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 beta -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 beta -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

Population pharmacokinetics at two dose levels and pharmacodynamic profiling of flucloxacillin

Flucloxacillin is often used for the treatment of serious infections due to sensitive staphylococci. The pharmacokinetic (PK)-pharmacodynamic (PD) breakpoint of flucloxacillin has not been determined by the use of population PK. Targets based on the duration of non-protein-bound concentrations above the MIC (fT(> MIC)) best correlate with clinical cure rates for beta-lactams. We compared the breakpoints for flucloxacillin between several dosage regimens. In a randomized, two-way crossover study, 10 healthy volunteers received 500 mg and 1,000 mg flucloxacillin as 5-min intravenous infusions. Drug concentrations were determined by high-pressure liquid chromatography. We used the programs WinNonlin for noncompartmental analysis and statistics and NONMEM for population PK and Monte Carlo simulation. We compared the probability of target attainment (PTA) for intermittent- and continuous-dosage regimens based on the targets of fT(> MIS)s of >= 50% and >= 30% of the dosing interval. The clearance and the volume of distribution were very similar after the administration of 500 mg and 1,000 mg flucloxacillin. We estimated renal and nonrenal clearances of 5.37 liters/h (coefficient of variation, 19%) and 2.73 liters/h (33%). For near maximal killing (target, fT(> MIC) of >= 50%) flucloxacillin showed a robust (>= 90%) PTA up to MICs of 0.75 to 1 mg/liter (PTA of 860/v at 1 mg/liter) for a continuous or a prolonged infusion of 6 g/day. Short-term infusions of 6 g/day had a lower breakpoint of 0.25 to 0.375 mg/liter. The flucloxacillin PK was linear for doses of 500 mg and 1,000 mg. Prolonged and continuous infusion at a 66% lower daily dose achieved the same PK-PD breakpoints as short-term infusions. Prolonged infusion and continuous infusion are appealing options for the treatment of serious infections caused by sensitive staphylococci

High-intensity meropenem combinations with polymyxin B: new strategies to overcome carbapenem resistance in Acinetobacter baumannii

The pharmacodynamics of polymyxin/carbapenem combinations against carbapenem-resistant Acinetobacter baumannii (CRAB) are largely unknown. Our objective was to determine whether intensified meropenem regimens in combination with polymyxin B enhance killing and resistance suppression of CRAB

Substantial impact of altered pharmacokinetics in critically Ill patients on the antibacterial effects of meropenem evaluated via the dynamic hollow-fiber infection model

Critically ill patients frequently have substantially altered pharmacokinetics compared to non-critically ill patients. We investigated the impact of pharma-cokinetic alterations on bacterial killing and resistance for commonly used meropenem dosing regimens. A Pseudomonas aeruginosa isolate (MICmeropenem 0.25 mg/liter) was studied in the hollow-fiber infection model (inoculum similar to 10(7.5) CFU/ml; 10 days). Pharmacokinetic profiles representing critically ill patients with augmented renal clearance (ARC), normal, or impaired renal function (creatinine clearances of 285, 120, or similar to 10 ml/min, respectively) were generated for three meropenem regimens (2, 1, and 0.5 g administered as 8-hourly 30-min infusions), plus 1 g given 12 hourly with impaired renal function. The time course of total and less-susceptible populations and MICs were determined. Mechanism-based modeling (MBM) was performed using S-ADAPT. All dosing regimens across all renal functions produced similar initial bacterial killing (5 x MIC) = 56 and 69%, fC(min)/MIC = 32-fold increases in MIC) accompanied all regrowth. Bacterial counts remained suppressed across 10 days with normal (2-g 8-hourly regimen) and impaired (all regimens) renal function (fT >5 x MIC >= 82%, fC(min)/MIC >= 2). The MBM successfully described bacterial killing and regrowth for all renal functions and regimens simultaneously. Optimized dosing regimens, including extended infusions and/or combinations, supported by MBM and Monte Carlo simulations, should be evaluated in the context of ARC to maximize bacterial killing and suppress resistance emergence

