Soluplus micelles for acyclovir ocular delivery: Formulation and cornea and sclera permeability

Abstract

Nearly 20% of people affected by the herpes simplex virus (HSV) suffer from vision problems. The virus can infect all layers of the cornea or cause inflammatory diseases of the sclera. The aim of this work was to test whether encapsulation of acyclovir in Soluplus or Solutol polymeric micelles increases its solubility, corneal permeability and sclera penetration. The aqueous solubility of acyclovir is known to be low, and therefore approaches that increase both its solubility and ability to penetrate through the eye may favor the efficacy of the treatments. Copolymer dispersions (covering wide range of concentrations) were prepared in water and PBS 7.4 and characterized regarding size and Z-potential (close to zero). Solutol micelles increased their size when the drug was incorporated (135 vs. 19 nm), while Soluplus micelles showed little difference (137 nm). Only Soluplus micelles significantly enhanced acyclovir solubility and withstood dilution stability tests. Soluplus (12–20%) formulations showed a progressive increase in viscoelasticity as temperature rose, which may allow for easy dropping onto the eye and subsequent retention in the gel form. Drug permeability through bovine cornea and sclera was investigated in detail. Although similar permeability coefficients were recorded for the drug when applied as the free drug in solution or formulated in Soluplus micelles, the micelle formulation significantly shortened the permeation lag time through the cornea. Moreover, Soluplus micelles were advantageous compared to the drug solution in terms of greater amount of acyclovir accumulated in both cornea and sclera, and higher steady state flux. If compared with cornea, the amounts of drug permeated through the sclera were approx. 10 times greater, which opens the possibility of drug delivery to the posterior eye segment.