Impact of nutritional factors on in-vitro PK/PD modelling of polymyxin B against various strains of Acinetobacter baumannii

The main objective of this study was to assess the effect of rich artificial cation-adjusted Mueller-Hinton broth (CAMHB) on the growth of three strains of Acinetobacter baumannii (ATCC 19606 and two clinical strains), either susceptible or resistant to polymyxin B (PMB), and on PMB bactericidal activity. A pharmacokinetic (PK)/pharmacodynamic (PD) modelling approach was used to characterize the effect of PMB in various conditions. Time-kill experiments were performed using undiluted CAMHB or CAMHB diluted to 50%, 25% and 10%, with or without Ca2+ and Mg2+ compensation (known to affect PMB activity), and with PMB concentrations ranging from 0.25 to 256 mg/L based on the strain's MIC. For each strain, time-kill replicates were modelled using NONMEM. Unexpectedly, dilution of CAMHB by up to 10-fold did not affect the growth rate of any of the three strains in the absence of PMB. However, the bactericidal activity of PMB increased with medium dilution, resulting in a reduction in the apparent bacterial regrowth of the various strains observed after a few hours. Data for each strain were well characterized by a PK/PD model, with two bacterial subpopulations with different susceptibility to PMB (more susceptible and less susceptible). The impact of medium dilution and cation compensation showed relatively high, unexplained between-strain variability. Further studies are needed to characterize the mechanism underlying the medium dilution effect.

Targeting lung macrophages for fungal and parasitic pulmonary infections with innovative amphotericin B dry powder inhalers

The incidence of fungal pulmonary infections is known to be on the increase, and yet there is an alarming gap in terms of marketed antifungal therapies that are available for pulmonary administration. Amphotericin B (AmB) is a highly efficient broad-spectrum antifungal only marketed as an intravenous formulation. Based on the lack of effective antifungal and antiparasitic pulmonary treatments, the aim of this study was to develop a carbohydrate-based AmB dry powder inhaler (DPI) formulation, prepared by spray drying. Amorphous AmB microparticles were developed by combining 39.7 % AmB with 39.7 % γ-cyclodextrin, 8.1 % mannose and 12.5 % leucine. An increase in the mannose concentration from 8.1 to 29.8 %, led to partial drug crystallisation. Both formulations showed good in vitro lung deposition characteristics (80 % FPF < 5 µm and MMAD < 3 µm) at different air flow rates (60 and 30 L/min) when used with a DPI, but also during nebulisation upon reconstitution in water.

Population pharmacokinetic/pharmacodynamic study suggests continuous infusion of ceftaroline daily dose in ventilated critical care patients with early-onset pneumonia and augmented renal clearance

OBJECTIVES

Ceftaroline could be suitable to treat early-onset ventilator-associated pneumonia (VAP) because of its antibacterial spectrum. However, augmented renal clearance (ARC) is frequent in ICU patients and may affect ceftaroline pharmacokinetics and efficacy. The objective of the study was to explore the impact of ARC on ceftaroline pharmacokinetics and evaluate whether the currently recommended dosing regimen (600 mg every 12 h) is appropriate to treat VAP in ICU patients.

METHODS

A population pharmacokinetic model was developed using pharmacokinetic data from 18 patients with measured creatinine clearance (CLCR) ranging between 83 and 309 mL/min. Monte Carlo simulations were conducted to determine the PTA and the cumulative fraction of response (CFR) against Streptococcus pneumoniae and MRSA for five dosing regimens. Study registered at ClinicalTrials.gov (NCT03025841).

RESULTS

Ceftaroline clearance increased non-linearly with CLCR, with lower concentrations and lower probability of reaching pharmacokinetic/pharmacodynamic targets when CLCR increases. For the currently recommended dosing regimen, the probability of having unbound ceftaroline concentrations above the MIC over the entire dose range is greater than 90% for MICs below 0.125 mg/L. Considering the distribution of MICs, this regimen would not be effective against MRSA infections (CFR between 21% and 67% depending on CLCR), but would be effective against S. pneumoniae infections (CFR >86%).

CONCLUSIONS

The recommended dosing regimen of ceftaroline seems sufficient for covering S. pneumoniae in ICU patients with ARC, but not for MRSA. Among the dosing regimens tested it appears that a constant infusion (50 mg/h) after a loading dose of 600 mg could be more appropriate for MRSA infections.