Optimization and evaluation of piperacillin plus tobramycin combination dosage regimens againstfor patients with altered pharmacokineticsthe hollow-fiber infection model and mechanism-based modeling

Augmented renal clearance (ARC) in critically-ill patients can result in suboptimal drug exposures and treatment failure. Combination dosage regimens accounting for ARC have never been optimized and evaluated againstusing the hollow-fiber infection model (HFIM). Using aisolate from a critically-ill patient and static concentration time-kill experiments (SCTK), we studied clinically relevant piperacillin and tobramycin concentrations, alone and in combinations, at two inocula (10and 10CFU/mL) over 72h. We subsequently evaluated the effect of optimized piperacillin (4 g q4h, 0.5h infusion) plus tobramycin (5 mg/kg q24h, 7 mg/kg q24h and 10 mg/kg q48h as 0.5h infusions) regimens on killing and regrowth in the HFIM, simulating a creatinine clearance of 250 mL/min. Mechanism-based modeling was performed in S-ADAPT. In SCTKs, piperacillin plus tobramycin (except combinations with 8 mg/liter tobramycin at low inoculum) achieved synergistic killing (≥2 logthe most active monotherapy at 48h and 72h) and prevented regrowth. Piperacillin monotherapy (4 g q4h) in the HFIM provided 2.4 loginitial killing followed by regrowth at 24h with resistance emergence. Tobramycin monotherapies displayed rapid initial killing (≥5 logat 13h) followed by extensive regrowth. As predicted by mechanism-based modeling, the piperacillin plus tobramycin dosage regimens were synergistic and provided ≥5 logkilling with resistance suppression over 8 days in the HFIM. Optimized piperacillin plus tobramycin regimens provided significant bacterial killing and suppressed resistance emergence. These regimens appear highly promising for effective and early treatment, even in the near-worst case scenario of ARC

The combination of colistin and doripenem is synergistic against Klebsiella pneumoniae at multiple inocula and suppresses colistin resistance in an in vitro pharmacokinetic/pharmacodynamic model

There has been a resurgence of interest in aerosolization of antibiotics for treatment of patients with severe pneumonia caused by multidrug-resistant pathogens. A combination formulation of amikacin-fosfomycin is currently undergoing clinical testing although the exposure-response relationships of these drugs have not been fully characterized. The aim of this study was to describe the individual and combined antibacterial effects of simulated epithelial lining fluid exposures of aerosolized amikacin and fosfomycin against resistant clinical isolates of Pseudomonas aeruginosa (MICs of 16 mg/liter and 64 mg/liter) and Klebsiella pneumoniae (MICs of 2 mg/liter and 64 mg/liter) using a dynamic hollow-fiber infection model over 7 days. Targeted peak concentrations of 300 mg/liter amikacin and/or 1,200 mg/liter fosfomycin as a 12-hourly dosing regimens were used. Quantitative cultures were performed to describe changes in concentrations of the total and resistant bacterial populations. The targeted starting inoculum was 10(8) CFU/ml for both strains. We observed that neither amikacin nor fosfomycin monotherapy was bactericidal against P. aeruginosa while both were associated with rapid amplification of resistant P. aeruginosa strains (about 10(8) to 10(9) CFU/ml within 24 to 48 h). For K. pneumoniae, amikacin but not fosfomycin was bactericidal. When both drugs were combined, a rapid killing was observed for P. aeruginosa and K. pneumoniae (6-log kill within 24 h). Furthermore, the combination of amikacin and fosfomycin effectively suppressed growth of resistant strains of P. aeruginosa and K. pneumoniae In conclusion, the combination of amikacin and fosfomycin was effective at maximizing bacterial killing and suppressing emergence of resistance against these clinical isolates

Pharmacodynamic Modeling of Anti-Cancer Activity of Tetraiodothyroacetic Acid in a Perfused Cell Culture System

