Store at -20°C under inert atmosphere. For maximum recovery of product, centrifuge the original vial prior to removing the cap.
References
Duckworth, C., et al.: J. Antimicrob. Agents Chemother., 31, 581(1993), Orwa, J., et al.: J. Pharm. Biomed. Anal., 23, 771 (2000), Platzer, D., et al.: J. Pharm. Biomed. Anal., 41, 84 (2006).