Stability of gentamicin and tobramycin in concentrate solutions for automated peritoneal dialysis

Stability of gentamicin and tobramycin in 30 and 50% dextrose peritoneal dialysate concentrate (PDC) fluids was determined at room temperature. All solutions were prepared and stored at 23 degrees C and aliquots were obtained at 0, 1, 2, 4, 8, 12, 24, and 48 h. A degradation rate constant Kdeg was calculated from the concentration time curve of each solution. The length of time required for the gentamicin and tobramycin concentrations to decline to 90% of the initial concentration (t90) was also calculated. The Kdeg of gentamicin in all solutions was less than the Kdeg of tobramycin. The Kdeg increased markedly for gentamicin and tobramycin as the dextrose concentration increased in the PDC. Gentamicin is stable in the 30 and 50% PDC for at least 24 h at 23 degrees C. Tobramycin, however, demonstrated more than a 10% loss of activity in some PDC solutions. If tobramycin is to be added to PDC, especially the 50% dextrose solution, it should be used within 12 h after admixture.