Abstract

Adjusting and resetting the predetermined storage temperature of O/W miconazole cream from 20-24° to be 30° to coincide with the storage temperature of the Egyptian climatic ICH/WHO zone IVA was the objective of this work. Eight sets of miconazole cream were prepared by using different proportions of the oil phase ingredients while their ratios were fixed at 30 %. The calculated HLB values of the oil phases were 9.067, 9.134, 9.2, 9.267, 9.36, 9.46, 9.566 and 9.6. These eight sets have same optimum surfactants blend proportions equal to 0.5:0.5 and same effective surfactant blend concentration equal to 7 %. Sets which have storage temperature equal to 30±2° were assessed according to the acceptance criteria of the accelerating stability testing protocol for O/W emulsions stabilized by nonionic surfactants (aqueous surfactant two-phase systems) as previously reported. Only two sets, numbered 2 and 4 with storage temperature of 30.5 and 32°, respectively met the acceptance criteria of aqueous surfactant two-phase system. The applicability and validity of the method was confirmed by measuring zeta potential and particle size distribution of original miconazole cream set, set numbers 2 and 4. Zeta potential and particle size distribution of the three sets were measured on a Zetasizer with zeta potential results equal to -20, -30.7, -41.7 mV and particle size distribution results equal to 560.8, 387.6, 386.5 nm, respectively. Particle size distribution was also measured using a transmission electron microscope with results equal to 84.875, 49.168 and 46.05 nm, respectively. These results indicated that zeta potential defined the emulsion stability accurately and precisely whereas particle size distribution measurement gave unreliable and indefinite results. Zeta potential results revealed that the increase in the storage temperature of emulsion to 30° is accompanied by an increase in its stability. Increasing temperature beyond 30 is possible and would result in subsequent increase in stability due to the presence of liquid crystalline phase below 35°, which contributes significantly to emulsion stability while the destructive effect of the temperature starts at 35°. Unreliable and indefinite results of particle size measurement proved that the droplet diameter and droplet size measurement reported in many reports is more convenient. This work described a theory to determine the storage temperature of materials, pharmaceuticals, foods and cosmetics obeying non-Newtonian plastic flow.