A mathematical model-based analysis of the time-kill kinetics of ceftazidime/avibactam against Pseudomonas aeruginosa.

Objectives: To characterize quantitatively the effect of avibactam in potentiating ceftazidime against MDR Pseudomonas aeruginosa by developing a mathematical model to describe the bacterial response to constant concentration time-kill information and validating it using both constant and time-varying concentration-effect data from in vitro and in vivo infection systems. Methods: The time course of the bacterial population dynamics in the presence of static concentrations of ceftazidime and avibactam was modelled using a two-state pharmacokinetic/pharmacodynamic (PK/PD) model, consisting of active and resting states, to account for bactericidal activities, bacteria-mediated ceftazidime degradation and inhibition of degradation by avibactam. Ceftazidime's effect on the bacterial population was described as an enhancement of the death rate of the active population, with the effect of avibactam being to increase ceftazidime potency. Model validation was performed by comparing simulated time courses of bacterial responses with those from in vitro and in vivo experimental exposures of ceftazidime and avibactam that represented those predicted in an average patient dosed with 2 g/0.5 g ceftazidime/avibactam administered every 8 h as 2 h infusions. Results: The two-state model successfully described the bacterial population dynamics, ceftazidime degradation and its inhibition by avibactam. For external validation, the model correctly predicted the bacterial response of P. aeruginosa isolates evaluated in in vitro hollow-fibre and in vivo neutropenic mouse thigh and lung infection models. Conclusions: The PK/PD model and modelled strains successfully replicated the spread in activity when compared with a large selection of P. aeruginosa strains reported in the literature.

Potentiation of ceftazidime by avibactam against ß-lactam-resistant Pseudomonas aeruginosa in an in vitro infection model.

Objectives: This study evaluated the in vitro pharmacodynamics of combinations of ceftazidime and the non-ß-lactam ß-lactamase inhibitor, avibactam, against ceftazidime-, piperacillin/tazobactam- and meropenem-multiresistant Pseudomonas aeruginosa by a quantitative time-kill method. Methods: MICs of ceftazidime plus 0-16 mg/L avibactam were determined against eight isolates of P. aeruginosa . Single-compartment, 24 h time-kill kinetics were investigated for three isolates at 0-16 mg/L avibactam with ceftazidime at 0.25-4-fold the MIC as measured at the respective avibactam concentration. Ceftazidime and avibactam concentrations were measured by LC-MS/MS during the time-kill kinetic studies to evaluate drug degradation. Results: Avibactam alone displayed no antimicrobial activity. MICs of ceftazidime decreased by 8-16-fold in the presence of avibactam at 4 mg/L. The changes in log 10 cfu/mL at both the 10 h and 24 h timepoints (versus 0 h) revealed bacterial killing at ≥1-fold MIC. Significantly higher concentrations of ceftazidime alone, as compared with those of ceftazidime in combination, were required to produce any given kill. Without avibactam, ceftazidime degradation was significant (defined as degradation t 1/2 < 24 h), with as little as 19% ± 18% of the original concentration remaining at 8 h for the most resistant strain. In combination with avibactam, ceftazidime degradation at ≥ 1-fold MIC was negligible. Conclusion: The addition of avibactam protected ceftazidime from degradation in a dose-dependent manner and restored its cidal and static activity at concentrations in combination well below the MIC of ceftazidime alone.

Translating slow-binding inhibition kinetics into cellular and in vivo effects.

Many drug candidates fail in clinical trials owing to a lack of efficacy from limited target engagement or an insufficient therapeutic index. Minimizing off-target effects while retaining the desired pharmacodynamic (PD) response can be achieved by reduced exposure for drugs that display kinetic selectivity in which the drug-target complex has a longer half-life than off-target-drug complexes. However, though slow-binding inhibition kinetics are a key feature of many marketed drugs, prospective tools that integrate drug-target residence time into predictions of drug efficacy are lacking, hindering the integration of drug-target kinetics into the drug discovery cascade. Here we describe a mechanistic PD model that includes drug-target kinetic parameters, including the on- and off-rates for the formation and breakdown of the drug-target complex. We demonstrate the utility of this model by using it to predict dose response curves for inhibitors of the LpxC enzyme from Pseudomonas aeruginosa in an animal model of infection.

