Stability of Antibiotics for Use in the Testing of Immediate Drug Allergy Reactions

Limited information is available regarding the physicochemical stability of penicillin-based preparations for skin testing purposes, and no information is currently available for other classes of antibiotics.

To perform chemical and physical stability studies on 16 parenteral antibiotics for skin testing purposes, with an overall aim to provide practical recommendations to clinicians on suitable components, storage, and optimal shelf-life of such preparations.

Chemical stability was assessed via validated stability-indicating high performance liquid chromatography with ultraviolet detection assays, while absence of precipitations or haziness, significant pH shift, and color change were used to determine physical stability.

Other than amoxicillin/clavulanic acid, all of the parenteral antibiotics were found to have adequate physicochemical stability between 2 and 7 days. Amoxicillin in water for injection BP retained more than 90% stability, whereas amoxicillin/clavulanic acid dropped to less than 80%. Ampicillin remained more than 90% stable for 2 days, and benzylpenicillin, flucloxacillin, and piperacillin/tazobactam were stable for 2 days or more at approximately 95%. Cephalosporins were stable for 2 days, except ceftazidime, which increased to more than 110%. Aztreonam, ciprofloxacin, and vancomycin retained more than 95% stability for 7 days, whereas meropenem was stable for 2 days. Sulfamethoxazole/trimethoprim in plastic syringe lost 15% but stabilized at approximately 85% for 7 days. No precipitation occurred, but amoxicillin/clavulanic acid changed color by day 2. pH decreases of 1.0 unit or less were observed in penicillins, whereas cefepime dropped below acceptable pH limits by day 7. Absorbance shifts of more than 100 units were seen in several antibiotics by day 7.

This study has generated practical stability information for clinicians, allowing 15 parenteral antibiotics from 7 different classes to be aseptically prepared in advance for use in the testing of drug allergy reactions.