Pharmacodynamic Attainment of the Synergism of Meropenem and Fosfomycin Combination against Pseudomonas aeruginosa Producing Metallo-ß-Lactamase.

Fosfomycin combined with other antimicrobials has shown good efficacy against multidrug-resistant (MDR) bacteria in both in vitro and clinical studies; however, the activity of fosfomycin combined with other antimicrobials against metallo-ß-lactamase (MBL)-producing Pseudomonas aeruginosa strains has not been tested. The objective of this study was to determine the synergism and optimal intravenous dosing regimens of fosfomycin with meropenem against MDR and MBL-producing P. aeruginosa strains. The MICs of both antimicrobials were determined by the checkerboard method and analyzed by two synergism tests with 19 clones of P. aeruginosa isolates, 10 of which were MBL producers. A pharmacodynamic (PD) analysis was performed for meropenem (administered at 1 g every 8 h [q8h], 1.5 g every 6 h [q6h], and 2 g q8h) and fosfomycin (administered at 4 g q8h, 4 g q6h, 6 g q8h, and 8 g q8h) regimens with a dose reduction for renal impairment by determining the probability of target attainment (PTA) for target PD indices of meropenem (the percentage of the time in a 24-h duration at which the free drug concentration remains above the MIC [fT>MIC], ≥40%) and fosfomycin (the ratio of the area under the free drug concentration-versus-time curve over 24 h and the MIC [fAUC/MIC], ≥40.8). The combination reduced the MIC50 and MIC90 by 8-fold. Seven (44%) isolates with MICs in the intermediate or resistant ranges became sensitive to meropenem. For the MBL-producing isolates, the combination resulted in 40% of isolates becoming sensitive to meropenem. The meropenem regimens reached a PTA of ≥90% (MIC = 4 µg/ml) in 6 (32%) isolates when they were used as monotherapy and 13 (68%) isolates when they were combined with fosfomycin. None of the fosfomycin monotherapy regimens reached the PTA of ≥90% (MIC = 16 µg/ml). When combined with meropenem, the fosfomycin regimens reached the PTA of ≥90% in 14 (74%) isolates. The increase in pharmacodynamic activities resulting from the synergistic action of meropenem with fosfomycin demonstrates the potential relevance of this combination to fight infections caused by MDR and MBL-producing P. aeruginosa strains.

Projected 24-hour post-dose ocular itching scores post-treatment with olopatadine 0.7% versus 0.2.

Olopatadine is an antihistamine and mast cell stabilizer used for treating allergic conjunctivitis. Olopatadine 0.7% has been recently approved for daily dosing in the US, which supersedes the previously approved 0.2% strength. The objective of this analysis was to characterize patients who have better itching relief at 24 h when taking olopatadine 0.7% treatment instead of olopatadine 0.2% (in terms of proportions of responses) and relate this to the severity of baseline itching as an indirect metric of a patient's sensitivity to antihistamines. A differential odds model was developed using data from two conjunctival allergen challenge (CAC) studies to characterize individual-level and population-level response to ocular itching following olopatadine treatment and the data was analyzed retrospectively. This modeling analysis was designed to predict 24 h ocular itching scores and to quantify the differences in 24 h itching relief following treatment with olopatadine 0.2% versus 0.7% in patients with moderate-to-high baseline itching. A one-compartment kinetic-pharmacodynamic Emax model was used to determine the effect of olopatadine. Impact of baseline itching severity, vehicle effect and the drug effect on the overall itching scores post-treatment were explicitly incorporated in the model. The model quantified trends observed in the clinical data with regards to both mean scores and the proportions of patients responding to olopatadine treatment. The model predicts a higher proportion of patients in the olopatadine 0.7% versus 0.2% group will experience relief within 24 h. This prediction was confirmed with retrospective clinical data analysis. The number of allergy patients relieved with olopatadine 0.7% increased with higher baseline itching severity scores, when compared to olopatadine 0.2%.

Ranibizumab Population Pharmacokinetics and Free VEGF Pharmacodynamics in Preterm Infants With Retinopathy of Prematurity in the RAINBOW Trial.

Purpose: To develop a population pharmacokinetic (PK) model for intravitreal ranibizumab in infants with retinopathy of prematurity (ROP) and assess plasma free vascular endothelial growth factor (VEGF) pharmacodynamics (PD). Methods: The RAnibizumab compared with laser therapy for the treatment of INfants BOrn prematurely With retinopathy of prematurity (RAINBOW) trial enrolled 225 infants to receive a bilateral intravitreal injection of ranibizumab 0.1 mg, ranibizumab 0.2 mg, or laser in a 1:1:1 ratio and included sparse sampling of blood for population PK and PD analysis. An adult PK model using infant body weight as a fixed allometric covariate was re-estimated using the ranibizumab concentrations in the preterm population. Different variability, assumptions, and covariate relationships were explored. Model-based individual predicted concentrations of ranibizumab were plotted against observed free VEGF concentrations. Results: Elimination of ranibizumab had a median half-life of 5.6 days from the eye and 0.3 days from serum, resulting in an apparent serum half-life of 5.6 days. Time to reach maximum concentration was rapid (median: 1.3 days). Maximum concentration (median 24.3 ng/mL with ranibizumab 0.2 mg) was higher than that reported in adults. No differences in plasma free VEGF concentrations were apparent between the groups or over time. Plotted individual predicted concentrations of ranibizumab against observed free VEGF concentrations showed no relationship. Conclusions: In preterm infants with ROP, elimination of ranibizumab from the eye was the rate-limiting step and was faster compared with adults. No reduction in plasma free VEGF was observed. The five-year clinical safety follow-up from RAINBOW is ongoing. Translational Relevance: Our population PK and VEGF PD findings suggest a favorable ocular efficacy: systemic safety profile for ranibizumab in preterm infants.

