Allen LV & Lo P
Stability of oral liquid penicillins in unit dose containers at various temperatures.

Am J Hosp Pharm, 36(2): 209-211, 1979
ISSN: 0002-9289 American Journal of Hospital Pharmacy (PubMed)

Abstract
The effect of freezing on the stability of reconstituted, unit dose packaged oral amoxicillin trihydrate and ampicillin suspensions and penicillin V potassium solutions was studied. Powders for suspension or solution of the three penicillins were reconstituted according to manufacturers' directions to yield a concentration of 250 mg/5 ml. Samples of 5 ml then were stored in amber, screw-cap, glass vials at 25 C, 5 C, 0 C, -10 C or -20 C for 5, 10, 20, 30 or 60 days. The concentration of active constituents remaining after storage was determined spectrophotometrically. All three penicillins retained at least 90% of their original activity for at least 60 days when stored at -20 C. Ampicillin and pencillin V potassium retained at least 90% of their activity after 60 days of storage at -10 C but amoxicillin concentration decreased to 88% and 87% of initial concentration after 60 days storage at -10 C and 0 C, respectively. Degradation appeared to be by a zero-order process for amoxicillin and ampicillin and by a first-order process for penicillin V potassium. It appears that oral solutions of amoxicillin, ampicillin and penicillin V potassium can be effectively stored for at least 50 days in a freezer at -10 C with little loss of activity.