Thursday, 26 November 2015

Formulations of Ophthalmic: Notes For GPAT preparation

Ophthalmic preparations are the products which are intended for the application to th eye. Generally, they are used for the treatment of disease, for pain relief or for a diagnostic purpose.
There are many excipients used while manufacturing of ophthalmic. Below we have classified different excipients used in an ophthalmic preparation.

1. Drop size and dosage: Average volume of human tear drop is approximately 7 microlitres and the maximum volume that can be held by the eye is 30 microlitres. A normal dose administered through a drop of dropper of an ophthalmic preparation is 50 microlitres.

2. Viscosity enhancers: Increasing the viscosity results in increasing the residence time of the preparation in the eyes which ultimately leads to enhanced bioavailability of the drug.

Common viscosity enhancing agents include: Methyl cellulose derivatives, Polyvinyl alcohol, Povidone, Dextran, Macrogol.

3. pH and buffering capacity: The pH of human tear in normal conditions is 7.2. Usually an ophthalmic preparation of pH range 3.5-10.5 is tolerable.

 Buffering agents used in the ophthalmic preparation: Borate, Phosphate and citrate buffers.

4. Tonicity: For less irritation an ophthalmic should have tonicity equivalent to 0.9% solution of NaCl.
Tonicity adjusters used in the formulation include: NaCl, KCl, Glucose, Glycerol etc.

5. Wetting and spreading agents: Polysorbate 80 (Non-ionic surfactants are less toxic to eye than cationic and anionic surfactants).

6. Stabilisers: Stabilisers are used for the purpose of preventing the ophthalmic preparations from oxidative degradation.

Most common antioxidants are: Sodium metabisulphite and Sodium sulphite.
Ascorbic acid and Acetyl cysteine are used in phenylephrine formulations.
Chelating agents such as EDTA can be used to reduce the oxidative damage caused by metal impurities.

7. Sterility and preservatives: Ophthalmic solutions are generally sterilized either by autoclaving (1210 C for 15 minutes) or by bacteria retentive filters.

 Common preservatives used in ophthalmic solutions are:  Benzalkonium chloride (0.03%), Benzethonium chloride (0.01%), Chlorobutanol (0.5%), Phenyl mercuric acetate (0.004%), Phenyl mercuric nitrate (0.004%) and Thiomersal (0.01%).

  • A mixture of Benzalkonium chloride (0.01%) and Polymyxin B sulphate is used against pseudomonas aeruginosa (cause ulceration and blindness). Benzalkonium chloride (0.01%) and disod. edetate (0.01 to .1 %) can also be applied for the same purpose. 

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5.  Miscellaneous topics for GPAT

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