Physiologically-based pharmacokinetic modeling to inform dosing regimens and routes of administration of rifampicin and colistin combination against Acinetobacter baumannii.

BACKGROUND: Carbapenem-resistant Acinetobacter baumannii (CRAB) is resistant to major antibiotics such as penicillin, cephalosporin, fluoroquinolone and aminoglycoside, and has become a significant nosocomial pathogen. The efficacy of rifampicin and colistin combination against CRAB could be dependent on the administration routes and drug concentrations at the site of infection. OBJECTIVE: The objective is to predict drug disposition in biological tissues. Treatment efficacy is extrapolated by assessing respective pharmacodynamic (PD) indices, as well as parameters associated with the emergence of resistance. METHODS: Physiologically-based pharmacokinetic models of rifampicin and colistin were utilized to predict tissue exposures. Dosing regimens and administration routes for combination therapy were evaluated in terms of in vitro antimicrobial susceptibility of A. baumannii associated with targeted PD indices and resistance parameters. RESULTS: Simulated exposures in blood, heart, lung, skin and brain were consistent with reported penetration rates. The results demonstrated that a combination of colistin and rifampicin using conventional intravenous (i.v.) doses could achieve effective exposures in the blood and skin. However, for lung infections, colistin by inhalation would be required due to low lung penetration from intravenous route. Inhaled colistin alone provided good PD coverage but this practice could encourage the emergence of additional resistance which may be overcome by a combination regimen that includes inhaled rifampicin. CONCLUSION: This in silico extrapolation provides valuable information on dosing regimens and routes of administration against CRAB infections in specific tissues. The PBPK modeling approach could be a non-invasive way to inform therapeutic benefits of combination antimicrobial therapy.

The combination effect of meropenem/sulbactam/polymyxin-B on the pharmacodynamic parameters for mutant selection windows against carbapenem-resistant Acinetobacter baumannii.

The objective of this study was to evaluate whether combinations of sulbactam, meropenem, and polymyxin-B could reduce or close the gap of mutant selection window (MSW) of individual antibiotics against Acinetobacter baumannii harboring OXA-23. MICs of three antimicrobials used alone and in combination (meropenem/polymyxin-B or meropenem/polymyxin-B/sulbactam) were obtained in 11 clinical isolates and mutant prevention concentrations were determined in 4 of the 11 isolates. All isolates were resistant to meropenem or polymyxin-B. Combining meropenem and polymyxin-B with or without sulbactam resulted in synergistic bactericidal activities. Pharmacokinetic (PK) simulations of drug concentrations in the blood and epithelial lining fluid coupled with pharmacodynamic (PD) evaluations revealed that the fractions of time over the 24-h in terms of free drug concentration within the MSW (fTMSW) and above the MPC (fT>MPC) were optimized by combination therapy. The resultant clinical regimens of meropenem, polymyxin-B, and sulbactam evaluated in the PK-PD analysis were 2 g q8h, 2.5 mg/kg loading dose followed by 1.5 mg/kg q12h, and 3 g q8h, respectively, in patients with normal renal function. Subsequent corresponding equivalent exposure regimens would depend on the extent of renal failure. The overall results indicate that combination antibiotics consisting of sulbactam/meropenem/polymyxin-B can confer potential efficacy against A. baumannii harboring OXA-23, and reduce the opportunity for bacteria to develop further resistance. This study provides a framework for pharmacodynamic evaluation of drug-resistant mutant suppression in an antimicrobial co-administration setting. The results thereby lay the groundwork for additional studies and future clinical confirmation is warranted.

Metabolomic profiling of polymyxin-B in combination with meropenem and sulbactam against multi-drug resistant Acinetobacter baumannii.

Empirical therapies using polymyxins combined with other antibiotics are recommended in the treatment of Acinetobacter baumannii infections. In the present study, the synergistic activities of polymyxin-B, meropenem, and sulbactam as combination therapy were investigated using metabolomic analysis. The metabolome of A. baumannii was investigated after treatment with polymyxin-B alone (2 mg/l), meropenem (2 mg/l) alone, combination of polymyxin-B/meropenem at their clinical breakpoints, and triple-antibiotic combination of polymyxin-B/meropenem and 4 mg/l sulbactam. The triple-antibiotic combination significantly changed the metabolite levels involved in cell outer membrane and cell wall biosynthesis, including fatty acid, glycerophospholipid, lipopolysaccharide, peptidoglycan, and nucleotide within 15 min of administration. In contrast, significant changes in metabolome were observed after 1 h in sample treated with either meropenem or polymyxin-B alone. After 1 h of administration, the double and triple combination therapies significantly disrupted nucleotide and amino acid biosynthesis pathways as well as the central carbon metabolism, including pentose phosphate and glycolysis/gluconeogenesis pathways, and tricarboxylic acid cycle. The addition of sulbactam to polymyxin-B and meropenem combination appeared to be an early disruptor of A. baumannii metabolome, which paves the way for further antibiotic penetration into bacteria cells. Combination antibiotics consisting of sulbactam/meropenem/polymyxin-B can effectively confer susceptibility to A. baumannii harboring OXA-23 and other drug resistant genes. Metabolomic profiling reveals underlying mechanisms of synergistic effects of polymyxin-B combined with meropenem and sulbactam against multi-drug resistant A. baumannii.

