Stability of Vancomycin and Ceftazidime With Prolonged Storage at-20 degrees C

BACKGROUND AND OBJECTIVE: Vancomycin and ceftazidime are commonly used intravitreal antibi-otics for suspected bacterial endophthalmitis. Many retina surgical practices prepare aliquoted individ-ual doses in syringes that are then stored frozen for future use, but this practice has not been well stud-ied. This investigation aims to examine the stability of frozen vancomycin and ceftazidime. MATERIALS AND METHODS: Samples of drugs were reconstituted monthly and placed in a-20 degrees C freez-er. At the end of 3 months and again at 6 months, a newly reconstituted drug constant was created and compared to a newly created reference sample. The frozen samples were compared to a freshly pro-duced drug solution. Using high-performance liq-uid chromatography (HPLC), the peak heights were compared to evaluate stability. RESULTS: The vancomycin reference sample was 100 +/- 1.67%. Values over time were 97.4 +/- 0.75%, 98.8 +/- 0.44%, 102.1 +/- 0.4%, 100.5 +/- 0.12%, 101.8 +/- 0.12, 101.5 +/- 0.11, and 100.6 +/- 1.87 for 1, 2, 3(A), 3(B), 4, 5, and 6 months, respectively. The ceftazidime refer-ence sample was 100 +/- 1.8%. Values over time were 100.7 +/- 1.78%, 100.0 +/- 1%, 102.3 +/- 1.55%, 117.5 +/- 11.6%, 112.8 +/- 1.64%, 123 +/- 2.8%, and 117 +/- 2.5% for 1, 2, 3(A), 3(B), 4, 5, and 6 months, respectively. CONCLUSION: Both vancomycin and ceftazidime were stable over 6 months under frozen conditions at-20 degrees C.