Pharmacodynamics of Ceftazidime and Avibactam in Neutropenic Mice with Thigh or Lung Infection.

Avibactam is a new non-ß-lactam ß-lactamase inhibitor that shows promising restoration of ceftazidime activity against microorganisms producing Ambler class A extended-spectrum ß-lactamases (ESBLs) and carbapenemases such as KPCs, class C ß-lactamases (AmpC), and some class D enzymes. To determine optimal dosing combinations of ceftazidime-avibactam for treating infections with ceftazidime-resistant Pseudomonas aeruginosa, pharmacodynamic responses were explored in murine neutropenic thigh and lung infection models. Exposure-response relationships for ceftazidime monotherapy were determined first. Subsequently, the efficacy of adding avibactam every 2 h (q2h) or q8h to a fixed q2h dose of ceftazidime was determined in lung infection for two strains. Dosing avibactam q2h was significantly more efficacious, reducing the avibactam daily dose for static effect by factors of 2.7 and 10.1, whereas the mean percentage of the dosing interval that free drug concentrations remain above the threshold concentration of 1 mg/liter (%fT>C(T) 1 mg/liter) yielding bacteriostasis was similar for both regimens, with mean values of 21.6 (q2h) and 18.5 (q8h). Dose fractionation studies of avibactam in both the thigh and lung models indicated that the effect of avibactam correlated well with %fT>C(T) 1 mg/liter. This parameter of avibactam was further explored for four P. aeruginosa strains in the lung model and six in the thigh model. Parameter estimates of %fT>C(T) 1 mg/liter for avibactam ranged from 0 to 21.4% in the lung model and from 14.1 to 62.5% in the thigh model to achieve stasis. In conclusion, addition of avibactam enhanced the effect of ceftazidime, which was more pronounced at frequent dosing and well related with %fT>C(T) 1 mg/liter. The thigh model appeared more stringent, with higher values, ranging up to 62.5% fT>C(T) 1 mg/liter, required for a static effect.

In vitro pharmacokinetics/pharmacodynamics of the combination of avibactam and aztreonam against MDR organisms.

OBJECTIVES: The combination of aztreonam and avibactam has been proposed for the treatment of infections caused by metallo-ß-lactamase-producing Gram-negative organisms, given the stability of aztreonam against metallo-ß-lactamases plus the broad coverage of avibactam against AmpC ß-lactamases and ESBLs. This study aimed to evaluate the efficacy of the combination against four clinical isolates with defined but diverse ß-lactamase profiles. METHODS: The MICs of aztreonam were determined without and with avibactam (1, 2, 4, 8 and 16 mg/L). Using the MIC values, the static time-kill kinetic studies were designed to encompass aztreonam concentrations of 0.25, 0.5, 1, 2 and 4 times the MIC at the respective avibactam concentrations from 0 to 8 mg/L. Aztreonam and avibactam concentrations were determined by LC-MS/MS during the course of the time-kill kinetic studies to evaluate whether avibactam protects aztreonam from degradation. RESULTS: Three of the four isolates had aztreonam MICs ≥128 mg/L in monotherapy. Dramatically increasing susceptibility associated with a decrease in aztreonam MIC was observed with increasing avibactam concentration. Against all isolates, the combinations resulted in greater killing with a much lower dose requirement for aztreonam. The resulting changes in base-10 logarithm of cfu/mL at both the 10 h and 24 h references (versus 0 h) were synergistic. In contrast, a significantly higher concentration of aztreonam in the monotherapy was required to produce the same kill as that in the combination therapy, due to rapid aztreonam degradation in two isolates. CONCLUSIONS: The aztreonam/avibactam combination protects aztreonam from hydrolysis and provides synergy in antimicrobial activity against multiple ß-lactamase-expressing strains with a wide MIC range.

Translational Population-Pharmacodynamic Modeling of a Novel Long-Acting siRNA Therapy, Inclisiran, for the Treatment of Hypercholesterolemia.

