The adsorption of selected antibiotics by Kaolin

In this investigation, the in vitro adsorption of tetracycline hydrochloride, neomycin sulfate, lincomycin hydrochloride, chloramphenicol, and ampicillin trihydrate by kaolin were studied. Adsorption studies were carried out at 37.0°C. in water and in pH 1.2, 3.0, and 5.0 solutions. The adsorption isotherms for tetracycline hydrochloride, neomycin sulfate, and lincomycin hydrochloride in aqueous solution were of the Langmuir type, with the following exceptions. (a) A Ereundlich adsorption isotherm was obtained for tetracycline hydrochloride in pH 1.2 solutions. (b) An S type adsorption isotherm, (according to the classification of isotherms by Giles and his coworkers (1960) was obtained for lincomycin hydrochloride in pH 1.2 solutions. In general, adsorption varied with the pH of the solutions. Chloramphenicol and ampicillin trihydrate are not adsorbed by kaolin. Desorption studied for the adsorbed antibiotics were carried out in. water. The results indicated that the adsorption of tetracycline hydrochloride by kaolin is a reversible process, the adsorption of neomycin sulfate by kaolin is an irreversible process, and the adsorption of lincomycin hydrochloride is a partially reversible process. On the basis of data obtained, it was found that 47.21% of 250 mg. tetracycline hydrochloride dose and, 57.98% neomycin base (220.5 mg.) would be adsorbed by six gm. of kaolin. On the basis of a 500 mg. dose of 1incornycin hydrochloride/ 11.44% would be.expected to be adsorbed by.six gm. of kaolin. This value increases to 33.94% if 17.76 gm. of kaolin are' administered to the patient. If the above two values are compared to the in vivo data reported by Wagner (1966), it becomes evident that the decrease in plasma levels (by about 90%) is much greater than that which would be predicted on the basis of in vitro adsorption studies. However, Wagner (1966) studied a commercial preparation (Kaopectate) and it-may be that other ingredients contribute to the dramatic decrease in blood levels. Therefore, in vitro data cannot be.disregarded but, at the same time > should not be extrapolated to in vivo drug effects. The final proof must come from carefully control studies in man.Pharmaceutical Sciences, Faculty ofGraduat