Solution stability of cephradine neutralized with arginine or sodium bicarbonate

The solution stability of two formulations of cephradine--one using L-arginine and the other sodium carbonate as the neutralizer--was studied. Solutions of each formulation of 1% cephradine were prepared in the following diluents: 0.9% sodium chloride injection, lactated Ringer's injection, Ringer's injection, Normosol-R injection, 5% dextrose injection, and sterile water for injection; 5 and 25% solutions were made with sterile water for injection. All solutions were maintained at 25 degrees C, and at least five samples of each were assayed at various time intervals. Assay methods were HPLC, hydroxylamine colorimetric assay, microbiological agar diffusion, and iodometric analysis. By all assay methods, degradation rates of 1% solutions were lower for the arginine-neutralized product than for the one neutralized with sodium carbonate. This may be attributable to the lower pH values of solutions of the formulation with arginine, because one mechanism of degradation is pH-dependent. At concentrations of 5%, the difference in cephradine stability between the two formulations was minimal. At the 25% concentration, the formulations containing sodium carbonate were more stable. At these higher concentrations, the effect of pH is less important because degradation occurs by a combination of mechanisms. The 1% cephradine-arginine formulation was more stable than the same strength cephradine-sodium carbonate formulation in all the i.v. diluents studied. At 5 and 25% cephradine concentrations, the differences in stability between the two formulations were not substantial.