High-performance liquid chromatographic assay for cefotiam and d3-cefotiam in human serum

Measurement of Free Plasma Concentrations of Beta-Lactam Antibiotics: An Applicability Study in Intensive Care Unit Patients

BACKGROUND

The antibacterial effect of antibiotics is linked to the free drug concentration. This study investigated the applicability of an ultrafiltration method to determine free plasma concentrations of beta-lactam antibiotics in ICU patients.

METHODS

Eligible patients included adult ICU patients treated with ceftazidime (CAZ), meropenem (MEM), piperacillin (PIP)/tazobactam (TAZ), or flucloxacillin (FXN) by continuous infusion. Up to 2 arterial blood samples were drawn at steady state. Patients could be included more than once if they received another antibiotic. Free drug concentrations were determined by high-performance liquid chromatography with ultraviolet detection after ultrafiltration, using a method that maintained physiological conditions (pH 7.4/37°C). Total drug concentrations were determined to calculate the unbound fraction. In a post-hoc analysis, free concentrations were compared with the target value of 4× the epidemiological cut-off value (ECOFF) for Pseudomonas aeruginosa as a worst-case scenario for empirical therapy with CAZ, MEM or PIP/tazobactam and against methicillin-sensitive Staphylococcus aureus for targeted therapy with FXN.

RESULTS

Fifty different antibiotic treatment periods in 38 patients were evaluated. The concentrations of the antibiotics showed a wide range because of the fixed dosing regimen in a mixed population with variable kidney function. The mean unbound fractions (fu) of CAZ, MEM, and PIP were 102.5%, 98.4%, and 95.7%, with interpatient variability of <6%. The mean fu of FXN was 11.6%, with interpatient variability of 39%. It was observed that 2 of 12 free concentrations of CAZ, 1 of 40 concentrations of MEM, and 11 of 23 concentrations of PIP were below the applied target concentration of 4 × ECOFF for P. aeruginosa. All concentrations of FXN (9 samples from 6 patients) were >8 × ECOFF for methicillin-sensitive Staphylococcus aureus.

CONCLUSIONS

For therapeutic drug monitoring purposes, measuring total or free concentrations of CAZ, MEM, or PIP is seemingly adequate. For highly protein-bound beta-lactams such as FXN, free concentrations should be favored in ICU patients with prevalent hypoalbuminemia.

Novel Population Pharmacokinetic Approach to Explain the Differences between Cystic Fibrosis Patients and Healthy Volunteers via Protein Binding

The pharmacokinetics in patients with cystic fibrosis (CF) has long been thought to differ considerably from that in healthy volunteers. For highly protein bound β-lactams, profound pharmacokinetic differences were observed between comparatively morbid patients with CF and healthy volunteers. These differences could be explained by body weight and body composition for β-lactams with low protein binding. This study aimed to develop a novel population modeling approach to describe the pharmacokinetic differences between both subject groups by estimating protein binding. Eight patients with CF (lean body mass [LBM]: 39.8 ± 5.4kg) and six healthy volunteers (LBM: 53.1 ± 9.5kg) received 1027.5 mg cefotiam intravenously. Plasma concentrations and amounts in urine were simultaneously modelled. Unscaled total clearance and volume of distribution were 3% smaller in patients with CF compared to those in healthy volunteers. After allometric scaling by LBM to account for body size and composition, the remaining pharmacokinetic differences were explained by estimating the unbound fraction of cefotiam in plasma. The latter was fixed to 50% in male and estimated as 54.5% in female healthy volunteers as well as 56.3% in male and 74.4% in female patients with CF. This novel approach holds promise for characterizing the pharmacokinetics in special patient populations with altered protein binding.

Development of breakpoints of cephems for intraabdominal infections based on pharmacokinetics and pharmacodynamics in the peritoneal fluid of patients

We developed breakpoints for cephem antibacterial agents for intraabdominal infections based on pharmacokinetics (PK) and pharmacodynamics (PD) at the target site. Cefepime (CFPM), cefotiam (CTM), cefozopran (CZOP), and flomoxef (FMOX) were each administered to 8-10 patients before abdominal surgery, and venous blood and peritoneal fluid (PF) samples were obtained. The drug concentrations in plasma and PF were determined and analyzed using population pharmacokinetic modeling. Using the pharmacokinetic model parameters, a Monte Carlo simulation was conducted to estimate the probabilities of attaining the bacteriostatic and bactericidal targets (40% and 70% of the time above the minimum inhibitory concentration (T > MIC), respectively) in PF. The bacteriostatic and bactericidal breakpoints were determined as the highest MIC values at which the bacteriostatic and bactericidal probabilities in PF were > or =80%, which values varied with drug and dosing regimen. Site-specific PK-PD-based breakpoints for CFPM, CTM, CZOP, and FMOX are proposed, and should help us to select appropriate cephems and design their dosing regimens for intraabdominal infections.

Cefotiam concentrations in the sinus fluid of patients with chronic sinusitis after administration of cefotiam hexetil

Cefotiam hexetil is a prodrug of cefotiam. The concentrations of cefotiam in plasma and sinus secretions were determined in 18 patients (10 males, 8 females, aged 39.3 +/- 13.0 years) with chronic sinusitis. All patients received two 200 mg oral doses of cefotiam hexetil 12 h apart and were divided into four groups according to the time which elapsed between the last dose and collection of secretion samples. The last dose was given 2 h (group I), 3 h (group II), 4 h (group III) or 6 h (group IV) before sinus puncture. Cefotiam concentrations were measured by high-pressure liquid chromatography and microbiological assay, results being very similar with both methods. Mean concentrations of cefotiam with the standard deviation in sinus exudates were 1.04 +/- 0.60 mg/l at 2 h (n = 6), 1.04 +/- 0.33 mg/l at 3 h (n = 4), 0.75 +/- 0.74 mg/l at 4 h (n = 4) and < 0.10 mg/l at 6 h (n = 4). Mean sinus fluid concentrations were higher than mean plasma concentrations in all groups. These results suggest that cefotiam concentrations higher than the MICs for common pathogens are found in sinus secretions up to 4 h after oral administration of cefotiam hexetil.

Automated high-performance liquid chromatographic method for the simultaneous determination of cefotiam and delta 3-cefotiam in human plasma using column switching

An automated high-performance liquid chromatographic method using column switching was established for the simultaneous determination of cefotiam (I) and delta 3-cefotiam (II) in human plasma after oral administration of cefotiam hexetil dihydrochloride. The method allowed the determination of analytes in plasma by the direct injection of diluted specimen with phosphate buffer. The analytes were enriched onto the C18 short pretreatment column by 0.05 M phosphate buffer (pH 7.7), while proteins and endogenous hydrophilic substances in plasma were washed off to waste. The enriched analytes were then back-flushed onto the analytical C18 column, separated by a mixture of 0.05 M phosphate buffer (pH 7.7)-acetonitrile (88:12, v/v) and detected by the ultraviolet absorbance at 254 nm. Recoveries from spiked plasma were quantitative, and the coefficients of variation were below 4%. The lower detection limits in plasma were 10 ng/ml for both I and II. Concentrations of I and II in plasma determined by the present method were in good agreement with those obtained by the conventional deproteinization method.