Pharmaceutical Science: Research Trends and Challenges Vol. 1

Topical ocular administration of acyclovir is limited by poor corneal penetration, rapid precorneal loss, and low ocular bioavailability. This study developed acyclovir-loaded chitosan microspheres by ionic gelation with sodium tripolyphosphate and evaluated the influence of drug concentration on their physicochemical and release characteristics. Five formulations containing 25–125 mg of acyclovir and 250 mg of chitosan were prepared. The microspheres were characterised using Fourier-transform infrared spectroscopy, differential scanning calorimetry, particle-size analysis, zeta-potential measurement, scanning electron microscopy, encapsulation efficiency, loading capacity, and in vitro release testing in phosphate buffer at pH 7.4. The formulations produced smooth, spherical, micron-sized particles ranging from 2 to 12 µm, with positive zeta potentials of +36.1 to +43.6 mV. Encapsulation efficiency ranged from 52% to 78%, whereas loading capacity ranged from 12% to 26%. Increasing acyclovir concentration was associated with reductions in particle size, zeta potential, and encapsulation efficiency, together with an increase in loading capacity. Spectroscopic and thermal findings indicated interaction between acyclovir and chitosan while retaining the crystalline character of acyclovir. The selected microsphere formulation provided sustained in vitro drug release over 24 h. Release data were consistent with first-order kinetics and a non-Fickian mechanism involving combined diffusion and matrix-related processes. These findings indicate that acyclovir-loaded chitosan microspheres have potential as a controlled ocular delivery system, although further optimisation and in vivo evaluation are required.