Abstract
Niosomes are increasingly explored for enhancing drug penetration and retention in ocular tissues for both posterior and anterior eye delivery. They have been employed in encapsulating both hydrophilic and hydrophobic drugs, but their use is still plagued with challenges of stability and poor entrapment efficiency particularly with hydrophilic drugs. As a result, focus is on understanding the parameters that affect their stability and their optimization for improved results. Pilocarpine hydrochloride (HCl), a hydrophilic drug is used in the management of intraocular pressure in glaucoma. We aimed at optimizing pilocarpine HCl niosomes and evaluating the effect of sonication on its stability-indicating properties such as particle size, polydispersity index (PDI), zeta potential and entrapment efficiency. Pilocarpine niosomes were prepared by ether injection method. Composition concentrations were varied and the effects of these variations on niosomal properties were evaluated. The effects of sonication on niosomes were determined by sonicating optimized drug-loaded formulations for 30 min and 60 min. Tween 60 was confirmed to be more suitable over Span 60 for encapsulating hydrophilic drugs, resulting in the highest entrapment efficiency (EE) and better polydispersity and particle size indices. Optimum sonication duration as a process variable was determined to be 30 min which increased EE from 24.5% to 42% and zeta potential from (−)14.39 ± 8.55 mV to (−)18.92 ± 7.53 mV. In addition to selecting the appropriate surfactants and varying product composition concentrations, optimizing sonication parameters can be used to fine-tune niosomal properties to those most desirable for extended eye retainment and maintenance of long term stability.
Highlights
Optimum drug delivery to the eye is especially difficult as the eye possesses intrinsic anatomical and physiological properties that pose barriers
Pilocarpine hydrochloride is used for managing intraocular pressure (IOP) in the treatment of glaucoma
Vesicles were unilamellar as is characteristic of niosomes formed by ether injection method
Summary
Optimum drug delivery to the eye is especially difficult as the eye possesses intrinsic anatomical and physiological properties that pose barriers. It is a miotic drug that acts as a muscarinic agonist, causing ciliary muscle contraction that opens up the trabecular meshwork which allows aqueous humour drainage and a resultant reduction in IOP (Jain and Verma 2020) It is hydrophilic in nature and its use as a conventional eye drop is faced with the challenges highlighted prior, leading to short retention times, low bioavailability and reduced efficacy (Keipert et al 1996). It is currently available in other dosage forms as oral tablets, ocular inserts, which are associated with limitations such as poor bioavailability and invasiveness due to inserts
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