Stability of Sodium Ampicillin in Aqueous Solutions

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Abstract
A stability study of sodium ampicillin in aqueous solutions was carried out in order to determine the effects of various concentrations on the activity of the antibiotic with time. The need for such specific data is essential because the stability of the drug is not only very much dependent on its vehicle, pH and temperature, but also on its concentration. Sodium ampicillin was studied at various concentrations (0.5, 1, 1..5, 2, 3 and 4 g/100 ml) in 5% Dextrose Injection, U.S.P., and Sodium Chloride Injection, U.S.P., at 25 and 5 C. Each sample solution was colorimetrically assayed and its pH recorded for one week. Results indicated that the stability of the drug is definitely concentration dependent, especially in sodium chloride injection where the lower concentrations were more stable (94% potency for a 0.5 g/100 ml solution versus 85% potency for a 4.0 g/lOO ml solution after 24 hours at 25 C). All solutions at 5 C in Sodium Chloride Injection, U.S.P., were stable for 72 hours with the lower concentrations being more stable. A .5% Dextrose Injection, U.S.P., should not be used as a vehicle for sodium ampicillin, and if it is used, one should be aware that the solution is stable only for 4 hours at 5 C and less than 4 hours at 25 C.

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