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T.K. Winarko, B. Winarko, R. Varma; The Stability of Latanoprost in a Community Setting . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2187.
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Purpose: To determine the stability of 0.005% (50µg/ml) Latanoprost eye drops stored at room temperature (<25°C) four to six weeks after being dispensed to patients in a community setting. Methods: Consecutive patients previously on either monocular or binocular Latanoprost therapy were randomly assigned to receive Latanoprost either dispensed at the clinic or from a local pharmacy. The monocular and binocular treated patients were asked to return their bottles at the end of six and four weeks, respectively. No special instructions on storage of the bottles dispensed were given to the patient. All returned bottles were masked and the residual content was analyzed for latanoprost concentration using a reverse-phase HPLC technique. A group of bottles were filled with known volumes of latanoprost and sterile water and randomly interspersed with the bottles returned by the patients to serve as laboratory controls. Results: Of the 110 patients enrolled in the study, 89 patients returned their bottles. All bottles had been stored in a non-refrigerated area during the study (bedside, kitchen, bathroom). Of these 89 bottles, only 69 contained sufficient residual volume (200 µl) to conduct an HPLC analysis for latanoprost. Of the 69 bottles analyzed, 32 were dispensed from the clinic, and 37 were from the patients’ pharmacies; 29 had been used for 6 weeks and 40 for 4 weeks. HPLC analysis demonstrated that the mean concentration (± s.d.)of all samples (excluding controls) was 48.31 ± 2.31 µg/ml. The samples with the lowest concentrations of Latanoprost could result from numerous factors including: instability of the drug at room temperature, error in the HPLC method, or error in handling of the bottle resulting in instability of the drug. The patients enrolled in this study lived in the Southern California area where the average temperature during the study was 81°F (range 70°F to 95°F). No difference in latanoprost concentrations were found between those dispensed at the clinic compared to those obtained from the pharmacies. No difference in latanoprost concentrations were found between those samples used for four weeks and six weeks. Conclusion: In a "real world"community setting, the concentration of latanoprost 0.005% was maintained within the required limit (90% of labeled concentration) in the vast majority of patients. Furthermore, the site of dispensation of the drug or the length of use of the bottle (4 or 6 weeks) was not associated with any decrement in latanoprost stability.
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