Metabolic fate of [14C]-ceftizoxime, a parenteral cephalosporin antibiotic, in rats and dogs.

The metabolic fate of (6R,7R)-7-[(Z)-2-(2-amino-4-thiazoyl)-2-methoxyiminoacetamido]-8-oxo-5-thia-1-a zabicyclo[4,2,0]oct-2-ene-2-carboxylic acid (ceftizoxime), a new cephalosporin antibiotic for injection, was investigated in rats and dogs after i.v. dosing. Ceftizoxime was rapidly and widely distributed in the whole body of rats except the brain. The concentrations were high in the serum as well as in the kidneys, liver, lungs, trachea and skin. A small amount of radioactivity passed the placenta. Serum levels of ceftizoxime declined with a half-life of 0.22 h in rats and 0.98 h in dogs. Most of the serum radioactivity was present as unchanged ceftizoxime in dogs. Urinary excretion was rapid and this elimination route was predominant in the two species. Small amounts of metabolites of ceftizoxime were found in the rat urine and bile, however, a major portion of the given dose was excreted in unchanged form. In dogs, ceftizoxime was resistant to metabolic degradation in the body.