Stabiliteit minoxidillotion

Physical and chemical stability of 5 per cent w/v minoxidil lotion

By ANDREW McKENDRICK, DMS, MRPharmS and PETER GALLAGHER, BSc, MRSC

OBJECTIVE • To investigate the physical and chemical stability of 5 per cent w/v minoxidil lotion in a base

containing industrial methylated spirit, propylene glycol and water.

DESIGN • Physical and chemical assessment of stored reference samples and comparison with recently

made batches, Using a high performance liquid chromatographic method, with degradation testing of

sample and standard solutions to confirm that the method of analysis was stability indicating. Thirty-six reference

samples of 5 per cent w/v minoxidil lotion were stored in 1OOml ribbed amber bottles at room temperature

for up to one year.

OUTCOME MEASURES • Changes in appearance, odour, volume of fill, density, and percentage label strength.

RESULTS • No major changes in minoxidil concentration were seen on storage, the mean variation in initial

minoxidil concentration being ±2. 7 per cent. Odour, density and volume of fill were unchanged over the storage

period. The product showed a slight yellow discoloration, with powdery deposits developing around the bottle rims after six to eight months' storage at 25C; crystallisation was observed in five samples, but was enhanced after storage at 6C for 48

hours. The degradation study demonstrated that the HPLC method was stability indicating. In solutions degraded by oxidation by addition of hydrogen peroxide, an intense yellow colour was observed in oxidised samples and on the chromatograms;

degradation peaks were resolved from active peak and no interference was noted.

CONCLUSION • Minoxidil lotion 5 per cent w/v can be stored for six months with minimal degradation,

and the HPLC method used satisfactorily resolves degradation products.