Absorption and Excretion of Drugs. XXXVI. Effect of Ca²⁺ on the Absorption of Tetracycline from the Small Intestine. (1)

Abstract

Effect of Ca²⁺ on the absorption of tetracycline was examined in situ, in vitro, and in vivo. It was found that tetracycline disappeared faster from recirculation solution (a) in the presence of small amounts of Ca²⁺ at pH 6.2 and (b) in the presence of Ca²⁺ irrespective of its concentration at pH 8.0. At pH 8.0, partition ratio (isoamyl alcohol/water) of tetracycline increased in the presence of Ca²⁺, exhibiting a similar pattern as that in recirculation experiments. Excretion data of tetracycline in man, however, showed that the antibiotic was less favorably absorbed in the presence of Ca²⁺. These results suggested that tetracycline chelated with metal ions would be bound to intestinal wall and that absorption would be inhibited in the presence of Ca²⁺.