High-performance liquid chromatographic determination of the stability of sisomicin in hydrophilic petrolatum ointment.

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Abstract
To investigate its suitability for topical application, the stability of sisomicin [an antibacterial agent] 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 PO43- buffer. An appropriate retention behavior of the antibiotic was obtained on a .mu.Bondapak-C18 column with a mobile phase of 2.0% (wt/vol) Na2SO4-0.005 M sodium 1-pentanesulfate (detection at 214 nm). The degradation of sisomicin followed 1st-order kinetics with regard to the remaining antibiotic in aqueous solution: the apparent 1st-order rate constants were 2.63 .times. 10-3/day at 5.degree. C and 1.70 .times. 10-2 at 25.degree. C. When incorporated in hydrophilic petrolatum, the antibiotic was 5-7 times more stable than in an aqueous medium. This was due to the reduction of its surface oxidation. Accordingly the ointment is therapeutically effective for at least 3 mo. when preserved under shielding from light at 5.degree. C.

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