The determination of the ionization profile of ceftazidime

Abstract

The ionization constants (pKa) of ceftazidime, third generation cephalosporin, were determined by potentiometry. Ceftazidime is an ampholyte with four ionizable centers, three acidic centers (two carboxyl groups and amide group) and one basic center (aminothiazole). Potentiometric determinations were performed at 25 °C and constant ionic strength of 0.1 M (NaCl). Experimental data were analyzed by computer software Hyperquad and four pKa values were derived: pKa1 2.55; pKa2 3.94; pKa3 4.54 and pKa4 7.55. According to the obtained pKa values distribution diagram as a function of pH was constructed and distribution of the ceftazidime equilibrium forms was calculated at a pH values of biopharmaceutical significance (pH 1.2, 4.5, 6.8 and 7.4). In addition, based on the chemical structure of ceftazidime the order of ionization were suggested.