Stability of fluoxetine hydrochloride in fluoxetine solution diluted with common pharmaceutical diluents

The stability of fluoxetine hydrochloride in fluoxetine solution diluted with five common pharmaceutical diluents was studied. Fluoxetine syrup, containing fluoxetine 4 mg/mL (as the hydrochloride salt), was diluted to 1 and 2 mg/mL in each of the following: deionized water; Simple Syrup, British Pharmacopeia; Simple Syrup, USP; Aromatic Elixir, USP; and grape-cranberry drink. Each solution was divided into eight 120-mL amber glass bottles: four stored at 5 degrees C and four stored at 30 degrees C. Samples were removed from each bottle at time zero and two, four, and eight weeks and assayed in triplicate with high-performance liquid chromatographic methods for determining fluoxetine concentration and concentration of its primary degradation product, alpha-[2-(methylamino)ethyl]benzene methanol. Stability was established if the fluoxetine concentration changed by < 10% and if the concentration of the degradation product was < 1% of the initial fluoxetine concentration. No test mixture dropped below 95% of the initial fluoxetine concentration or exceeded 0.5% degradation product during the study period. Fluoxetine hydrochloride was stable for eight weeks in fluoxetine solution diluted to 1 or 2 mg/mL with common pharmaceutical diluents and stored at 5 or 30 degrees C.