Systematic comparison of the population pharmacokinetics and pharmacodynamics of piperacillin in cystic fibrosis patients and healthy volunteers

Pharmacokinetics of intravenous piperacillin administration in patients undergoing on-line hemodiafiltration

The pharmacokinetic characteristics of piperacillin sodium were studied in five volunteers undergoing on-line hemodiafiltration (HDF). The subjects were given 2 g of piperacillin sodium intravenously over 1 min and placed on on-line HDF for 4 h starting at 60 min after the piperacillin infusion. Noncompartmental models were employed for estimation of the pharmacokinetic parameters, and intradialytic piperacillin clearance was calculated by the recovery method. The mean volume of distribution and the elimination half-life were 0.27 +/- 0.13 liter/kg (mean +/- standard deviation) and 1.1 +/- 0.6 h, respectively. The total body clearance of piperacillin was 0.19 +/- 0.08 liter/h/kg. Piperacillin clearance through on-line HDF was 0.11 +/- 0.06 liter/h/kg. The mean serum piperacillin concentration was 4.0 +/- 1.9 microg/ml at the end of the 4-h on-line HDF session. The concentration of infused piperacillin recovered in the dialysate was 527 +/- 236 mg (26.3% +/- 11.8%). We suggest the replacement of 500 mg of piperacillin after each on-line HDF session.

Modeling the autoinhibition of clarithromycin metabolism during repeated oral administration

Clarithromycin decreases CYP3A4 activity and thus gradually inhibits its own metabolism as well as that of coadministered drugs. The aim of this study was to obtain an understanding of the time course of these changes. The plasma concentration-time profiles of clarithromycin and its active metabolite, 14(R)-hydroxy-clarithromycin, in 12 young healthy volunteers after oral administration of a clarithromycin suspension (500 mg twice a day [b.i.d.] for seven doses) were modeled by population pharmacokinetic analysis in the NONMEM program. The nonlinearity of clarithromycin metabolism was considered during model development, and the metabolite disposition kinetics were assumed to be linear. The absorption kinetics of clarithromycin were best described by a Weibull function model. The pharmacokinetics of clarithromycin and its 14(R)-hydroxyl metabolite were adequately described by a one-compartment model each for clarithromycin and its metabolite as well as an inhibition compartment that reflects the autoinhibition of clarithromycin metabolism. Up to 90% of the apparent total clarithromycin clearance (60 liters/h) was susceptible to reversible autoinhibition, depending on the concentration in the inhibition compartment. The proposed semimechanistic population pharmacokinetic model successfully described the autoinhibition of clarithromycin metabolism and may be used to adjust the doses of other drugs that are metabolized by CYP3A4 and that are coadministered with clarithromycin. Simulations showed that for the standard dose of 500 mg b.i.d., no further increase in the level of exposure occurs after approximately 48 h of treatment. For a 1,000-mg b.i.d. dose, the achievement of steady state is expected to take several days and to achieve a 3.6-fold higher level of clarithromycin exposure than the 500-mg b.i.d. dose. This evaluation provides a rationale for safer and more effective therapy with clarithromycin.

Bone penetration of amoxicillin and clavulanic acid evaluated by population pharmacokinetics and Monte Carlo simulation

Amoxicillin (amoxicilline)-clavulanic acid has promising activity against pathogens that cause bone infections. We present the first evaluation of the bone penetration of a beta-lactam by population pharmacokinetics and pharmacodynamic profiling via Monte Carlo simulations. Twenty uninfected patients undergoing total hip replacement received a single intravenous infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid before surgery. Blood and bone specimens were collected. Bone samples were pulverized under liquid nitrogen with a cryogenic mill, including an internal standard. The drug concentrations in serum and total bone were analyzed by liquid chromatography-tandem mass spectrometry. We used NONMEM and S-ADAPT for population pharmacokinetic analysis and a target time of the non-protein-bound drug concentration above the MIC for > or = 50% of the dosing interval for near-maximal bactericidal activity in serum. The median of the ratio of the area under the curve (AUC) for bone/AUC for serum was 20% (10th to 90th percentile for between-subject variability [variability], 16 to 25%) in cortical bone and 18% (variability, 11 to 29%) in cancellous bone for amoxicillin and 15% (variability, 11 to 21%) in cortical bone and 10% (variability, 5.1 to 21%) in cancellous bone for clavulanic acid. Analysis in S-ADAPT yielded similar results. The equilibration half-lives between serum and bone were 12 min for amoxicillin and 14 min for clavulanic acid. For a 30-min infusion of 2,000 mg/200 mg amoxicillin-clavulanic acid every 4 h, amoxicillin achieved robust (> or = 90%) probabilities of target attainment (PTAs) for MICs of < or = 12 mg/liter in serum and 2 to 3 mg/liter in bone and population PTAs above 95% against methicillin-susceptible Staphylococcus aureus in bone and serum. The AUC of amoxicillin-clavulanic acid was 5 to 10 times lower in bone than in serum, and amoxicillin-clavulanic acid achieved a rapid equilibrium and favorable population PTAs against pathogens commonly encountered in bone infections.

