Metabolomics unveil key pathways underlying the synergistic activities of aztreonam and avibactam against multidrug-resistant Escherichia coli.

PURPOSE: Aztreonam/avibactam is effective against serious infections caused by Gram-negative bacteria including Enterobacterales harboring metallo-ß-lactamases. While the utility of this combination has been established in vitro and in clinical trials, the purpose of this study is to enhance our understanding of the underlying mechanism responsible for their activities through metabolomic profiling of a multidrug-resistant Escherichia coli clinical isolate. METHODS: Metabolomic analyses of time-dependent changes in endogenous bacterial metabolites in a clinical isolate of a multidrug-resistant E. coli treated with aztreonam and avibactam were performed. E. coli metabolomes were compared at 15 min, 1 h and 24 h following treatments with either avibactam (4 mg/L), aztreonam (4 mg/L), or aztreonam (4 mg/L) + avibactam (4 mg/L). RESULTS: Drug treatment affected 326 metabolites with magnitude changes of at least 2-fold, most of which are involved primarily in peptidoglycan biosynthesis, nucleotide metabolism, and lipid metabolism. The feedstocks for peptidoglycan synthesis were depleted by aztreonam/avibactam combination; a significant downstream increase in nucleotide metabolites and a release of lipids were observed at the three timepoints. CONCLUSION: The findings indicate that the aztreonam/avibactam combination accelerates structural damage to the bacterial membrane structure and their actions were immediate and sustained compared to aztreonam or avibactam alone. By inhibiting the production of crucial cell wall precursors, the combination may have inflicted damages on bacterial DNA.

Physiologically based pharmacokinetic modelling to inform combination dosing regimens of ceftaroline and daptomycin in special populations.

AIMS: The combination of daptomycin and ceftaroline used as salvage therapy is associated with higher survival and decreased clinical failure in complicated methicillin-resistant Staphylococcus aureus (MRSA) infections that are resistant to standard MRSA treatment. This study aimed to evaluate dosing regimens for coadministration of daptomycin and ceftaroline in special populations including paediatrics, renally impaired (RI), obese and geriatrics that generate sufficient coverage against daptomycin-resistant MRSA. METHODS: Physiologically based pharmacokinetic models were developed from pharmacokinetic studies of healthy adults, geriatric, paediatric, obese and RI patients. The predicted profiles were used to evaluate joint probability of target attainment (PTA), as well as tissue-to-plasma ratios. RESULTS: The adult dosing regimens of 6 mg/kg every (q)24h or q48h daptomycin and 300-600 mg q12h ceftaroline fosamil by RI categories achieved ≥90% joint PTA when the minimum inhibitory concentrations in the combination are at or below 1 and 4 µg/mL against MRSA. In paediatrics, wherein there is no recommended daptomycin dosing regimen for S. aureus bacteraemia, ≥90% joint PTA is achieved when the minimum inhibitory concentrations in the combination are up to 0.5 and 2 µg/mL for standard paediatric dosing regimens of 7 mg/kg q24h daptomycin and 12 mg/kg q8h ceftaroline fosamil. Model predicted tissue-to-plasma ratios of 0.3 and 0.7 in the skin and lung, respectively, for ceftaroline and 0.8 in the skin for daptomycin. CONCLUSION: Our work illustrates how physiologically based pharmacokinetic modelling can inform appropriate dosing of adult and paediatric patients and thereby enable prediction of target attainment in the patients during multitherapies.

Aztreonam/avibactam effect on pharmacodynamic indices for mutant selection of Escherichia coli and Klebsiella pneumoniae harbouring serine- and New Delhi metallo-ß-lactamases.

OBJECTIVES: Ceftazidime/avibactam is not active against MBL-producing bacteria. Combining ceftazidime/avibactam or avibactam with aztreonam can counter the resistance of MBL-producing Enterobacterales. The aim of this study was to evaluate whether the addition of avibactam could reduce or close the mutant selection window (MSW) of aztreonam in Escherichia coli and Klebsiella pneumoniae harbouring MBLs; MSW is a pharmacodynamic (PD) parameter for the selection of emergent resistant mutants. METHODS: In vitro susceptibility of 19 clinical isolates to ceftazidime/avibactam, aztreonam alone, and in co-administration (aztreonam/ceftazidime/avibactam and aztreonam/avibactam) was determined, as well as the mutant prevention concentration (MPC). The fraction of time within 24 h that the free drug concentration was within the MSW (fTMSW) and the fraction of time that the free drug concentration was above the MPC (fT>MPC) in both plasma and epithelial lining fluid (ELF) were determined from simulations of 10 000 profiles. The joint PTA was used to derive a joint cumulative fraction of response (CFR). RESULTS: All isolates were resistant to ceftazidime/avibactam or aztreonam. Combining aztreonam and avibactam or ceftazidime/avibactam resulted in synergistic bactericidal activities against all isolates. Synergism was primarily due to the aztreonam/avibactam combination. For aztreonam/avibactam dosing regimens evaluated in clinical trials, fT>MPC values were >90% and >80%, whereas fTMSW measures were <10% and <20% in plasma and ELF, respectively. The CFR was 100% for aztreonam/avibactam against the collection of clinical isolates. CONCLUSIONS: Effective antimicrobial combination optimized the PD parameters measuring selection for emergent mutants by increasing fT>MPC and reducing fTMSW.

