Synthesis and evaluation of mucoadhesive acryloyl-quaternized PDMAEMA nanogels for ocular drug delivery.

Poly((2-dimethylamino)ethyl methacrylate) (PDMAEMA) nanogels were synthesized via surfactant-free free-radical polymerization technique in aqueous conditions utilizing N,N'-methylene-bis-acrylamide (MBA) as a crosslinking agent. The PDMAEMA nanogels were subsequently quaternized with acryloyl chloride in order to yield mucoadhesive materials which incorporate two mucoadhesive concepts; electrostatic interactions and covalent bond forming acrylate groups. The native PDMAEMA nanogels were found to exhibit good mucoadhesive properties on ex vivo bovine conjunctival tissues, which was found to increase proportionally with the degree of quaternization. With a view to determine the ocular drug delivery capabilities of the materials, both quaternized and native nanogels were loaded with pilocarpine hydrochloride via an absorption method, and their in vitro release profiles were analysed. The nanogels were found to exhibit a high loading capacity (>20% of total weight) and a sustained release over 6h.

Characterization of pilocarpine-loaded chitosan/Carbopol nanoparticles.

Patients using ophthalmic drops are faced with frequent dosing schedules and difficult drop instillation. Therefore, a long-lasting pilocarpine-loaded chitosan (CS)/Carbopol nanoparticle ophthalmic formulation was developed. The physicochemical properties of the prepared nanoparticles were investigated using dynamic light scattering, zeta-potential, transmission electron microscopy, Fourier transform infrared ray spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The sustained-release effects of pilocarpine-loaded nanoparticles were evaluated using in-vitro release and in-vivo miotic tests, and compared with pilocarpine in solution, gel and liposomes. We found that the prepared nanoparticles were about 294 nm in size. DSC and FT-IR studies suggested that an electrostatic interaction between CS and Carbopol contributes at least in part to the stabilization of pilocarpine/CS/Carbopol nanoparticles. When compared with pilocarpine in solution, gel or liposomes, the best slow-release profile of pilocarpine from the prepared nanoparticles occurred in a dissolution test. In the in-vivo miotic study, pilocarpine-loaded CS/Carbopol nanoparticles showed the most significant long-lasting decrease in the pupil diameter of rabbits. The advantages of CS and Carbopol are good biocompatibility, biodegradability and low toxicity. CS is also a mucoadhesive polymer. Thus, pilocarpine/CS/Carbopol nanoparticles may provide an excellent potential alternative ophthalmic sustained-release formulation of pilocarpine for clinical use. CS/Carbopol nanoparticles may also be useful for a variety of other therapeutic delivery systems.

Nanoparticle cross-linked collagen shields for sustained delivery of pilocarpine hydrochloride.

Glaucoma is a common progressive eye disorder which remains the second leading cause of blindness worldwide. Current therapy involves frequent administration of eye drops which often results in poor patient adherence and therapeutic outcomes. The aim of this study was to overcome these limitations by developing a novel nanoparticle cross-linked collagen shield for sustained delivery of pilocarpine hydrochloride (PHCl). Three metal oxide nanoparticles (NPs); titanium dioxide (TiO2), zinc oxide (ZnO) and polyvinylpyrrolidone (PVP) capped zinc oxide (ZnO/PVP), were evaluated for their cytotoxicity as well as shield transparency before selecting ZnO/PVP NPs as the ideal candidate. Cross-linked collagen shields were then characterized for their mechanical strength, swelling capacity and bioadhesive properties, with ZnO/PVP NP cross-linked shields showing the most favorable characteristics compared to plain films. The shield with the best properties was then loaded with PHCl and in vitro release of zinc ions as well as PHCl was measured without and with further cross-linking by ultraviolet irradiation. The concentration of zinc ions released was well below the IC50 rendering them safe for ocular use. Moreover, collagen shields cross-linked with ZnO/PVP NPs released PHCl over a period of 14 days offering a promising sustained release treatment option for glaucoma.

In vitro evaluation of pluronic F127-based controlled-release ocular delivery systems for pilocarpine.

The overall objective of this study was to develop pluronic F127 (PF127)-containing formulations of pilocarpine hydrochloride (PHCL) suitable for controlled-release ocular delivery of PHCL. Various aqueous formulations were evaluated containing 1% w/v PHCL and 25% w/v PF127 alone or with one of the following additives present: poly(ethylene glycol) 4600 (PEG), poly(vinylpyrrolidone) 10,000 (PVP), poly(vinyl alcohol) 10,000 (PVA), methylcellulose 15 cP (MC), and hydroxypropyl methylcellulose 80-120 cP (HPMC). The in vitro dissolution of the PF127 formulations and the pilocarpine release profiles from them were obtained simultaneously at 34 degrees C and room temperature using a membraneless in vitro model. It was observed that the PEG- and PVP-containing PF127 formulations of PHCL dissolved the quickest and released the drug at a significantly faster rate than the control PF127 formulation, which had no additive present. The PF127 formulations of PHCL containing MC or HPMC exhibited the slowest dissolution rates and released the drug the slowest. The same rank order was observed at each temperature for the dissolution and PHCL release profiles of each formulation. On the basis of the in vitro results, the PF127 formulations of PHCL containing MC or HPMC as an additive showed potential for use as controlled-release ocular delivery systems for PHCL.

