Pharmacokinetics of ceftizoxime
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The kinetics of ceftizoxime, a newly developed cephalosporin, were evaluated in 6 healthy subjects, with respect to its excretory pathways especially by the biliary route. Total, renal and biliary clearance were determined at two different steady states. Steady state was achieved by constant intravenous infusion (604.1 mg/h) over 6 h after an initial loading dose (750 mg); 1.5 h after discontinuation of that infusion, a further infusion was commenced at a lower rate (284 mg/h) over 3 h, the second steady state being reached 0.5 to 1.0 h later.
The drug was mainly excreted by the kidneys (56.7 to 92.9% of the dose). Biliary excretion, measured by the duodenal perfusion and marker dilution technique, was low (0.2 to 7.8% of the dose). Urinary and biliary excretion as well as total clearance were not dose-dependent. However, there was pronounced interindividual variation in total (35.2 to 236 ml/min) and renal clearance (10.6 to 208 ml/min), which could both be explained by varying interindividual urinary flow rates (mean flow rate: 0.99 ml/min to 3.14 ml/min).
Intraindividual variation in renal clearance was less pronounced, but in the same subject changes in renal clearance were correlated with changes in urinary flow rate. From the varying renal clearance, which exceeded the glomerular filtration rate at high urinary flow rates and was below it at low urinary flow rates, it can be concluded that, in addition to glomerular filtration, tubular secretion and tubular reabsorption are involved in the renal excretion of ceftizoxime.
The half-life calculated from two point estimates after discontinuation of the infusion at the higher rate tended to be longer in subjects with high total clearance (e. g. 1.4 h, clearance 223 ml/min) and shorter in subjects with low total clearance (e.g. 0.85 h, clearance 35.2 ml/min). From this it is concluded that the true half-life was not observed after discontinuation of the infusion.
Key wordsceftizoxime cephalosporins renal excretion tubular reabsorption tubular secretion healthy volunteers biliary excretion clearance studies
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