A WAY TO IMPROVE THE STABILITY OF AMPHOTERICIN B MICROEMULSIONS USING FULL FACTORIAL DESIGN APPROACH
Factorial design; Amphotericin B; Microemulsion; Oxidation
PURPOSE: The aim of this work was to improve the stability of the amphotericin B (AmB) inside the microemulsion systems by optimizing the type and the concentration of antioxidants. A 22 full factorial central composite design was developed in order to improve the oxidative stability of the drug and the lipid-based formulation. METHODS: Rancimat and DLS were used to evaluate the oxidation induction time and the droplet size during the experimental design. The optimized formulation and controls were submitted to an accelerated stability study by storing the microemulsions with and without AmB and Ethylenediamine Tetraacetic Acid (EDTA) at different temperatures. Droplet size, zeta potential, pH and drug content, performed by spectrophotometry, were the evaluation criteria. RESULTS: Among the antioxidants used on the design of experiment study and the data extrapolation, Sodium Metabisulfite (META) did not reduce the oxidation of the formulation in any concentration. The optimized formulation with 0.02 g.mL-1 EDTA was the most effective product to avoid oxidation. The addition of EDTA did not change significantly the droplet size of the ME. However, EDTA was able to provide better antioxidant action to a ME without AmB. The accelerated stability study showed that the MEs remained physico-chemically stable for over 60 days at 4 °C and 25 °C. However, a non-temperature-dependent loss of AmB was observed to be slightly reduced in the presence of EDTA. CONCLUSIONS: The factorial design of experiment allowed to determine an ideal concentration of EDTA able to increase the stability of the ME formulation. This was demonstrated by the increase in oxidation induction time of the blank formulation and by the reduction of the AmB loss.