found that the distribution of the antibiotics between tissue depots and interstitial fluid correlates well with the partition coefficients in chloroform and water, a measure of the lipid solubilities of the compounds. Although two tetracyclines may be similarly distributed in accordance with their like lipid solubilities, they will show vastly different total serum concentrations if they differ in serum protein binding. The correlation of drug serum concentrations achieved with tetracyclines in humans and dogs in discussed.