Prediction of Tissue Exposures of Meropenem, Colistin, and Sulbactam in Pediatrics Using Physiologically Based Pharmacokinetic Modeling.

BACKGROUND: The combination of polymyxins, meropenem, and sulbactam demonstrated efficacy against multi-drug-resistant bacillus Acinetobacter baumannii. These three antibiotics are commonly used against major blood, skin, lung, and heart muscle infections. OBJECTIVE: The objective of this study was to predict drug disposition and extrapolate the efficacy in these tissues using a physiologically based pharmacokinetic modeling approach that linked drug exposures to their target pharmacodynamic indices associated with antimicrobial activities against A. baumannii. METHODS: An adult physiologically based pharmacokinetic model was developed for meropenem, colistin, and sulbactam and scaled to pediatrics accounting for both renal and non-renal clearances. The model reliability was evaluated by comparing simulated plasma and tissue drug exposures to observed data. Target pharmacodynamic indices were used to evaluate whether pediatric and adult dosing regimens provided sufficient coverage. RESULTS: The modeled plasma drug exposures in adults and pediatric patients were consistent with reported literature data. The mean fold errors for meropenem, colistin, and sulbactam were in the range of 0.710-1.37, 0.981-1.47, and 0.647-1.39, respectively. Simulated exposures in the blood, skin, lung, and heart were consistent with reported penetration rates. In a virtual pediatric population aged from 2 to < 18 years, the interpretive breakpoints were achieved in 85-90% of subjects for their targeted pharmacodynamic indices after administration of pediatric dosing regimens consisting of 30 mg/kg of meropenem, and 40 mg/kg of sulbactam three times daily as a 3-h or continuous infusion and 5 mg/kg/day of colistin base activity. CONCLUSIONS: The physiologically based pharmacokinetic modeling supports pediatric dosing regimens of meropenem/colistin/sulbactam in a co-administration setting against infections in the blood, lung, skin, and heart tissues due to A. baumannii.

Revamping the ever-changing landscape of drug development processes in the midst of COVID-19 pandemic.

Oncology is the frontline of drug development. The current pharmaceutical pipeline is disproportional focused on oncology, where about 1/3 of all phases of development is in this therapeutic area. The emphasis brings about substantial breakthroughs and has made positive impact on the quality of life. However, oncology remains a threat to human existence. To facilitate this process, a comprehensive list of novel/first molecularly targeted oncology drug approvals by the FDA from 2017 to 2020 is assessed. Here, we focus on molecularly targeted oncology drugs and not cytotoxic ones, although the latter remain important. To achieve this purpose, besides their sponsors, years of approval, drug classes, and cancer indications, clinical significance is included. The results show that approved molecularly targeted drugs span across diverse classes, including small molecule receptor inhibitors, and biologics such as monoclonal antibodies, antibody-drug conjugates, check-point inhibitors (i.e., PD1, PDL1, CTLA4) and CAR-T cell therapies. Although complete cure of cancer remains limited, we have made substantial inroads and more is yet to come. Moreover, many of these new knowledge can be extrapolated to other therapeutic areas, especially to those of currently unmet medical needs such as in neurology and other chronic diseases.

QT Correction: Using an Observed Regression Factor Applicable to a Population Subset.

PURPOSE: A QT interval correction to standardized heart rate (QTc) is essential to compare drug effect or to mitigate cardiac risk in clinical practice. Numerous empirical formulas for QTc have been proposed. However, an effective and readily comprehensible method has been elusive. As QTc is dependent on demographics, concomitant drugs, health status, autonomic and diurnal variation, the applicability of these methods hinge on the characteristics of a population that is assessed. An individual QTc is ideal, but it requires substantial baseline ECG data and is beyond the scope for initial evaluation. As a compromise, an approach for a 'discontinuous' population subset is suggested. In this article, we outline the challenges of QTc, and select a power function [QTc = QT/{(RR)a}] in which a regression factor a relevant to a particular population subset is used. The formula is similar to the one used in the Bazett's (a=1/2) or Fridericia's (a=1/3) method. The use of this approach is illustrated with two small population subsets separated by age and out- or in-patient status. This QTc approach is relatively simple to implement in drug development or by a busy practitioner within his/her institution. Nevertheless, in view of the limitations of the illustrative sample size and confounding factors of this proposal, additional studies will be necessary for further evaluation of QTc methods.

In vitro and in vivo metabolism of a novel chymase inhibitor, SUN13834, and the predictability of human metabolism using mice with humanized liver.

