Effect of renal function and dialysis on temocillin pharmacokinetics

Binding of temocillin to plasma proteins in vitro and in vivo: the importance of plasma protein levels in different populations and of co-medications

BACKGROUND

Temocillin plasma protein binding (PPB) in healthy individuals is reported to be ∼85% but had not been studied in patients.

OBJECTIVES

To obtain normative data on temocillin PPB in patients in relation to infection and impact of co-medications widely used in ICU.

METHODS

Plasma was obtained from healthy individuals (Group #1), non-ICU patients with UTI (Group #2), ICU patients with suspected/confirmed ventriculitis (Group #3) or with sepsis/septic shock (Group #4). Total and unbound temocillin concentrations were measured in spiked samples from temocillin-naive donors (in vitro) or in plasma from temocillin-treated subjects (in vivo). The impact of diluting plasma, using pharmaceutical albumin, or adding drugs potentially competing for PPB was tested in spiked samples. Data were analysed using a modified Hill-Langmuir equation taking ligand depletion into account.

RESULTS

Temocillin PPB was saturable in all groups, both in vitro and in vivo. Maximal binding capacity (Bmax) was 1.2-2-fold lower in patients. At 20 and 200 mg/L (total concentrations), the unbound fraction reached 12%-29%, 23%-42% and 32%-52% in Groups #2, #3, #4. The unbound fraction was inversely correlated with albumin and C-reactive protein concentrations. Binding to albumin was 2-3-fold lower than in plasma and non-saturable. Drugs with high PPB but active at lower molar concentrations than temocillin caused minimal displacement, while fluconazole (low PPB but similar plasma concentrations to temocillin) increased up to 2-fold its unbound fraction.

CONCLUSIONS

Temocillin PPB is saturable, 2-4-fold lowered in infected patients in relation to disease severity (ICU admission, hypoalbuminaemia, inflammation) and only partially reproducible with albumin. Competition with other drugs must be considered for therapeutic concentrations to be meaningful.

Influence of Continuous Ambulatory Peritoneal Dialysis on Elimination of Drugs

Renal failure delays elimination of many drugs thus prolonging their half lives. By knowing the half life and distribution volume, one can estimate total plasma clearance. When measured values have not been reported, endogenous total plasma clearance can be estimated and compared with peritoneal clearance to determine the effect of CAPD on half life. When peritoneal clearance has not been reported, it can be estimated knowing molecular mass and unbound plasma fraction. Such estimates suggest that elimination kinetics of most drugs are not appreciably affected by CAPD. Compared to those of untreated anuric patients, plasma levels of carbenicillin, ticarcillin, some cephalosporins, all aminoglycosides, vancomycin, sfluorocytosine, amantadine, atenolol, sotalol, timolol, chlorpropamide, theophylline and lithium may be reduced somewhat by CAPD. Thus one should monitor plasma levels of these agents to insure therapeutic concentrations rather than simply following the dosage guidelines for anuric patient.

Temocillin dosing in haemodialysis patients based on population pharmacokinetics of total and unbound concentrations and Monte Carlo simulations

Objectives

To develop a population model describing temocillin pharmacokinetics (PK) in patients undergoing haemodialysis and investigate how pharmacokinetic/pharmacodynamic (PD) targets can be met with different dosage regimens.

Patients and methods

Sixteen patients received the currently licenced dosing of 1, 2 or 3 g of temocillin (total of 61 doses) corresponding to an inter-dialytic period of 20, 44 or 68 h, respectively, and a dialysis period of 4 h. A non-linear mixed-effects model was developed jointly for total and unbound temocillin serum concentrations. The performance of clinically feasible dosing regimens was evaluated using a 5000-subject Monte Carlo (MC) simulation for determining the highest MIC for which the PK/PD target of 40%ƒT>MIC would be reached in 90% of patients [probability of target attainment (PTA)]. This PK study was registered at ClinicalTrials.gov (NCT02285075).

Results

Temocillin unbound and total serum concentrations (429 samples) were used to fit an open two-compartment model with non-linear albumin binding and first-order elimination. In addition to total body clearance, dialysis clearance was modelled using the Michaels function. The currently licenced dosing achieved a 90% PTA for an MIC up to 8 mg/L. A new temocillin dosage regimen was designed that would achieve a 90% PTA for an MIC of 16 mg/L (MIC90 of target organisms) adjusted to patient weight and inter-dialytic period.

Conclusions

Currently licensed dosage regimen is suboptimal for MICs >8 mg/L (frequently found in clinical isolates). Model-based simulations allowed suggestion of a new dosage regimen with improved probability of microbiological success, applicability in routine clinical practice and more appropriate for empirical therapy.

Thrice-weekly temocillin administered after each dialysis session is appropriate for the treatment of serious Gram-negative infections in haemodialysis patients

In patients with end-stage renal disease (ESRD) treated with intermittent haemodialysis, a limited number of antibiotics have been studied for their suitability for parenteral administration after dialysis sessions only in a thrice-weekly regimen. Temocillin is a β-lactam antibiotic with a long half-live and enhanced activity against most Gram-negative bacteria, including extended-spectrum β-lactamase-producers, thus making it an ideal candidate for use in this setting. This study aimed to evaluate the reliability of thrice-weekly parenteral temocillin in haemodialysis patients by characterising the pharmacokinetics of total and free temocillin. Free and total temocillin concentrations were determined with a validated HPLC method in 448 samples derived from 48 administration cycles in 16 patients with ESRD treated with intermittent haemodialysis and temocillin. Pharmacokinetics were non-linear partly due to saturation in protein binding. Median clearance and half-life for the free drug during intradialysis and interdialysis periods were 113 mL/min vs. 26 mL/min and 3.6 h vs. 24 h, respectively, with dialysis extracting approximately one-half of the residual concentration. The free temocillin concentration remained >16 mg/L (MIC90 threshold for most Enterobacteriaceae) during 48%, 67% and 71% of the dosing interval for patients receiving 1 g q24h, 2 g q48h and 3 g q72h, respectively, suggesting appropriate exposure for the two latter therapeutic schemes. Temocillin administered on dialysis days only in a dosing schedule of 2 g q48h and 3 g q72h is appropriate for the treatment of serious and/or resistant Gram-negative infections in patients with ESRD undergoing intermittent haemodialysis. These doses are higher than those previously recommended.

Development and validation of a high performance liquid chromatography assay for the determination of temocillin in serum of haemodialysis patients

Therapeutic drug monitoring of β-lactams can be useful for the optimization of therapy, especially when little reference data exist on actual pharmacokinetic profiles such as in patients undergoing haemodialysis. There is no reported validated method for temocillin assay in serum samples, and preliminary studies evidenced potential for interferences by acidic metabolites and co-administered drugs in patients with advanced kidney failure. This paper describes a fully validated method for the determination of temocillin in human serum, and its applicability in haemodialysis patients. Temocillin was extracted from human serum by a solid phase extraction methodology, and then assayed by reversed-phase HPLC with UV-detection. The method was validated according to the accuracy profile methodology, using total error to verify the trueness, precision and overall accuracy. It showed high specificity and precision and was accurate in the concentration range of 5-400 mg/L. LOD and LOQ were 1.2 and 5 mg/L, respectively. No interference with 30 co-administered drugs was evidenced. The method was successfully applied to clinical samples from haemodialysis patients, showing a high degree of dialysability of temocillin.