Unmodified or as a poly[lactide-co-glycolide] nanoparticle, tetraiodothyroacetic acid (tetrac) acts at the integrin αvβ3 receptor on human cancer cells to inhibit tumor cell proliferation and xenograft growth. To study in vitro the pharmacodynamics of tetrac formulations in the absence of and in conjunction with other chemotherapeutic agents, we developed a perfusion bellows cell culture system. Cells were grown on polymer flakes and exposed to various concentrations of tetrac, nano-tetrac, resveratrol, cetuximab, or a combination for up to 18 days. Cells were harvested and counted every one or two days. Both NONMEM VI and the exact Monte Carlo parametric expectation maximization algorithm in S-ADAPT were utilized for mathematical modeling. Unmodified tetrac inhibited the proliferation of cancer cells and did so with differing potency in different cell lines. The developed mechanism-based model included two effects of tetrac on different parts of the cell cycle which could be distinguished. For human breast cancer cells, modeling suggested a higher sensitivity (lower IC50) to the effect on success rate of replication than the effect on rate of growth, whereas the capacity (Imax) was larger for the effect on growth rate. Nanoparticulate tetrac (nano-tetrac), which does not enter into cells, had a higher potency and a larger anti-proliferative effect than unmodified tetrac. Fluorescence-activated cell sorting analysis of harvested cells revealed tetrac and nano-tetrac induced concentration-dependent apoptosis that was correlated with expression of pro-apoptotic proteins, such as p53, p21, PIG3 and BAD for nano-tetrac, while unmodified tetrac showed a different profile. Approximately additive anti-proliferative effects were found for the combinations of tetrac and resveratrol, tetrac and cetuximab (Erbitux), and nano-tetrac and cetuximab. Our in vitro perfusion cancer cell system together with mathematical modeling successfully described the anti-proliferative effects over time of tetrac and nano-tetrac and may be useful for dose-finding and studying the pharmacodynamics of other chemotherapeutic agents or their combinations

Elucidation of the Mode of Action of a New Antibacterial Compound Active against Staphylococcus aureus and Pseudomonas aeruginosa.

Nosocomial and community-acquired infections caused by multidrug resistant bacteria represent a major human health problem. Thus, there is an urgent need for the development of antibiotics with new modes of action. In this study, we investigated the antibacterial characteristics and mode of action of a new antimicrobial compound, SPI031 (N-alkylated 3, 6-dihalogenocarbazol 1-(sec-butylamino)-3-(3,6-dichloro-9H-carbazol-9-yl)propan-2-ol), which was previously identified in our group. This compound exhibits broad-spectrum antibacterial activity, including activity against the human pathogens Staphylococcus aureus and Pseudomonas aeruginosa. We found that SPI031 has rapid bactericidal activity (7-log reduction within 30 min at 4x MIC) and that the frequency of resistance development against SPI031 is low. To elucidate the mode of action of SPI031, we performed a macromolecular synthesis assay, which showed that SPI031 causes non-specific inhibition of macromolecular biosynthesis pathways. Liposome leakage and membrane permeability studies revealed that SPI031 rapidly exerts membrane damage, which is likely the primary cause of its antibacterial activity. These findings were supported by a mutational analysis of SPI031-resistant mutants, a transcriptome analysis and the identification of transposon mutants with altered sensitivity to the compound. In conclusion, our results show that SPI031 exerts its antimicrobial activity by causing membrane damage, making it an interesting starting point for the development of new antibacterial therapies

Synthesis and structure-activity relationship of thioacetamide-triazoles against Escherichia coli

Infections due to Gram-negative bacteria are increasingly dangerous due to the spread of multi-drug resistant strains, emphasizing the urgent need for new antibiotics with alternative modes of action. We have previously identified a novel class of antibacterial agents, thioacetamide-triazoles, using an antifolate targeted screen and determined their mode of action which is dependent on activation by cysteine synthase A. Herein, we report a detailed examination of the anti