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Oseltamivir phosphate (OSEL) is prescribed to manage influenza virus A, influenza virus B, and H1N1. OSEL capsule (75mg) was manufactured by GPO, Thailand under the trade name of A-FluTM. Some patients such as children cannot take oral solid dosage forms and need oral liquid preparations. In those cases, pharmacists prepare OSEL extemporaneous suspensions (OSEL ES). However the stability of OSEL ES in a tropical country such as Thailand has not been investigated. Then the stability of OSEL ES used in Queen Sirikit National Institute of Child Health (QSNICH), Bangkok Thailand was investigated. Solution of 10 mg/ml OSEL ES were compounded and stored in three different temperature conditions; room temperature, refrigerated temperature (7 ± 3 °C) and accelerated temperature (45 ± 5 °C). Triplicate samples were periodically taken for 12 weeks and assayed by high-performance liquid chromatography. All of the samples stored under room temperature and refrigerated conditions showed more than 90% of their initial concentrations of OSEL remained throughout the course of the study. For the accelerated temperature 62.91% of the initial concentration of OSEL remained at 12th week, which was significantly lower than the other conditions (p < 0.05). In addition, samples stored at 45 ± 5 °C showed changes in color and reductions in pH over the course of the experiment. In conclusion temperature above room temperature should be included for stability testing of extemporaneously prepared suspensions in tropical climates.
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