In situ gelling xyloglucan formulations for sustained release ocular delivery of pilocarpine hydrochloride.

Thermoreversible gels formed in situ by aqueous solutions of an enzyme-degraded xyloglucan polysaccharide were evaluated as sustained release vehicles for the ocular delivery of pilocarpine hydrochloride. In vitro release of pilocarpine from gels formed by warming xyloglucan sols (1.0, 1.5 and 2.0% w/w) to 34 degrees C followed root-time kinetics over a period of 6 h. The miotic responses in rabbit following administration of xyloglucan sols were compared with those from in situ gelling Pluronic F127 sols and from an aqueous buffer solution containing the same drug concentration. Sustained release of pilocarpine was observed with all gels, the duration of miotic response increasing with increase of xyloglucan concentration. The degree of enhancement of miotic response following sustained release of pilocarpine from the 1.5% w/w xyloglucan gel was similar to that from a 25% w/w Pluronic F127 gel.

Increased partitioning of pilocarpine to the oily phase of submicron emulsion does not result in improved ocular bioavailability.

Submicron emulsions containing pilocarpine as ion-pair with mono-dodecylphosphoric acid were prepared. Physical stability of these preparations was confirmed during 4 months of storage at 4 degrees C. Approximately 50% of the drug was found in the aqueous phase of emulsion separated using an ultrafiltration technique, while the rest was present in the oily phase and interphase. The miotic effect observed in rabbits after application of the ion-pair in aqueous solution or in submicron emulsion was the same; indicating that the drug distribution into the oily phase of the colloidal vehicle does not improve ocular bioavailability.

Micellar solutions of triblock copolymer surfactants with pilocarpine.

Solutions of surface active triblock copolymer Pluronic F127 in the vicinity of the critical micellar concentration (cmc) were prepared with or without pilocarpine (either as the hydrochloride salt or the free base) in water and phosphate buffer. The characteristics parameters of the surface activity (cmc, Gamma and a) were determined for F127 solutions. Additionally, it was found that the pilocarpine solutions without F127 in water exhibits a certain surface activity. The solutions containing F127 (2 wt.%) well above the cmc and pilocarpine (2 wt.% for the salt, or equimolar 1.7 wt.% for the base) were further tested in vivo (miotic response) on rabbit eye. Though the entrapment efficiency of the drug in the micelles was rather low (maximal 1.9%) the pharmacokinetic parameters (duration of miotic response and the area under miotic curve) were improved when compared to the standard pilocarpine solutions. The best results were obtained for the micellar pilocarpine base solution which exhibits significant prolongation of miotic activity and an increase of AUC for 64%.

A potential carrier based on liquid crystal nanoparticles for ophthalmic delivery of pilocarpine nitrate.

Poor corneal penetration and short preocular retention of a clinical hydrophilic drug, pilocarpine nitrate (PN), for the treatment of open-angle glaucoma and acute angle-closure glaucoma, limit its ocular application. The purpose of this study was to investigate the potential of liquid crystal nanoparticles (LCNPs) for ocular delivery of PN. LCNPs were developed by a top-down method using glyceryl monoolein (GMO) and water in the presence of stabilizer Poloxamer 407. They were characterized by transmission electron microscopy (TEM) and small angle X-ray diffraction (SAXS). The size of LCNP is 202.28±19.32 nm and the encapsulation efficiency reached 61.03%. The in vitro release profiles indicated that PN could keep sustained release from PN-loaded LCNPs for 8h. An ex vivo corneal permeation study revealed that the apparent permeability coefficient of PN-loaded LCNPs was 2.05-fold higher than that of commercial eye drops. In addition, the topical administration test showed that PN-loaded LCNPs had a prolonged effect on decreasing intraocular pressure (IOP) of rabbits compared with commercial drug and physiological saline. In conclusion, LCNPs had been demonstrated to be potential for controlled-release ocular drug delivery.

Design and evaluation of novel fast forming pilocarpine-loaded ocular hydrogels for sustained pharmacological response.

Fast forming hydrogels prepared by crosslinking a poly(ethylene glycol) (PEG)-based copolymer containing multiple thiol (SH) groups were evaluated for the controlled ocular delivery of pilocarpine and subsequent pupillary constriction. Physical properties of the hydrogels were characterized using UV-Vis spectrophotometry, transmission electron microscopy (TEM), rheometry, and swelling kinetics. Pilocarpine loading efficiency and release properties were measured in simulated tear fluid. The hydrogel formulations exhibited high drug loading efficiency (approximately 74%). Pilocarpine release was found to be biphasic with release half times of approximately 2 and 94 h, respectively, and 85-100% of the drug was released over 8-days. Pilocarpine-loaded (2% w/v) hydrogels were evaluated in a rabbit model and compared to a similar dose of drug in aqueous solution. The hydrogels were retained in the eye for the entire period of the study with no observed irritation. Pilocarpine-loaded hydrogels sustained pupillary constriction for 24 h after administration as compared to 3 h for the solution, an 8-fold increase in the duration of action. A strong correlation between pilocarpine release and pupillary response was observed. In conclusion, the current studies demonstrate that in situ forming PEG hydrogels possess the viscoelastic, retention, and sustained delivery properties required for an efficient ocular drug delivery system.