Determination of ceftazidime concentration in Mueller Hinton agar by high-performance liquid chromatography

A simple and rapid RP-HPLC method for the direct determination of ceftazidime (a beta-lactam antibiotic) in agar (Mueller Hinton Agar-II) was developed. The method, characterised by good precision (C.V.less than or equal to 7.9%) and linearity in the 5-200 mu g/ml range (r(2) greater than or equal to 0.998), showed high recovery from agar (104+/-8%) and a sensitivity limit of 1.4 mu g/ml. The analytical procedure allowed the determination of the ''true'' antibiotic concentration in the agar matrix. In addition, the small volume sample may allow a precise evaluation of the antibiotic levels point by point in the agar plates necessary to study the kinetics of diffusion of ceftazidime.