Physiologically based pharmacokinetic-pharmacodynamic evaluation of meropenem plus fosfomycin in paediatrics.

AIMS: The objective of the current study was to evaluate paediatric dosing regimens for meropenem plus fosfomycin that generate sufficient coverage against multidrug-resistant bacteria. METHODS: The physiologically based pharmacokinetic (PBPK) models of meropenem and fosfomycin were developed from previously published pharmacokinetic studies in five populations: healthy subjects of Japanese origin, and healthy adults, geriatric, paediatric and renally impaired of primarily Caucasian origins. Pharmacodynamic (PD) analyses were carried out by evaluating dosing regimens that achieved a ≥90% joint probability of target attainment (PTA), which was defined as the minimum of the marginal probabilities to achieve the target PD index of each antibiotic. For meropenem, the percentage of time over a 24-hour period wherein the free drug concentration was above the minimum inhibitory concentration (fT > MIC) of at least 40% was its PD target. The fosfomycin PD index was described by fAUC/MIC of at least 40.8. RESULTS: For coadministration consisting of 20 mg/kg meropenem q8h as a 3-hour infusion and 35 mg/kg fosfomycin q8h also as a 3-hour infusion in a virtual paediatric population between 1 month and 12 years of age with normal renal function and a corresponding body weight between 3 and 50 kg, a joint PTA ≥ 90% is achieved at MICs of 16 and 64 mg/L for meropenem and fosfomycin coadministration, respectively, against Klebsiella pneumoniae and Pseudomonas aeruginosa. CONCLUSION: The current study identified potentially effective paediatric dosing regimens for meropenem plus fosfomycin coadministration against multidrug-resistant bacteria.

Pharmacokinetics, Pharmacodynamics and Dermal Distribution of 5-Methoxypsoralen Based on a Physiologically Based Pharmacokinetic Model to Support Phytotherapy Using Brosimum gaudichaudii.

The treatment of vitiligo includes the combination of psoralens and ultraviolet type A exposure. Psoralens belong to a group of natural furanocoumarins that cause the skin to become sensitive temporarily to ultraviolet type A. The aim of this study was to develop a physiologically based pharmacokinetic model of 5-MOP from Brosimum gaudichaudii to support psoralen and ultraviolet type A therapy. A study of rats was used to establish and validate rat tissue distribution. The same chemical-specific parameters used in the rat model were also employed in the human model to project human pharmacokinetics. The highest exposures in the rats were in the brain and skin. Following a single dose of 1.2 mg/kg 5-MOP in humans, the model predicted a maximum concentration of 20 ng/mL and an area under the curve of 125 ng.h/mL, matching clinical results. The half-maximum melanogenesis concentrations in B16F10 cells were 29.5, 18.5, 11.5, and 6.5 ng/mL for synthetic 5-MOP, synthetic 5-MOP with ultraviolet type A, B. gaudichaudii alone, and B. gaudichaudii plus ultraviolet type A, respectively. Physiologically based pharmacokinetic model prediction in humans supported a once-every-two-day regimen for optimal melanin production. This type of framework can be applied to support strategies for dose selection and to investigate the impact of drugs on melanocyte recovery.

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.

Physiologically-based pharmacokinetics of ziprasidone in pregnant women.

