In vitro stability of fortified ophthalmic antibiotics stored at -20 degrees C for 6 months.

Purpose: This study evaluates the in vitro stability and sterility of fortified ophthalmic antibiotic preparations of 5% solutions (50 mg/mL) made from commercially available powders of amikacin, ceftazidime, and vancomycin stored at -20 degrees C for 6 months.

Methods: Antibiotic solutions were prepared with aseptic techniques by reconstitution and dilution of the commercially available powders (amikacin, ceftazidime, and vancomycin) and stored at -20 degrees C. After various durations of storage, the stability of various physical and chemical properties was determined by a pH meter, an osmometer, and high-performance liquid chromatography. Microbiological activity was assayed according to the European Pharmacopoeia.

Results: Solutions of 5% amikacin or ceftazidime in 0.9% sodium chloride and vancomycin in 5% dextrose were found to be physically, chemically, and microbiologically stable after storage at -20 degrees C for 190 days. A time limitation of 6 months is proposed.

Conclusion: Fortified ophthalmic antibiotic solutions prepared and supplied by a pharmacy can be stored in freezers at -20 degrees C for later use.