Amphotericin B topical microemulsion: formulation, characterization and evaluation

The present studies were designed to develop a microemulsion (ME) formulation of Amphotericin B (Amp B) for the treatment of invasive fungal infections. The oil phase was selected on the basis of drug solubility whereas the surfactant and co-surfactant were screened and selected on the basis of their oil solubilizing capacity as well as their efficiency to form ME. Pseudo-ternary phase diagrams were constructed and on the basis of ME existence ranges various formulations of Amp B were developed. The influence of surfactant and co-surfactant mass ratio (Smix) on the ME formation and permeation of ME through excised rat skin was studied. The optimized formulation (ME 7) consisting of 0.1% (w/w) Amp B, 5% (w/w) Isopropyl Myristate and 35% (w/w) Smix (3:1, Tween 80 and Propylene glycol), has shown a globule size of 84.20 ± 2.13 nm, a polydispersity index of 0.164 ± 0.031, pH 7.36 ± 0.02 and conductance of 229.3 ± 1.95 μS. ME 7 exhibited 2-fold higher drug permeation as compared to plain drug solution. Besides this, the formulation was also evaluated for drug content, stability, skin retention, skin sensitivity and anti-fungal activity. In vitro anti-fungal activity in Trichophyton rubrum fungal species have shown that ME7 has higher zone of inhibition and the formulation was found stable at 2-8°C and at room temperature (25 ± 2°C) for the period of three months. The results indicate that, the investigated ME may be used as a promising alternative for Amp B therapy.