AIMS: Pregnancy is associated with physiological changes that alter the pharmacokinetics (PK) of drugs. The aim of this study was to predict the PK of ziprasidone in pregnant women. METHODS: A full physiologically-based pharmacokinetic (PBPK) model of ziprasidone was developed and validated for the non-pregnant population (healthy adults, paediatrics, geriatrics), and this was extended to the pregnant state to assess the change in PK profile of ziprasidone throughout pregnancy. RESULTS: The PBPK model successfully predicted the ziprasidone disposition in healthy adult volunteers, wherein the predicted and observed AUC, Cmax and tmax were within the fold-difference of 0.94-1.09, 0.89-1.40 and 0.80-1.08, respectively. The paediatric and geriatric population, also showed predicted AUC, Cmax and tmax within a two-fold range of the observed values. The simulated exposure in pregnant women using a p-PBPK model showed no significant difference when compared to non-pregnant women. CONCLUSIONS: The PBPK model predicted the impact of physiological changes during pregnancy on PK and exposure of ziprasidone, suggesting that dose adjustment is not necessary in this special population.

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.

Pharmacodynamic Evaluation of Fosfomycin against Escherichia coli and Klebsiella spp. from Urinary Tract Infections and the Influence of pH on Fosfomycin Activities.

Fosfomycin is widely used for the treatment of uncomplicated urinary tract infection (UTI), and it has recently been recommended that fosfomycin be used to treat infections caused by multidrug-resistant (MDR) Gram-negative bacilli. Whether urine acidification can improve bacterial susceptibility to fosfomycin oral dosing regimens has not been analyzed. The MIC of fosfomycin for 245 Gram-negative bacterial isolates, consisting of 158 Escherichia coli isolates and 87 Klebsiella isolates which were collected from patients with urinary tract infections, were determined at pH 6.0 and 7.0 using the agar dilution method. Monte Carlo simulation of the urinary fosfomycin area under the concentration-time curve (AUC) after a single oral dose of 3,000 mg fosfomycin and the MIC distribution were used to determine the probability of target attainment (PTA). Fosfomycin was effective against E. coli (MIC90 ≤ 16 µg/ml) but not against Klebsiella spp. (MIC90 > 512 µg/ml). Acidification of the environment increased the susceptibility of 71% of the bacterial isolates and resulted in a statistically significant decrease in bacterial survival. The use of a regimen consisting of a single oral dose of fosfomycin against an E. coli isolate with an MIC of ≤64 mg/liter was able to achieve a PTA of ≥90% for a target pharmacodynamic index (AUC/MIC) of 23 in urine; PTA was not achieved when the MIC was higher than 64 mg/liter. The cumulative fractions of the bacterial responses (CFR) were 99% and 55% against E. coli and Klebsiella spp., respectively, based on simulated drug exposure in urine with an acidic pH of 6.0. A decrease of the pH from 7.0 to 6.0 improved the PTA and CFR of the target pharmacodynamic index in both E. coli and Klebsiella isolates.

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.

Pharmacodynamic Evaluation of the Potential Clinical Utility of Fosfomycin and Meropenem in Combination Therapy against KPC-2-Producing Klebsiella pneumoniae.

KPC-producing Klebsiella pneumoniae causes serious infections associated with high death rates worldwide. Combination therapy consisting of fosfomycin and a carbapenem is better than monotherapy to combat multidrug-resistant microorganisms, but no dosages for the combination have been defined. The MICs of meropenem and fosfomycin were evaluated against 18 clinical isolates of KPC-2-producing K. pneumoniae The activities of combination antimicrobials were also determined by the checkerboard method. The MIC50 and MIC90 of each agent alone and in combination were challenged against short (1.5-h) or prolonged (3-h) infusion regimens of meropenem (1 g every 8 h [q8h], 1.5 g q6h, 2 g q8h) and fosfomycin (4 g q8h, 6 g q6h, 8 g q8h) by Monte Carlo simulation to evaluate the time above the MIC of the free drug concentration as a percentage of the dosing interval (fT>MIC). The monotherapy MIC50s and MIC90s were 32 and 256 mg/liter for meropenem and 64 and 512 mg/liter for fosfomycin, respectively. Antimicrobial combination increased bacterial susceptibility to 1/4 the MIC50s and to 1/8 to 1/16 the MIC90s of monotherapy. The antimicrobial combination demonstrated a synergistic effect for at least two-thirds of the isolates. In combination therapy, fosfomycin regimens of 6 g q6h and 8 g q8h as a 3-h infusion against the MIC50 and MIC90 had better chances of achieving ≥90% probability of target attainment (PTA) of 70% fT>MIC. Meropenem regimens of 1.5 g q6h and 2 g q8h in prolonged infusion can achieve close to 90% PTA of 40% fT>MIC for MIC50 but not MIC90 The significant reduction in the MIC values and the achievement of appropriate PTA demonstrated that regimens containing fosfomycin with meropenem can be effective against KPC-2-producing K. pneumoniae.

Gentamicin dosing strategy in patients with end-stage renal disease receiving haemodialysis: evaluation using a semi-mechanistic pharmacokinetic/pharmacodynamic model.

