Stability Assessment of Extemporaneous Formulation of Amoxicillin for Parenteral Antimicrobial Therapy

Outpatient parenteral antimicrobial therapy (OPAT) is an important clinical tool in the treatment of severe infections away from the hospital setting. The stability of amoxicillin sodium in elastomeric infusion devices has been determined for parenteral antimicrobial therapy in the outpatient setting. Firstly, stability was studied at either ambient room temperature (25°C ±1), or at refrigerated temperature (4°C). The practice followed at Auckland City Hospital, to reduce manufacturing and delivery costs, is to order the infusion devices in batches of seven – therefore patients can have up to seven devices at home. A second set of experiments was therefore conducted where stability was assessed by simulating real life conditions to which the infusion devices are exposed. These include refrigerated storage for up to 6 days, followed by 24 hours at room temperature to mimic the patient administration period. The stability of amoxicillin was found to be improved when stored at 4°C compared to room temperature. However, significant concentration dependent degradation occurred after seven days; 87% degradation at 83.3 mg/mL down to 11.0 ±0.02 mg/mL, and 54% degradation at 25 mg/mL down to 11.5 ±0.01 mg/mL. Despite this, such formulations continue to be used successfully to treat patients with severe infections. The data generated from this study has been discussed alongside current clinical practice and observed patient outcomes.