Inclisiran is a novel N-acetylgalactosamine (GalNAc) conjugated small-interfering ribonucleic acid (siRNA) therapy designed to specifically target proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA in the liver for the treatment of hypercholesterolemia. Inclisiran's GalNAc attachment results in a rapid uptake into the liver, and thus a short plasma half-life, but long duration of effects on PCSK9 inhibition and low-density lipoprotein cholesterol (LDL-C) lowering. The effects on PCSK9 inhibition and consequent LDL-C reduction are sustained for more than 6 months following a single subcutaneous (s.c.) dose, despite inclisiran being detectable in the plasma only for up to 48 hours. A kinetic-pharmacodynamic (K-PD) model was developed to characterize inclisiran's dose-related LDL-C lowering effects and to evaluate the impact of intrinsic and extrinsic factors on LDL-C lowering. To accommodate the long duration of action, the K-PD model incorporated an effect compartment which represents the liver. Inclisiran concentration in the liver leads to decreased production of the PCSK9 protein and allow recycling of more LDL-C receptors on the hepatocyte cell surface, which results in a reduction of circulating LDL-C. The analysis of covariates identified PCSK9 and LDL-C baseline levels as important factors for the effects of LDL-C lowering. Observations and modeling and simulation results demonstrated that PCSK9 and LDL-C reductions are achieved rapidly after dosing and sustained when patients are treated with a 300 mg s.c. dose once every 6 months.

Comparative in vitro and in vivo efficacies of human simulated doses of ceftazidime and ceftazidime-avibactam against Pseudomonas aeruginosa.

The combination of ceftazidime and avibactam possesses potent activity against resistant Gram-negative pathogens, including Pseudomonas aeruginosa. We compared the efficacies of human simulated doses of ceftazidime and ceftazidime-avibactam using a hollow-fiber system and neutropenic and immunocompetent murine thigh infection models. Twenty-seven clinical P. aeruginosa isolates with ceftazidime MICs of 8 to 128 mg/liter and ceftazidime-avibactam MICs of 4 to 32 mg/liter were utilized in neutropenic mouse studies; 15 of the isolates were also evaluated in immunocompetent mice. Six isolates were studied in both the hollow-fiber system and the neutropenic mouse. In both systems, the free drug concentration-time profile seen in humans given 2 g of ceftazidime every 8 h (2-h infusion), with or without avibactam at 500 mg every 8 h (2-h infusion), was evaluated. In vivo activity was pharmacodynamically predictable based on the MIC. Ceftazidime decreased bacterial densities by ≥0.5 log unit for 10/27 isolates, while ceftazidime-avibactam did so for 22/27 isolates. In immunocompetent animals, enhancements in activity were seen for both drugs, with ceftazidime achieving reductions of ≥0.3 log unit for 10/15 isolates, whereas ceftazidime-avibactam did so against all 15 isolates. In vitro, ceftazidime resulted in regrowth by 24 h against all isolates, while ceftazidime-avibactam achieved stasis or better against 4/7 isolates. Mutants with elevated ceftazidime-avibactam MICs appeared after 24 h from 3/7 isolates studied in vitro; however, no resistant mutants were detected in vivo. Against this highly ceftazidime-nonsusceptible population of P. aeruginosa, treatment with human simulated doses of ceftazidime-avibactam resulted in pharmacodynamically predictable activity, particularly in vivo, against isolates with MICs of ≤16 mg/liter, and this represents a potential new option to combat these difficult-to-treat pathogens.

Responding to the challenge of untreatable gonorrhea: ETX0914, a first-in-class agent with a distinct mechanism-of-action against bacterial Type II topoisomerases.

With the diminishing effectiveness of current antibacterial therapies, it is critically important to discover agents that operate by a mechanism that circumvents existing resistance. ETX0914, the first of a new class of antibacterial agent targeted for the treatment of gonorrhea, operates by a novel mode-of-inhibition against bacterial type II topoisomerases. Incorporating an oxazolidinone on the scaffold mitigated toxicological issues often seen with topoisomerase inhibitors. Organisms resistant to other topoisomerase inhibitors were not cross-resistant with ETX0914 nor were spontaneous resistant mutants to ETX0914 cross-resistant with other topoisomerase inhibitor classes, including the widely used fluoroquinolone class. Preclinical evaluation of ETX0914 pharmacokinetics and pharmacodynamics showed distribution into vascular tissues and efficacy in a murine Staphylococcus aureus infection model that served as a surrogate for predicting efficacious exposures for the treatment of Neisseria gonorrhoeae infections. A wide safety margin to the efficacious exposure in toxicological evaluations supported progression to Phase 1. Dosing ETX0914 in human volunteers showed sufficient exposure and minimal adverse effects to expect a highly efficacious anti-gonorrhea therapy.

