Abstract
For the purpose of investigating of its suitability for topical application, the stability of sisomicin incorporated in hydrophilic petrolatum was investigated under various storage conditions by high-performance liquid chromatography. Sisomicin was extracted from the oleaginous vehicle, which was kept in a liquid state by adding liquid paraffin, using pH 6.5 phosphate buffer. An appropriate retention behavior of the antibiotic is obtained on a μBondapak-C18 column with a mobile phase of 2.0% (w/v) sodium sulfate-0.005 M sodium 1-pentanesulfate (detection at 214 nm). The degradation of sisomicin follows first-order kinetics with regard to the remaining antibiotic in aqueous solution : the apparent first-order rate constants are 2.63×10-3 d-1 at 5°C and 1.70×10-2 d-1 at 25°C. When incorporated in hydrophilic petrolatum, the antibiotic is 5 to 7 times more stable than in an aqueous medium. This is due to the reduction of its surface oxidation. Accordingly, the ointment is therapeutically effective for at least 3 months when preserved under shielding from light at 5°C.