PKPD Modeling of the Inoculum Effect of Acinetobacter baumannii on Polymyxin B in vivo

The reduction in antimicrobial activity at high bacterial counts is a microbiological phenomenon known as the inoculum effect (IE). In a previous in vitro study, a significant IE was observed for polymyxin B (PMB) against a clinical isolate of Acinetobacter baumannii, and well described by a new pharmacokinetic-pharmacodynamic model. Few in vivo studies have investigated the impact of inoculum size on survival or antibiotic efficacy. Therefore, our objective was to confirm the influence of inoculum size of this A. baumannii clinical isolate on PMB in vivo effect over time. Pharmacokinetics and pharmacodynamics of PMB after a single subcutaneous administration (1, 15 and 40 mg/kg) were studied in a neutropenic murine thigh infection model. The impact of A. baumannii inoculum size (10⁵, 10⁶ and 10⁷ CFU/thigh) on PMB efficacy was also evaluated. In vivo PMB PK was well described by a two-compartment model including saturable absorption from the subcutaneous injection site and linear elimination. The previous in vitro PD model was modified to adequately describe the decrease of PMB efficacy with increased inoculum size in infected mice. The IE was modeled as a decrease of 32% in the in vivo PMB bactericidal effect when the starting inoculum increases from 10⁵ to 10⁷ CFU/thigh. Although not as important as previously characterized in vitro an IE was confirmed in vivo.

Clinical Pharmacokinetics of Daptomycin

Due to the low level of resistance observed with daptomycin, this antibiotic has an important place in the treatment of severe Gram-positive infections. It is the first-in-class of the group of calcium-dependent, membrane-binding lipopeptides, and is a cyclic peptide constituted of 13 amino acids and an n-decanoyl fatty acid chain. The antibacterial action of daptomycin requires its complexation with calcium. Daptomycin is not absorbed from the gastrointestinal tract and needs to be administered parenterally. The distribution of daptomycin is limited (volume of distribution of 0.1 L/kg in healthy volunteers) due to its negative charge at physiological pH and its high binding to plasma proteins (about 90%). Its elimination is mainly renal, with about 50% of the dose excreted unchanged in the urine, justifying dosage adjustment for patients with renal insufficiency. The pharmacokinetics of daptomycin are altered under certain pathophysiological conditions, resulting in high interindividual variability. As a result, therapeutic drug monitoring of daptomycin may be of interest for certain patients, such as intensive care unit patients, patients with renal or hepatic insufficiency, dialysis patients, obese patients, or children. A target for the ratio of the area under the curve to the minimum inhibitory concentration > 666 is usually recommended for clinical efficacy, whereas in order to limit the risk of undesirable muscular effects the residual concentration should not exceed 24.3 mg/L.

Semimechanistic Pharmacodynamic Modeling of Aztreonam-Avibactam Combination to Understand Its Antimicrobial Activity Against Multidrug-Resistant Gram-Negative Bacteria

Aztreonam‐avibactam (ATM‐AVI) is a promising combination to treat serious infections caused by multidrug‐resistant (MDR) pathogens. Three distinct mechanisms of action have been previously characterized for AVI: inhibition of ATM degradation by β‐lactamases, proper bactericidal effect, and enhancement of ATM bactericidal activity. The aim of this study was to quantify the individual contribution of each of the three AVI effects. In vitro static time‐kill studies were performed on four MDREnterobacteriaceae with different β‐lactamase profiles. β‐Lactamase activity was characterized by measuring ATM concentrations over 27 hours. Data were analyzed by a semimechanistic pharmacodynamics modeling approach. Surprisingly, even though AVI prevented ATM degradation, the combined bactericidal activity was mostly explained by the enhancement of ATM effect within clinical range of ATM (5–125 mg/L) and AVI concentrations (0.9–22.5 mg/L). Therefore, when selecting a β‐lactamase inhibitor for combination with a β‐lactam, its capability to enhance the β‐lactam activity should be considered in addition to the spectrum of β‐lactamases inhibited.

Cerebrospinal fluid pharmacokinetics of ceftaroline in neurosurgical patients with an external ventricular drain

BACKGROUND

Owing to its antibacterial properties, ceftaroline could be attractive for prevention or treatment of bacterial post-neurosurgical meningitis/ventriculitis. However, few data are available concerning its meningeal concentrations.

OBJECTIVES

To investigate ceftaroline CSF pharmacokinetics in ICU patients with an external ventricular drain (EVD).

METHODS

Patients received a single 600 mg dose of ceftaroline as a 1 h intravenous infusion. Blood and CSF samples were collected before and 0.5, 1, 3, 6, 12 and 24 h after the end of the infusion. Concentrations were assayed in plasma and CSF by LC-MS/MS. A two-step compartmental pharmacokinetic analysis was conducted. Ceftaroline plasma data were first analysed, and thereafter plasma parameters estimated and corrected for protein binding of 20% were fixed to fit unbound CSF concentrations. In the final model, parameters for both plasma and CSF data were simultaneously estimated.

RESULTS

Nine patients with an EVD were included. The Cmax was 18.29 ± 3.33 mg/L in plasma (total concentrations) and at 0.22 ± 0.17 mg/L in CSF (unbound concentration). The model-estimated CSF input/CSF output clearance ratio was 9.4%, attesting to extensive efflux transport at the blood-CSF barrier.

CONCLUSIONS

Ceftaroline CSF concentrations are too low to ensure prophylactic protection against most pathogens with MICs between 1 and 2 mg/L, owing to its limited central distribution.