OBJECTIVES: Gentamicin is widely used in end-stage renal disease (ESRD) patients for the treatment of infections. The goal of this study was to find the most reasonable dosing regimen for gentamicin in ESRD patients receiving haemodialysis. METHODS: The in vitro antimicrobial activity of gentamicin was evaluated by static and dynamic time-kill experiments against three bacterial strains of MSSA, MRSA and Pseudomonas aeruginosa. A semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model was established afterwards, allowing the characterization of the antibacterial effect of gentamicin in the human body. The model was utilized to assess dosing regimens of gentamicin in ESRD patients receiving haemodialysis, taking both efficacy and safety into account. RESULTS: The PK/PD model was capable of describing the bacterial response to gentamicin exposure in all three strains. Simulation based on the PK/PD model showed that pre-dialysis and post-dialysis dosing would bring comparable benefit to the ESRD patient regardless of whether the PK/PD target (fCmax/MIC >8-fold) was achieved, while the post-dialysis dosing resulted in a significantly lower trough concentration. The result of simulated dose fractionation demonstrated that both fCmax/MIC and fAUC(0-24)/MIC are strong predictors of drug effectiveness, but the PK/PD model would provide a more precise prediction of antibacterial activity as well as valuable information on dose selection in ESRD patients receiving haemodialysis. CONCLUSIONS: Our study supports the original FDA label with regard to the dosing regimen of gentamicin in ESRD patients, which offers adequate clinical benefit as well as an acceptable safety profile.

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.

Rapid and efficient method for the quantification of lychnopholide in rat plasma by liquid chromatography-tandem mass spectrometry for pharmacokinetic application.

Lychnopholide is a sesquiterpene lactone usually obtained from Lychnophora and Eremanthus species and has pharmacological activities that include anti-inflammatory and anti-tumor. Lychnopholide isolated from Eremanthus matogrossenssis was analyzed in this study. The aims of this study were to develop and validate an analytical methodology by LC-MS/MS and to quantify lychnopholide in rat plasma. Chromatographic separation was achieved on a C18 column using isocratic elution with the mobile phase consisting of methanol and water (containing 0.1% formic acid) at a flow rate of 0.4 mL/min. The detection was performed in multiple-reaction monitoring mode using electrospray ionization in positive mode. The method validation was performed in accordance with regulatory guidelines and the results met the acceptance criteria. The linear range of detection was 10-200 ng/mL (r > 0.9961). The intra- and inter-day assay variability were <6.2 and <11.7%, respectively. The extraction recovery was approximately 63% using liquid-liquid extraction with chloroform. Lychnopholide was detected in plasma up to 60 min after intravenous administration in rats. This rapid and sensitive method for the analysis of the sesquiterpene lactone lychnopholide in rat plasma can be applied to pharmacokinetic studies of this compound. Copyright © 2016 John Wiley & Sons, Ltd.

N-acetyltransferase genotypes and the pharmacokinetics and tolerability of para-aminosalicylic acid in patients with drug-resistant pulmonary tuberculosis.

The aim of this study was to examine the relationships between N-acetyltransferase genotypes, pharmacokinetics, and tolerability of granular slow-release para-aminosalicylic acid (GSR-PAS) in tuberculosis patients. The study was a randomized, two-period, open-label, crossover design wherein each patient received 4 g GSR-PAS twice daily or 8 g once daily alternately. The PAS concentration-time profiles were modeled by a one-compartment disposition model with three transit compartments in series to describe its absorption. Patients' NAT1 and NAT2 genotypes were determined by sequencing and restriction enzyme analysis, respectively. The number of daily vomits was modeled by a Poisson probability mass function. Comparisons of other tolerability measures by regimens, gender, and genotypes were evaluated by a linear mixed-effects model. The covariate effects associated with efavirenz, gender, and NAT1*3, NAT1*14, and NAT2*5 alleles corresponded to 25, 37, -17, -48, and -27% changes, respectively, in oral clearance of PAS. The NAT1*10 allele did not influence drug clearance. The time above the MIC of 1 mg/liter was significantly different between the two regimens but not influenced by the NAT1 or NAT2 genotypes. The occurrence and intensity of intolerance differed little between regimens. Four grams of GSR-PAS twice daily but not 8 g once daily ensured concentrations exceeding the MIC (1 mg/liter) throughout the dosing interval; PAS intolerance was not related to maximum PAS concentrations over the doses studied and was not more frequent after once-daily dosing. We confirm that the slow phenotype conferred by the NAT1*14 and NAT1*3 alleles resulted in higher PAS exposure but found no evidence of increased activity of the NAT1*10 allele.

