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R.M. Schwarcz, M. Dweck, H. Shah, S. Chilukuri; Liposomal Formulation of Phenylephrine Hydrochloride for a Time Release Sympathomimetic Activation of Muller's Muscle in Rabbit Model for Ultimate Ptosis Relief . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3443.
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Purpose: To create a liposomal formulation of Phenylephrine Hydrochloride for a time release activation of Muller's muscle in rabbits Methods: A liposomal mixture containing phosphatidylcholine 31.5 micromoles made from egg yolk, Stearylamine 9 micromoles, and Cholesterol 4.5 micromoles was created (purchased from sigma-aldrich). The mixture was dissolved into .5 ml of chloroform, and placed into a round bottom flask with glass beads. The solution was then evaporated using a rotavap. A thin film remained in the flask, at which point .2 ml of a 25 mg/ml solution of phenylephrine hydrochoride was added, shaken and sonicated for six hours. A resulting mixture of 28.9 mg/ml of lipid was left with 5mg/ml of phenylephrine hydrochloride. This was repeated using the same lipid content and .4 ml sample of the drug, and again with 1ml of the drug. Thus having strengths of 10mg/ml, and 25mg/ml respectively. A .5 ml solution is injected into the tarsus of dutch rabbit right eye, and the subtenon's space .5 ml as well. This is repeated in the right eye of two rabbits for each strength totalling six rabbit eyes. The left eye of each rabbit remained as a control. The length of pupillary dilation was noted for each rabbit on an hourly basis. Results: The rabbits that recieved the liposomal/drug mixture containing 5mg/ml remained in the dilated state for 2 hours. Those that recieved the mixture containing 10mg/ml of drug exhibited dilation for 13 hours, and the liposomal mixture containing 25 mg/ml remained dilated for 14 hours. Conclusions: The process of forming postively charged multilamellar liposomes of phenylephrine hydrochloride exhibited prolonged drug action. The implications for this could be promising clinically to aid in a mild 2-3mm ptosis correction for certain patients who's eyelid droop was variable throughout the day (myasthenia gravis for example). The sympathetic activation of muller's muscle is responsible for this 2-3 mm of lid elevation. Phenylephrine hydrochloride, when given topically would dilate the eye as well as activate this muscle, but is limited due to its short acting capabilities. Based on passed studies, a positively charged liposome was thought to be most beneficial do to the negatively charged ph of the ocular surface contents. Based on this idealogy, a time release phenylephrine hydrochloride was created. It is possible that the 5mg/ml mixture did not encapsulate into the liposome. Further studies will be performed to attempt to increase the length of drug action.
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