Stability of dicloxacillin sodium oral suspension stored in polypropylene syringes

The stability of dicloxacillin sodium in oral suspension stored in clear polypropylene oral syringes was studied. Commercially available dicloxacillin sodium powder for oral suspension from a single lot was reconstituted according to the manufacturer's instructions and drawn into 5-mL clear polypropylene oral syringes. The syringes were divided into groups and stored at -20, 4, 25, 40, 60 or 80 degrees C. Two additional lots were similarly reconstituted, repackaged, and stored at 80 degrees C only to assess interlot variability. Powder in the original containers was similarly reconstituted according to the manufacturer's instructions, and the containers were divided into groups and stored with the syringes. Immediately after reconstitution and at specified times during storage, three syringes and the original containers at each storage temperature were removed, and their contents were analyzed for dicloxacillin sodium concentration using the Standard USP Iodometric Assay. Dicloxacillin sodium follows a first-order rate of degradation at temperatures of 40, 60, and 80 degrees C. The rate of degradation changes to a zero-order process at temperatures of 25, 4, and -20 degrees C. At all temperatures, degradation occurred more rapidly when the drug was repackaged into unit dose polypropylene oral syringes than in the manufacturer's original container. Dicloxacillin sodium reconstituted from powder as oral suspension and repackaged in clear polypropylene syringes was stable for no longer than 7, 10, and 21 days when stored under ambient, refrigerated, and frozen conditions, respectively.