Abstract
Gastrointestinal absorption of the free base and the hydrochloride of chlortetracycline (CTC) was studied in rats and human subjects. Following oral administration, the free base produced higher CTC levels in the body fluids than the hydrochloride. The difference between the bioavailability of the free base and that of the hydrochloride was due to the difference in the solubility characteristics at the gastric pH. Similar investigations were carried out with demethylchlortetracycline (DMCT) and methacycline (MOTC). The results indicated that plasma level after oral administration of MOTC base to rats was slightly higher than that of the hydrochloride and plasma levels of DMCT base and the hydrochloride were essentially identical. In the study comparing the cumulative amounts of MOTC base and the hydrochloride after oral administration to human subjects, the free base gave greater cumulative amounts than the hydrochloride in two of the three subjects.
