Stability of Cefpirome Sulfate in Aqueous Solutions.

The influence of pH on the stability of cefpirome sulfate was investigated in the pH range of 0.44 - 13.00. The degradation of cefpirome sulfate as a result of hydrolysis was a pseudo-first-order reaction. General acid-base hydrolysis of cefpirome sulfate was not observed. In the solutions of hydrochloric acid, sodium hydroxide, acetate, borate and phosphate buffer, k(obs) = k(pH) because specific acid-base catalysis was observed. Specific acid-base catalysis of cefpirome sulfate consisted of the following reactions: hydrolysis of cefpirome sulfate catalyzed by hydrogen ions (kH+), hydrolysis of dications (k₁H₂O) monocations (k₂ H₂O), zwitter ions (k₃H₂O) and monoanions (k₄ H₂O) of cefpirome sulfate under the influence of water. The total rate of the reaction was equal to the sum of partial reactions k(pH) = kH+ x aH+ + kH₂O x f₁ + k₂H₂O x f₂ + k₃H₂O x f₃ + k₄ H₂O x f₄. Based on the dependence k(pH) = f(pH) it was found that cefpirome sulfate was the most stable in aqueous solutions in the pH range of 4-6.