Physical compatibility, antimicrobial activity, and stability of cefazolin combined with gentamicin or ethanol in sodium citrate as a catheter lock solution

Background: Catheters provide vascular access for patients requiring intravenous treatments, but frequently are a source of infection and/or thrombosis. Instilling a solution of an antimicrobial agent with an anticoagulant into the catheter lumen may salvage-infected catheters. Objective: The aim is to evaluate the physical compatibility, antibacterial activity, and stability of varying combinations of cefazolin (10 mg/mL), 40% ethanol, 4% sodium citrate with or without gentamicin (1 mg/mL) as a catheter lock solution over 48 h. Methods: Admixtures were prepared using aseptic technique and stored under four conditions with or without light at 25 degrees C or 37 degrees C. Prepared admixtures were assessed for physical compatibility, antimicrobial susceptibility, and chemical stability in triplicate at 0, 24 and 48 h. Admixture physical compatibility was determined by visual clarity, pH, and ultraviolet (UV) spectroscopy. Antibacterial activity was determined using the Kirby-Bauer disk diffusion method. The chemical stability of cefazolin and gentamicin were assessed using high performance liquid chromatography and UV spectroscopy, respectively. Results: All admixtures maintained clarity for 48 h. All admixtures stored at 25 degrees C and the admixture containing 10 mg/mL cefazolin-4% sodium citrate stored at 37 degrees C sustained antimicrobial activity and were chemically stable. A significant change in pH, antimicrobial activity, cefazolin concentration (<95% of baseline), were observed in admixtures containing ethanol stored at 37 degrees C after 24 h. Gentamicin concentrations remained stable throughout the study. Conclusion: The admixture of 10 mg/mL cefazolin-4% sodium citrate sustained antimicrobial activity over 48 h and was chemically stable. However, admixtures containing ethanol stored at 37 degrees C showed incompatibility with decreased antibacterial activity and cefazolin degradation after 24 h.