The effect of some additives on the adsorption of tetracycline hydrochloride on magnesium trisilicate and milk.

The effect of various additives on the adsorption of tetracycline hydrochloride on magnesium trisilicate or milk was investigated. Adsorption-elution, dialysis and sedimentation volume measurements were used in the present investigation. Citric acid was found to exert the highest adsorption suppressing effect of the antibiotic on both antacids. The nonionic surfactants, polyoxyethylene-23-lauryl ether (Brij 35) and polysorbate 80, had an intermediate action, while polyethylene glycol 6000 (PEG-6000), polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (CMC) and urea had only a slight effect. On the other hand, the effect of sodium benzoate and sodium salicylate varied with concentration. Results of the elution study showed that the efficiency of the additives, as eluting agents, was more or less parallel with their influence on adsorption. The presence of citrate or Brij 35, having the highest adsorption-suppressing effect, was found to have a negligible effect on the chemical stability or microbiological activity of tetracycline. Conclusions were made that the incorporation of some of these additives may possibly reduce tetracycline-antacids interactions and consequently improve the antibiotic availability when co-administered with antacids.