Nonlinear Mixed-Effects Model Development and Simulation Using nlmixr and Related R Open-Source Packages.

nlmixr is a free and open-source R package for fitting nonlinear pharmacokinetic (PK), pharmacodynamic (PD), joint PK-PD, and quantitative systems pharmacology mixed-effects models. Currently, nlmixr is capable of fitting both traditional compartmental PK models as well as more complex models implemented using ordinary differential equations. We believe that, over time, it will become a capable, credible alternative to commercial software tools, such as NONMEM, Monolix, and Phoenix NLME.

Performance of the SAEM and FOCEI Algorithms in the Open-Source, Nonlinear Mixed Effect Modeling Tool nlmixr.

The free and open-source package nlmixr implements pharmacometric nonlinear mixed effects model parameter estimation in R. It provides a uniform language to define pharmacometric models using ordinary differential equations. Performances of the stochastic approximation expectation-maximization (SAEM) and first order-conditional estimation with interaction (FOCEI) algorithms in nlmixr were compared with those found in the industry standards, Monolix and NONMEM, using the following two scenarios: a simple model fit to 500 sparsely sampled data sets and a range of more complex compartmental models with linear and nonlinear clearance fit to data sets with rich sampling. Estimation results obtained from nlmixr for FOCEI and SAEM matched the corresponding output from NONMEM/FOCEI and Monolix/SAEM closely both in terms of parameter estimates and associated standard errors. These results indicate that nlmixr may provide a viable alternative to existing tools for pharmacometric parameter estimation.

Flexible interaction model for complex interactions of multiple anesthetics.

BACKGROUND: Minto et al. (Anesthesiology 2000) described a mathematical approach based on response surface methods for characterizing drug-drug interactions between several intravenous anesthetic drugs. To extend this effort, the authors developed a flexible interaction model based on the general Hill dose-response relation that includes a set of parameters that can be statistically assessed for interaction significance. METHODS: This new model was developed to identify pharmacologically meaningful interaction-related parameters and address mathematical limitations in previous models. The flexible interaction model and the model of Minto et al. were compared in their assessment of additivity using simulated sample data sets. The flexible interaction model was also compared with the Minto model in describing drug interactions using data from several other clinical studies of propofol, opioids, and benzodiazepines from Short et al. (Anesthesiology 2002) and Kern et al. (Anesthesiology 2004). RESULTS: The flexible interaction model was able to accurately classify an additive interaction based on the classic definition proposed by Loewe, with at most an 8% difference between the two surfaces. Also, the proposed model fit the clinical interaction data as well or slightly better than that of Minto et al. CONCLUSIONS: The new model can accurately classify additive and synergistic drug interactions. It also can classify antagonistic interactions with biologically rational surfaces. This has been a problem for other interaction models in the past. The statistically assessable interaction parameters provide a quantitative manner to assess the interaction significance.

Effect of initial subcellular localization of progesterone receptor on import kinetics and transcriptional activity.

Progesterone receptors (PR) are ligand-activated transcription factors that modulate transcription by activating genes. There are two isoforms of PR, PRA and PRB. In most cell contexts, the PRA isoform is a repressor of the PRB isoform. Without hormone induction, PRA is mostly located in the nucleus whereas PRB distributes both in the nucleus and in the cytoplasm. In this paper, a new model system has been used to study the impact of initial subcellular localization, and import rate of progesterone receptor on transcriptional activity. This new model system involves using a mutant version of PRB which is found only in the cytoplasmic compartment of cells in the unliganded state, making the distribution of the receptor more homogeneous to start with compared with the previous model, wild type (wt) PRB, which has a more heterogeneous distribution (nuclear and cytoplasmic even without ligand). Import kinetics has been shown to be one of the major means by which to regulate PR transcriptional activity. Fluorescence microscopy was used to measure green fluorescent protein tagged PRB import rate into the nucleus. Luciferase reporter gene assay was used to measure transcriptional activity of PRB. In addition, a two-hybrid assay was performed to measure the interaction between PRB and importin alpha. Mutant versions of PRA and PRB with the constitutively active nuclear localization signal removed were created (PRA-NLSc mutant and PRB-NLSc mutant). These PR mutants were found to localize mainly in the cytoplasm in the absence of hormone. With addition of hormone, PR mutants translocated to the nucleus, although at a slower rate compared to wt PRB. Our results show that the activation of reporter gene transcription is proportional to the nuclear import rate of PRB-NLSc mutant, and the difference in import kinetics between wt PRB and the PRB-NLSc mutant is due to a stronger interaction of wt PRB with importin alpha. We also show that the hormone inducible NLS in PR, NLSh, is a weak nuclear localization signal even without hormone and can act as a weak hormone dependent nuclear localization signal when combined with the ligand binding domain of PR. In addition, by changing the initial subcellular localization of PRA from the nucleus to the cytoplasm, this diminished PRA's ability to act as an inhibitor of PRB.