The poor bioavailability and therapeutic response exhibited by the conventional ophthalmic solutions due to precorneal elimination of the drug may be overcome by the use of in situ gel forming systems that are instilled as drops into the eye and undergo a sol-gel transition in the cul-de-sac. Our present work describes the formulation and evaluation of an ophthalmic delivery system of an antibacterial agent, CPH, based on the concept of ion-activated in situ gelation. Gelrite gellan gum, a novel ophthalmic vehicle that gels in the presence of mono or divalent cations, present in the lacrimal fluid was used alone and in combinations with sodium alginate as the gelling agent. The developed formulations were therapeutically efficacious and provided sustained release of the drug over an 8-hr period in vitro.
Eye diseases can cause discomfort and anxiety in patients, with the ultimate fear of loss of vision and facial disfigurement. Many regions of the eye are relatively inaccessible to systemically administered drugs and, as a result, topical drug delivery remains the preferred route in most cases. Drugs may be delivered to treat the precorneal region for conjunctivitis and blepharitis, or to provide intraocular diseases such as glaucoma, uveitis, and cytomegalovirus retinitis. Most of the ophthalmic formulation strategies aim at maximizing ocular drug permeability through prolongation of the drug residence time in the cornea and conjunctival sac, as well as minimizing precorneal drug loss. The conventional topical ocular drug delivery systems show drawbacks such as increased precorneal elimination and high variability in efficacy. Attempts have been made to overcome these problems and enhance ocular bioavailability by the development of newer drug delivery systems. This review is concerned with classification, recent findings and applications and biocompatibility of newer drug delivery systems for the treatment of ocular diseases.
The present investigation concerns the development of floating matrix tablets of metoclopramide hydrochloride (MHCl) for improving its bioavailability by prolonging gastric residence time. Floating matrix tablets (FMT) of MHCl were prepared using the polymers guar gum (GG), karaya gum (KG), HPMC E15 (HE) alone and in combination with HPMC K15M (HK) and gas generating agents such as calcium carbonate and citric acid. The fabricated tablets were evaluated for their physical characteristics such as hardness, drug content, buoyancy, swelling properties and in vitro release studies in 0.1N HCl. The tablets without gas generating agents and HK did not float at all whereas tablets with gas generating agents and without HK floated for 2.33-5.48 h then eroded completely and exhibited faster drug release. Tablets with gas generating agents and HK floated for 24 h without complete erosion and showed slower drug release. This indicates that gas generating agents contributes towards the initial floating of tablets and faster drug release and HK for maintaining the integrity of the FMT and sustaining the drug release. The increase in the concentration of HK in FMT from 10 mg to 40 mg resulted in decrease in release rate of drug. The possibility of drug polymer interaction was determined by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectrometer, and confirmed no interaction between drug and polymers. The release pattern of prepared tablets followed Higuchi kinetics which confirms release mechanism by diffusion.
Film-type scleral implants of indomethacin with gellan gum were prepared by solvent casting and evaluated for uniformities of thickness, weight, drug content, and surface pH. The effect of plasticizers like glycerol, propylene glycol (PG), and polyethylene glycol 200, and 400 on the void volume of free gellan films (placebo) was calculated from the water content of the films. The drug release from the prepared implants was determined using a static dissolution set-up developed and optimized in our laboratory. Based on the results of the void volume and initial drug release studies, glycerol and PG were selected as the plasticizers for the gellan-based implants. The morphology of the drug-free films (containing 10% and 40% of PG) and the drug-loaded films (before and after dissolution and crosslinked) was studied using scanning electron microscopy. Further, the effect of plasticizer concentration, gellan concentration, effect of crosslinking technique, and duration of crosslinking using calcium chloride on in vitro drug release characteristics were evaluated. Selected batches of the implants were subjected to pharmacodynamic studies, after scleral placement, in uveitis-induced (intravitreal injection of bovine serum albumin 50 microg/ml) rabbit eyes. The release of indomethacin from the prepared implants followed matrix diffusion kinetics with diffusion co-efficient (n) values ranging between 0.358 to 0.708 and seemed to depend on both gellan and plasticizer concentration. Surface crosslinking with 10% calcium chloride for 8 hr retarded drug release (1.42 times less than noncrosslinked implant) and was optimum. The pharmacodynamic studies showed a marked improvement in the various clinical parameters (congestion, keratitis, flare, clot, aqueous cells, and synechias) in the implanted eye compared with the control eye in the rabbits. The scleral implants survived up to 3 weeks in vivo.
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