Pharmacokinetics and pharmacodynamics of ceftizoxime in patients with dosages adjusted for renal function

Validation and Application of an LC-MS-MS Method for the Determination of Ceftizoxime in Human Serum and Urine

Ceftizoxime sodium is a third-generation cephalosporin available for parenteral administration, which is mainly excreted through urine. A rapid and sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method was developed and validated for the determination of ceftizoxime in human serum and urine. The samples were purified by protein precipitation and separated on an XTerra Phenyl column (4.6 × 50 mm, 5 µm). Electrospray ionization in the positive ion mode and multiple reaction monitoring were used to monitor the ion transitions at m/z 383.9/227.0. The results revealed that the method had excellent selectivity. The linear range covered from 2.50 to 10,000 ng/mL in serum and from 0.500 to 50.0 µg/mL in urine, respectively. Intra-batch and inter-batch precisions (in terms of relative standard deviation) were all <15% and the accuracies (in terms of relative error) were within the range of ± 15%. The lower limit of quantification, stability and extraction recovery were also validated and satisfied the criteria of validation. Finally, the method was successfully applied to a pharmacokinetic study of Chinese elderly healthy subjects after intravenous administration. The Cmax values in serum were 34,721.3 ± 5,697.3 ng/mL. Serum concentrations declined with t1/2 of 2.57 ± 0.22 h.

Human variability in the renal elimination of foreign compounds and renal excretion-related uncertainty factors for risk assessment

Renal excretion is an important route of elimination for xenobiotics and three processes determine the renal clearance of a compound [glomerular filtration (about 120 ml/min), active renal tubular secretion (>120 ml/min) and passive reabsorption (<120 ml/min)]. Human variability in kinetics has been quantified using a database of 15 compounds excreted extensively by the kidney (>60% of a dose) to develop renal-excretion related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [renal and total clearances, area under the plasma concentration time-curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was low for both routes of exposure, with coefficients of variation of 21% (oral) and 24% (intravenous) that were largely independent of the renal processes involved. Renal-excretion related uncertainty factors were below the default kinetic uncertainty factor of 3.16 for most subgroups analysed with the exception of the elderly (oral data) and neonates (intravenous data) for whom renal excretion-related factors of 4.2 and 3.2 would be required to cover up to 99% of these subgroups respectively.

Pharmacokinetics and pharmacodynamics of cefepime in patients with various degrees of renal function

This study evaluated the pharmacokinetics of cefepime in 36 patients with different levels of renal function. Pharmacokinetic and pharmacodynamic parameters were calculated using samples obtained at steady state. Patients with creatinine clearance (CL(CR)) of >100 ml/min had more rapid clearance (CL) and a lower minimum concentration in serum (C(min)). C(min) in this group was found to be 3.3 +/- 3.6 mg/liter (mean and standard deviation), compared to 19.5 +/- 21.5 mg/liter in patients with a CL(CR) of between 60 and 100 ml/min (P = 0.025) and 14.0 +/- 11.5 mg/liter in patients with a CL(CR) of <60 ml/min (P = 0.009). Patient data were also analyzed by the nonparametric expectation maximization method and Bayesian forecasting. The median volume of distribution in the central compartment was 27.08 liters. CL and CL(CR) were highly correlated (P = 0.00033) according to the equation CL= 0.324 liters/h + (0.0551 x CL(CR)). The median rate constants from the central compartment to the peripheral compartment and from the peripheral compartment to the central compartment were 12.58 and 41.09 h(-1), respectively. The time-concentration profiles for 1,000 patients (CL(CR)s, 120, 60, and 30 ml/min) each receiving various dosing regimens were simulated by using Monte Carlo simulations. Standard dosing resulted in a C(min) that was greater than or equal to the MIC in more than 80% of the simulated profiles with MICs < or = 2 mg/liter. Current dosing recommendations may be suboptimal for monotherapy of infections due to less susceptible pathogens (e.g., those for which MICs are > or = 4 mg/liter), particularly when CL(CR) exceeds 120 ml/min.