An Evaluation of Amoxicillin/Clavulanate Stability in Aqueous Systems, Including Its Suitability for Outpatient Parenteral Antimicrobial Therapy (OPAT)

Kamrin Kamalpersad, Giuseppe Luna, Bruce Sunderland, Petra Czarniak Discipline of Pharmacy, Curtin Medical School, Faculty of Health Sciences, Curtin University, Bentley, Western Australia, AustraliaCorrespondence: Petra Czarniak, Discipline of Pharmacy, Curtin Medical School, Faculty of Health Sciences, Curtin University, Kent Street, Bentley, Western Australia, 6102, Australia, Tel +61 89266 7419, Email [email protected]: Amoxicillin/clavulanate antibiotic combination is suitable for treating a range of infections, including some suited for Outpatient Parenteral Antimicrobial Therapy (OPAT). The aim of the study was to evaluate shelf-life values of amoxicillin at clinical concentrations in the presence of clavulanate for use in OPAT.Methods: A stability-indicating HPLC assay was developed and validated. Kinetic studies were performed at 1 mg/mL and 15 mg/mL amoxicillin at 40– 60 °C. Studies in elastomeric infusers included the pH lowered from 8.73 to 6.52 for 1 mg/mL; 8.85 to 7.69 for 7.5 mg/mL and 8.68 to 8.40 for 15 mg/mL amoxicillin plus clavulanate and stored at 2.9 °C.Results: Amoxicillin and clavulanate eluted at 5.2 and 3.0 minutes, respectively, with linear concentration relationships. Forced degradation retained base-line separation of each component in the presence of degradation products. Amoxicillin 1 mg/mL had a shelf-life of 4.85 hours at pH 6.53 and 40 °C which on extrapolation to 25 °C was 22.8 h. Clavulanate was 1.38 h at 40 °C and 4.0 h at 25 °C. Amoxicillin 15 mg/mL at pH 8.34 gave a shelf-life of 0.11 h at 40 °C and clavulanate 0.41 h. In elastomeric infusers, amoxicillin 1 mg/mL, with lowering pH from 8.73 to 6.52, improved the shelf-life at 2.9 °C from 72 to > 263.8 h and similarly for clavulanate. At 7.5 mg/mL amoxicillin, lowering pH from 8.85 to 7.69 improved the shelf-life from 4.2 to 51.8 h and clavulanate from 4.2 to 48.0 h. At 15 mg/mL amoxicillin, the shelf-life values at pH 8.68 or 8.40 were 3.8 h and 1.6 h and similarly for clavulanate.Conclusion: Amoxicillin and clavulanate showed adequate stability at 2.9 °C for OPAT storage at 1 mg/mL and possibly 7.5 mg/mL, but not 15 mg/mL. Low shelf-life values at 25 °C also limit administration times.Keywords: amoxicillin, clavulanate, stability, shelf-life, OPAT, infusers