1. A novel oral chymase inhibitor, SUN13834, is under clinical development for the treatment of atopic dermatitis (AD). In this study, in vitro and in vivo metabolic profiles of SUN13834 were compared between severe combined immunodeficiency (SCID) mice, chimeric mice with humanized liver and humans. 2. In in vitro experiments using liver microsomes, predominant metabolites of SUN13834 were glucuronide (MG-1) in SCID mice and hydroxylated metabolite (M-3) in chimeric mice and humans. 3. After a single oral dose of [(14)C]SUN13834 to SCID and chimeric mice, glucuronidation was the major metabolic pathway in SCID mice, while the parent compound, ring opening form (M-5), O-demethylated form of M-5 (M-6) and glucuronidation of M-6 (M-6G) were detected at higher levels in chimeric mice compared to SCID mice. 4. When AD patients were orally treated using SUN13834 for 28 days, the parent compound had the highest concentration in plasma, and M-6, M-6G, M-5 and MG-1 were identified as major metabolites. 5. This is the first report of SUN13834 metabolic information in human. In addition, based on similarities in metabolic profiles between chimeric mice and humans, it was concluded that chimeric mice are useful for predicting SUN13834 metabolism in humans during early stages of drug development.

A feasibility study of differential delivery of levodopa ester and benserazide using site-specific intestinal loops in rats.

To study the effect of varied intestinal delivery of levodopa ester, levodopa and its butyl ester were administered as bolus or continuous infusions into site-specific, in situ ligated intestinal loops of rats. Benserazide, a carboxylase inhibitor, was not administered, coadministered with ester, or infused into the duodenal loop prior to ester dosing. While the proximal colon minimally absorbed levodopa itself, it substantially absorbed the ester. Coadministration of benserazide and ester at the colon did not increase absorption; however, prior infusion of benserazide into the duodenum enhanced the colonic absorption of ester. Compared to bolus infusion, continuous delivery of the ester resulted in a more sustained levodopa concentration in plasma, and less metabolism into dopamine. The results were repeated for methyl ester, and the relative differences between the results of methyl and butyl esters versus levodopa were similar. The overall results at the duodenum, jejunum, and ileum were also comparable, likewise were those for the proximal, middle, and distal colons. The results of the study are encouraging: a combination of the continuous delivery of levodopa ester with an immediate-release of benserazide optimizes levodopa bioavailability, potentially leading to a much more effective use of levodopa in the treatment of Parkinson's patients.

Population pharmacokinetics of the selective serotonin 5-HT1A receptor partial agonist piclozotan.

BACKGROUND/AIMS: Serotonin (5-HT) and its receptors are known to play important roles in various physiological and pathophysiological processes. The 5-HT1A receptor subtype is thought to be involved in psychiatric disorders, immunomodulation, and in cerebral ischemic conditions. Piclozotan, a selective and potent partial agonist of 5-HT1A, has been shown to be neuroprotective against ischemic neuronal damage in animal models. Its pharmacokinetics (PK), tolerability, and safety have been evaluated in patients with acute ischemic stroke. The aim of the study was to describe piclozotan PK, using population PK modeling. METHODS: A total of 1308 plasma piclozotan concentration measurements from 84 healthy subjects and 412 plasma piclozotan measurements from 74 stroke patients were included in the analysis. Covariates considered during the model building process included disease status, age, weight, sex, smoking status, and alcohol consumption. Data were analyzed using nonlinear mixed-effects modeling with the NONMEM software system. The final model was qualified via predictive check and nonparametric bootstrap procedures. RESULTS: Piclozotan PK was well described using a 3-compartment model with first-order elimination. Parameter estimates (intersubject variability) were V1, central volume: 64.0 L (66.5%) and CL, systemic clearance: 18.0 L/h (31.4%). Peripheral volumes (V2, V3) were related to total body weight, whereas CL was related to ideal body weight. Clearance decreased with advancing age, yielding a decrease of 35%-65% in patients aged 70-90. There was no discernable difference in PK between healthy subjects and stroke patients. CONCLUSIONS: Piclozotan disposition was well described by the population model, and the intersubject variability around the estimated parameters was moderate in magnitude (<60%). The population PK analysis of piclozotan allows for characterization of piclozotan exposure in individual subjects based on their age and body weight. The availability of a population PK model will facilitate dose optimization and further clinical development of piclozotan.

Reciprocating dialysis tube method: periodic tapping improved in vitro release/dissolution testing of suppositories.

The reciprocating dialysis tube (RDT) method can be used for in vitro release/dissolution testing of suppositories and has been reported to show good in vitro and in vivo correlation. However, for suppositories with viscous excipients, the result remains variable and generally under-predicts in vivo absorption. The purpose of this study was to assess whether periodic tapping of the closure of the RDT could improve in vitro release testing of suppositories. Two commercially available acetaminophen suppositories (A and B) that showed characteristic release behavior under normal rectal temperatures (37 and 38 degrees C) were chosen as test suppositories. In the absence of tapping, suppository A showed different release profiles at 37 and 38 degrees C, but the difference disappeared with periodic tapping. This finding was consistent with minimum temperature effect in the rectal absorption of suppository A in rabbits. Suppository B showed distinct release profiles at 37 and 38 degrees C irrespective of tapping, and the rectal absorption of suppository B in rabbits was affected by temperature. The test variability (CV% and ranges of release values) was substantially reduced in the presence of tapping. In conclusion, the addition of periodic tapping to RDT method developed in this study could improve in vitro release testing of suppositories.