Solid State Adsorption of Antibiotics onto Sorbitol

Abstract

The ability of two types of sorbitol, instant and crystalline, to hold antibiotics permanently after mixing has been assessed by an air sieving technique. Sorbitol instant was found to have a greater adsorption capacity and binding strength than crystalline sorbitol. The six antibiotics studied were found to fall roughly into two groups of different adsorption capacities: (1) pivampicillin, cephalexin monohydrate and erythromycin ethylsuccinate, and (2) ampicillin trihydrate, amoxycillin trihydrate and cloxacillin sodium. The former have slightly higher levels of adsorption than the latter. A negative linear relationship was found between the amount of antibiotic adsorbed onto dry sorbitol and that originally added to sorbitol. When adsorption is expressed as the weight of drug adsorbed per unit weight of sorbitol, an 'apparent' Langmuir isotherm results. This suggests that there are a number of adsorption sites available for holding drug particles, these sites being different for the different antibiotics.