The Solubility and Complexing Properties of Oxytetracycline and Tetracycline I. Interaction in Aqueous Solution**School of Pharmacy, University of Wisconsin, Madison

Oxytetracycline dihydrate and tetracycline trihydrate form soluble complexes with sodium salicylate, sodium parahydroxy benzoate, sodium saccharin, sodium p -amino benzoate, caffeine, and N-methyl pyrrolidone in aqueous solution. In all cases the tetracycline interactions were greater than those with oxytetracycline. With the exception of sodium salicylate at concentrations below 0.5 M, the solubilizing activities of these compounds are roughly in the order listed above. Logarithmic plots show a linear relationship in dilute solution and the slope values of these curves reveal that an increase in solubility of the tetracyclines is concomitant with an increase in the complexing agent dependency. The solubilization may be due, in part, to the presence of strong electronegative centers within the agents used. Two recrystallization procedures for the preparation of oxytetracycline and tetracycline hydrates are described.