Stability ophthalmic suspensions

Suspension. If the drug is not sufficiently soluble, it can be formulated as a suspension. A suspension may also be desired to improve stability, bioavailability, or efficacy. The major topical ophthalmic suspensions are the steroid anti-inflammatory agents prednisolone acetate, dexamethasone, fluorometholone, and rimex-olone. Water-soluble salts of prednisolone phosphate and dexamethasone phosphate are available however, they have a lower steroid potency and are poorly absorbed. 

Povidone can also be used as a sedimentation stabilizer in ophthalmic suspensions. Mefenamic acid suspension is a typical example [492]. 

Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

Behind the relatively straightforward compositional nature of ophthalmic solutions, suspensions, and ointments, however, lie many of the same physicochemical parameters that affect drug stability, safety, and efficacy, as they do for most other drug products. But additionally, specialized dosage forms present the ophthalmic product designer with some extraordinary compositional and manufacturing challenges. These... 

The therapeutically inactive ingredients in ophthalmic solution and suspension dosage forms are necessary to perform one or more of the following functions adjust concentration and tonicity, buffer and adjust pH, stabilize the active ingredients against decomposition, increase solubility, impart viscosity, and act as solvent. The use of unnecessary ingredients is to be avoided, and the use of ingredients solely to impart a color, odor, or flavor is prohibited. 

The following conclusions can be offered at the end of this brief review. Emulsion systems, particularly, mtcroemulsions, seem to be developing rapidly toward commercial applications and possibly will become the vehicles of choice for lipid-soluble ophthalmic drugs. Traditional suspensions, used for ocular administration of drugs both water- and lipid-insoluble, after some initial uncertainties have apparently reached a stale of technical perfection. However, both emulsions and suspensions are not exempt of drawbacks and problems such as stability, sterilization, bioavailability. etc., which may limit their practical usefulness. 

Uses Tablet binder/disintegrant, excipient, suspension stabilizer in pharmaceuticals complexing agent detoxifier adsorbent in thin-iayer chromatography clarifier, filter aid, shelf life enhancer in beer, wine Regulatory FDA approved for implants, ophthalmics, orals, injectables, topicals NF, BP, EP compliance... 

Among single drug component studies, usual vehicles for dilution are 5% dextrose (D5W), 0.9% sodium chloride (normal saline, NS), aqueous buffers, peritoneal dialysis fluid, nonaqueous solvents, water for injection, phosphate-buffered saline, bacteriostatic water for injection, bacteriostatic sodium chloride. Ringer s injection, and lactated Ringer s. Stability studies can also be carried out on the drug product solution as such or in specific containers or injection devices. Solutions and suspensions can also be prepared extemporaneously and stability tested to show worthiness for oral, ophthalmic, or rectal administration. The following is an example of the first... 

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