Interaction of cations and chelators with the intestinal absorption of tetracycline.

The influence of certain compounds on intestinal absorption of tetracycline was tested, using two different in vivo techniques: a) Disappearence of the drug from perfused intestinal segments of the rabbit; b) Measuring urinary excretion in the rat after oral dosage. Ca2+ and Fe2+ ions both reduced the permeation rate of tetracycline by about 30%. In presence of Ca2+ and salicylate ions, leading to ion-pair formation with the antibiotic, intestinal uptake was significantly increased in comparison to experiments where only calcium was present. A more pronounced increase was observed with EDTA. Phosphate ions had different effects on the uptake of the antibiotic in both experimental techniques. Possible mechanisms are discussed.