Solubility ocular solutions

Water-soluble polymers can also be used as aqueous solutions for drug delivery. Although the polymer is already dissolved, its increase in viscosity of the drug solution causes the drug to be retained somewhat longer in the desired application. This technique is common with ocular, nasal, and oral applications of drug solutions. 

A popular approach to improve ocular drag bioavailability is to incorporate soluble polymers into an aqueous solution to extend the drug residence time in the cul-de-sac. It is reasoned that the solution viscosity would be increased and hence solution drainage would be reduced. The more commonly used viscolyzing agents include PVA and derivatives of cellulose. Cellulosic polymers, such as methylcellulose, hydroxyethylcellulose (HEC), hydroxypropyl-methylcellulose (HPMC) and hydroxypropylcellulose (HPC), are widely used as viscolyzers showing Newtonian properties. They have common properties ... 

Ointments are commonly used for topical application of drugs to the eye.These vehicles are primarily mixtures of white petrolatum and liquid mineral oil with or without a water-miscible agent, such as lanolin.The mineral oil is added to the petrolatum to allow the vehicle to melt at body temperature, and the lanolin is added to the nonemulsive ointment base to absorb water. This allows for water and water-soluble drugs to be retained in the delivery system. Commercial ophthalmic ointments are derivatives of a hydrocarbon mixture of 60% petrolatum USP and 40% mineral oil USP, forming a molecular complex that is semisolid but melts at body temperature. In general, ointments are well tolerated by the ocular tissues, and when antibiotics are incorporated they are usually more stable in ointment than in solution. 

The ocular bioavailability of a topically applied drug (i.e. the percentage of effective drug available at the ocular surface or in the anterior segment) depends upon a number of factors. The acidic dissociation constant (pRa) of the drug and the pH of the vehicle determine the differential solubility of the drug on the ocular surface and its intraocular bioavailability. Increasing the concentration of buffer in ophthalmic solutions extends the time taken for the tear film to return... 

Sulfacetamide is the IV-acetyl derivative of sulfanilamide. The sodium salt of sulfacetamide, because of its effectiveness and low toxicity, continues to be the most widely prescribed sulfonamide in the form of eye-drops and ointment for ophthalmic infections. It was introduced in Europe as "Albucid" in 1938 for various eye and other topical infections. Since its use in the treatment of corneal ulcers (1), sulfacetamide is still popular in ophthalmology. The sodium salt is highly soluble at the physiologic pH of 7.4, and is especially suited, as a 10-30% solution, for repeated topical application in the local management of ophthalmic infections (2-4). It is used mainly in the treatment of acute conjunctivitis and in the prophylaxis of ocular infections after injuries or burns (5). Several reviews on various aspects of sulfacetamide have been published (6-10). 

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