Stability of benzylpenicillin for continuous intravenous infusions: An isotonic formulation for therapeutic use and a low-dose formulation for clinical trial

Introduction: The objectives of this study were to develop a stability-indicating high performance liquid chromatography (HPLC) assay for benzylpenicillin (BPC) in pharmaceutical fluids, and to investigate the stability of (i) isotonic citrate-buffered BPC solutions at the clinically relevant concentration of 30 mg/mL, and (ii) low concentration citrate-buffered BPC intravenous infusions (5–30 μg/mL). Methods: The stability of isotonic BPC solutions containing 3.4 or 7.2 mg/mL sodium citrate was compared against contemporary hypertonic solutions. The HPLC assay was shown to be stability-indicating following acidic, alkali, oxidative and elevated temperature stress testing. Results: After 7 d storage at 4 °C and 24 h at 35 °C, the concentrations of isotonic BPC 30 mg/mL solutions containing 3.4 and 7.2 mg/mL sodium citrate were 96% and 95% respectively, compared to day 0. After 3 d at 4 °C and 24 h at room temperature (22 °C), the concentrations of isotonic BPC solutions with 3.4 and 7.2 mg/mL sodium citrate were 99% and 96% respectively, compared to day 0. These data were comparable to the hypertonic solutions and meet pharmacopeial stability requirements. Low concentration BPC infusions showed 0.5% and 2.5% degradation after 24 h storage at 22 °C and 35 °C, respectively. Conclusions: The isotonic BPC 30 mg/mL formulation is simple to prepare and may offer clinical benefits in settings where hypertonic solutions are problematic. This study provides assurance that high- and low-dose isotonic BPC infusions are stable at room temperature and our findings may be applicable to in vitro studies of BPC.