The stability and blanching efficacy of betamethasone‐17‐valerate in emulsifying ointment

Abstract

The bio‐availability of betamethasotie‐17‐valerate (Betnovate® ointment) in emulsifying ointment (1 in 4 dilution) was investigated in ten subjects using a single‐application vasoconstrictor assay; the blanching induced was measured using a skin reflectance spectrophotometer. The vasoconstrictor activity of the diluted preparations decreased with age. There was no significant difference between the vasoconstrictor activity of freshly made Betnovate 1 in 4 in emulsifying ointment and undiluted Betnovate® ointment, and between 3–4 week old diluted Betnovate and emulsifying ointment base. Blanching induced by freshly prepared 4, 8 and 16‐fold dilutions was not significantly different but a large reduction in blanching occurred on diluting 32‐fold with emulsifying ointment. The degradation of betamethasone‐17‐valerate in emulsifying ointment was quantified by high performance liquid chromatography. More than 60% of the betamethasone‐17‐valerate underwent degradation within 6 h. There was a simultaneous increase in the concentration of betamethasone‐21 ‐valerate which peaked within 2 days and was followed by a slow degradation (half‐life 8 days) to betamethasone free alcohol. Copyright © 1982, Wiley Blackwell. All rights reserved