In vitro microdialysis sampling of docetaxel.

Microdialysis is a technique that allows sampling compounds from the extracellular fluid in different tissues, such as muscle, lung, and brain. However, the feasibility of using this technique with lipopohilic and high molecular weight compounds has been questioned, since these compounds are less likely to diffuse through the dialysis membrane. Therefore, it was the objective of this study to investigate the feasibility of doing microdialysis of docetaxel by determining its recovery by the microdialysis probe. Three different methods were investigated: extraction efficiency, retrodialysis, and no-net-flux. For the first two methods, three different concentrations were tested: 2.5, 5, and 9 mg/l. The recovery obtained for each concentration was 49.3 +/- 6.7 (n = 4), 44.6 +/- 5.4 (n = 3), and 34.7 +/- 2.1 (n = 4) by extraction efficiency, and 53.4 +/- 7.9 (n = 3), 61.4 +/- 7.6 (n = 3), and 64.2 +/- 1.9 (n = 3) by retrodialysis, respectively. The average recovery obtained by no-net-flux was 68.7 +/- 9.6 (n = 5). Although it has been reported that microdialysis cannot be applied to lipophilic compounds, the results here show the opposite. The high recoveries obtained for docetaxel in all methods applied show that the compound can diffuse through the probe membrane. Overall, docetaxel seems to be very suitable for microdialysis despite its lipophilicity and high molecular weight.

Novel DNA gyrase inhibiting spiropyrimidinetriones with a benzisoxazole scaffold: SAR and in vivo characterization.

The compounds described herein with a spirocyclic architecture fused to a benzisoxazole ring represent a new class of antibacterial agents that operate by inhibition of DNA gyrase as corroborated in an enzyme assay and by the inhibition of precursor thymidine into DNA during cell growth. Activity resided in the configurationally lowest energy (2S,4R,4aR) diastereomer. Highly active compounds against Staphylococcus aureus had sufficiently high solubility, high plasma protein free fraction, and favorable pharmacokinetics to suggest that in vivo efficacy could be demonstrated, which was realized with compound (-)-1 in S. aureus mouse infection models. A high drug exposure NOEL on oral dosing in the rat suggested that a high therapeutic margin could be achieved. Importantly, (-)-1 was not cross-resistant with other DNA gyrase inhibitors such as fluoroquinolone and aminocoumarin antibacterials. Hence, this class shows considerable promise for the treatment of infections caused by multidrug resistant bacteria, including S. aureus.

Model-based drug discovery: implementation and impact.

Model-based drug discovery (MBDDx) aims to build and continuously improve the quantitative understanding of the relation between drug exposure (target engagement) efficacy and safety, to support target validation; to define compound property criteria for lead optimization and safety margins; to set the starting dose; and to predict human dose and scheduling for clinical candidates alone, or in combination with other medicines. AstraZeneca has systematically implemented MBDDx within all drug discovery programs, with a focused investment to build a preclinical modeling and simulation capability and an in vivo information platform and architecture, the implementation, impact and learning of which are discussed here.

Avaliação da atividade antimicrobiana de Cymbopogon citratus / Evaluation of the antimicrobial activity of Cymbopogon citratus

Cymbopogon citratus (DC) Stapf. é uma gramínea, conhecida popularmente como capim-cidró, capim-cheiroso, erva-cidreira, entre outros, e, em inglês, "lemon grass". A população utiliza o chá ou abafado, preparado a partir de suas folhas, como calmante, digestivo, estomáquico, em dores de cabeça, antiespasmódico, entre outras aplicações. Devido às propriedades antimicrobianas apresentadas pelo óleo volátil de capim-cidró, este trabalho tem por objetivo avaliar a atividade antibacteriana e antifúngica do óleo volátil, extratos aquosos e hidroetanólico, obtidos a partir das folhas frescas e secas da planta. A atividade antimicrobiana foi avaliada pelo método de difusão em ágar, frente aos microrganismos...