Voriconazole pharmacokinetic variability in cystic fibrosis lung transplant patients

BACKGROUND

Aspergillosis is a high-risk complication in cystic fibrosis (CF) lung transplant patients. Azole antifungal drugs inhibit CYP3A4, resulting in significant metabolic drug-drug interactions. Voriconazole (VRZ) was marketed without therapeutic drug monitoring (TDM) recommendations, consistent with favorable pharmacokinetics, but regular determinations of plasma VRZ concentration were introduced in our center to manage interactions with calcineurin inhibitors and to document the achievement of therapeutic levels.

METHODS

VRZ TDM data analysis for trough concentration (C0) and peak concentration (C2) was carried out, using validated liquid chromatography assay with ultraviolet detection, for 35 CF lung transplant patients (mean age 25 years, mean weight 47 kg, balanced sex ratio) since 2003. Therapeutic range (C0: 1.5 +/- 0.5 - C2 : 4.0 +/- 1.0 mg/L) was expressed relative to pivotal pharmacokinetic trial data.

RESULTS

The duration of VRZ treatment ranged from 9 days to 22 months. The recommended standard dose of VRZ (200 mg twice a day, following the loading dose) resulted in significant plasma concentrations (>0.5 mg/L) in 20% of CF lung transplant patients. Therapeutic concentrations were obtained using higher doses (average 570 +/- 160 mg/day, +43%, P<0.01). Despite adaptation, C0 remained <0.5 mg/L (11%), even when the drug was administered intravenously, highlighting the variability of VRZ pharmacokinetics, possibly enhanced by CYP2C19 polymorphism. The risk of inefficacy during periods of underdosage was overcome by treatment with antifungal drug combinations (caspofungin, n=10). The therapeutic index was limited by neurologic effects (14%) and hepatic abnormalities (30%). VRZ concentrations correlated significantly (P<0.01) with aspartate aminotransferase levels but not with bilirubin levels. VRZ acted as a metabolic inhibitor of tacrolimus (C0 to dose ratio 5.8 +/- 2.6, n=31/VRZ versus 1.7 +/- 0.9 alone, P<0.001). Large changes in azole concentration affected the magnitude of the drug-drug interactions and adjustment requirements.

CONCLUSIONS

TDM is required because VRZ levels are often undetectable in treated CF lung transplant patients, supporting the use of antifungal drug combinations until achievement of VRZ C0 at a steady state between 1 and 2 mg/L. Plasma VRZ concentrations should be determined for the quantitative, individualized management of drug-drug interactions in lung transplant patients, in particular immunosuppressant such as tacrolimus, considering VRZ to be both a target and an inhibitor of CYP3A4.

Clinical cure of ventilator-associated pneumonia treated with piperacillin/tazobactam administered by continuous or intermittent infusion

The standard mode of administration of piperacillin treatment is by intermittent infusion. However, continuous infusion may be advantageous as beta-lactam antibiotics exhibit time-dependent antibacterial activity. In previous studies, we found a higher rate of clinical cure of ventilator-associated pneumonia (VAP) by continuous infusion rather than intermittent infusion of meropenem and ceftazidime. Therefore, the objective of this historical cohort study was to establish the clinical efficacy of piperacillin/tazobactam (PIP/TAZ) administered by continuous and intermittent infusion in the treatment of VAP in patients without renal failure. Logistic regression analysis showed a higher probability of clinical cure of VAP by continuous compared with intermittent infusion when the microorganism responsible for VAP had a minimum inhibitory concentration (MIC) of 8 microg/mL [8/9 (88.9%) vs. 6/15 (40.0%); odds ratio (OR)=10.79, 95% confidence interval (CI) 1.01-588.24; P=0.049] or 16 microg/mL [7/8 (87.5%) vs. 1/6 (16.7%); OR=22.89, 95% CI 1.19-1880.78; P=0.03]. Thus, administration of PIP/TAZ by continuous infusion may be considered more effective than intermittent infusion for the treatment of VAP caused by Gram-negative bacteria when the MIC of the microorganism responsible for VAP is 8-16 microg/mL in patients without renal failure.