Physical compatibility of 4% sodium citrate with selected antimicrobial agents

Purpose. The physical compatibility of 4% sodium citrate with vancomycin, gentamicin, tobramycin, daptomycin, and linezolid was evaluated. Methods. Admixtures were prepared by mixing 4% sodium citrate with clinically relevant concentrations of antimicrobial agents (vancomycin 5 mg/mL, vancomycin 10 mg/mL, vancomycin 20 mg/mL, daptomycin 5 mg/mL, gentamicin 2.4 mg/mL, tobramycin 2.4 mg/mL, and linezolid 1 mg/mL). Three samples of each admixture were incubated (1) at 22-23 degrees C and exposed to light, (2) in a water bath at 37 degrees C and exposed to light, (3) at 22-23 degrees C and protected from light, and (4) in a water bath at 37 degrees C and protected from light. Visual compatibility, spectrophotometric absorbance, and pH were evaluated immediately after mixing (baseline) and at 8, 24, and 48 hours. Physical compatibility was defined as the absence of visible precipitation, a pH value at 48 hours that did not vary by more than 10% from baseline, and an absorbance value of <0.015. Results. There was no visual evidence of precipitation and no clinically important changes in pH observed during the 48-hour study period in any admixture. However, turbidity, based on absorbance, was noted with vancomycin 20 mg/mL at each time point. Conclusion. No evidence of incompatibility was observed when vancomycin 5 mg/mL, vancomycin 10 mg/mL, daptomycin 5 mg/mL, gentamicin 2.4 mg/mL, tobramycin 2.4 mg/mL, or linezolid 1 mg/mL was mixed with 4% sodium citrate as might occur in an antimicrobial lock. Vancomycin 20 mg/mL mixed with 4% sodium citrate displayed spectrophotometric evidence of incompatibility.