Clinical pharmacokinetics of the third generation cephalosporins

At the present time, the third generation cephalosporins that are already on the market or close to this point include cefsulodin, cefotaxime, cefoperazone, latamoxef, ceftriaxone, ceftazidime, ceftizoxime and cefotetan. Other newer compounds are also under development but have not been included in this review. None of the third generation compounds is suitable for oral administration and, accordingly, their pharmacokinetics have been studied only after intravenous and intramuscular administration. Microbiological assays and HPLC methods have been used for the measurement of plasma/serum, urine, bile and cerebrospinal fluid (CSF) concentrations. As found with cefotaxime, microbiological assays should only be used when the full metabolite spectrum of a particular drug is known, as otherwise, the presence of microbiologically active metabolites may lead to erroneous conclusions. Under normal conditions, the major route of elimination is via the kidneys for cefsulodin, latamoxef, ceftazidime, ceftizoxime and cefotetan. In contrast, cefoperazone is mainly eliminated in the bile, whereas cefotaxime and ceftriaxone depend both on the liver and the kidneys for their elimination. With the exception of ceftriaxone, which has a longer elimination half-life (i.e. around 8 hours), all the other third generation cephalosporins have a t1/2 ranging between 1.5 and 2.5 hours. Plasma protein binding is variable from one compound to another. However, the clinical relevance of this parameter is not clearly established since tissue penetration also depends on the relative affinity of the drug for tissue components. Third generation cephalosporins seem to penetrate adequately into the CSF and, thus pharmacokinetically appear to be appropriate agents for the treatment of meningitis. The degree of modification of pharmacokinetic parameters by renal insufficiency or hepatic diseases depends, as for other drugs, on the extent to which the compound is excreted via the kidneys or the liver. The third generation cephalosporins have been extensively studied under these conditions and recommendations for dosage modification in special circumstances are available for most of them. The pharmacokinetics of some third generation cephalosporins may be modified in neonates and elderly patients. Accordingly, their use at the extremes of age must be accompanied by a closer than usual clinical monitoring of the patient. From a clinical point of view, the third generation cephalosporins possess reliable pharmacokinetic properties.(ABSTRACT TRUNCATED AT 400 WORDS)