Simultaneous Characterization of Intravenous and Oral Pharmacokinetics of Lychnopholide in Rats by Transit Compartment Model.

The pharmacokinetic properties of a new molecular entity are important aspects in evaluating the viability of the compound as a pharmacological agent. The sesquiterpene lactone lychnopholide exhibits important biological activities. The objective of this study was to characterize the pharmacokinetics of lychnopholide after intravenous administration of 1.65 mg/kg (n = 5) and oral administration of 3.3 mg/kg (n = 3) lychnopholide in rats (0.2 ± 0.02 kg in weight) through nonlinear mixed effects modeling and non-compartmental pharmacokinetic analysis. A highly sensitive analytical method was used to quantify the plasma lychnopholide concentrations in rats. Plasma protein binding of this compound was over 99 % as determined by a filtration method. A two-compartment body model plus three transit compartments to characterize the absorption process best described the disposition of lychnopholide after both routes of administration. The oral bioavailability was approximately 68 %. The clearance was 0.131 l/min and intercompartmental clearance was 0.171 l/min; steady-state volume of distribution was 4.83 l. The mean transit time for the absorption process was 9.15 minutes. No flip-flop phenomenon was observed after oral administration. The pharmacokinetic properties are favorable for further development of lychnopholide as a potential oral pharmacological agent.

Pharmacokinetic evaluation of avicularin using a model-based development approach.

The aim of this study was to use the pharmacokinetic information of avicularin in rats to project a dose for humans using allometric scaling. A highly sensitive and specific bioanalytical assay to determine avicularin concentrations in the plasma was developed and validated for UPLC-MS/MS. The plasma protein binding of avicularin in rat plasma determined by the ultrafiltration method was 64%. The pharmacokinetics of avicularin in nine rats was studied following an intravenous bolus administration of 1 mg/kg and was found to be best described by a two-compartment model using a nonlinear mixed effects modeling approach. The pharmacokinetic parameters were allometrically scaled by body weight and centered to the median rat weight of 0.23 kg, with the power coefficient fixed at 0.75 for clearance and 1 for volume parameters. Avicularin was rapidly eliminated from the systemic circulation within 1 h post-dose, and the avicularin pharmacokinetic was linear up to 5 mg/kg based on exposure comparison to literature data for a 5-mg/kg single dose in rats. Using allometric scaling and Monte Carlo simulation approaches, the rat doses of 1 and 5 mg/kg correspond to the human equivalent doses of 30 and 150 mg, respectively, to achieve comparable plasma avicularin concentrations in humans.

Estimation of intracellular concentration of stavudine triphosphate in HIV-infected children given a reduced dose of 0.5 milligrams per kilogram twice daily.

The antiviral efficacy of stavudine depends on the trough concentration of its intracellular metabolite, stavudine-triphosphate (d4T-TP), while the degree of stavudine's mitochondrial toxicity depends on its peak concentration. Rates of mitochondrial toxicity are high when stavudine is used at the current standard pediatric dose (1 mg/kg twice daily [BID]). Evidence from adult work suggests that half of the original standard adult dose (i.e., 20 mg BID) may be equally effective, with markedly less mitochondrial toxicity. We present a population pharmacokinetic model to predict intracellular d4T-TP concentrations in pediatric HIV-infected patients administered a dose of 0.5 mg/kg BID. Our model predicted that the reduced pediatric dose would result in a trough intracellular d4T-TP concentration above that of the reduced 20-mg adult dose and a peak concentration below that of the 20-mg adult dose. The simulated pediatric intracellular d4T-TP at 0.5 mg/kg BID resulted in median peak and trough values of approximately 23.9 fmol/10(6) cells (95% prediction interval [PI], 14.2 to 41 fmol/10(6) cells) and 14.8 fmol/10(6) cells (95% PI, 7.2 to 31 fmol/10(6) cells), respectively. The peak and trough concentrations resulting from a 20-mg BID adult dose were 28.4 fmol/10(6) cells (95% PI, 17.3 to 45.5 fmol/10(6) cells) and 13 fmol/10(6) cells (95% PI, 6.8 to 28.6 fmol/10(6) cells), respectively. Halving the current standard pediatric dose should therefore not compromise antiviral efficacy, while markedly reducing mitochondrial toxicity.

Pharmacokinetics of para-aminosalicylic acid in HIV-uninfected and HIV-coinfected tuberculosis patients receiving antiretroviral therapy, managed for multidrug-resistant and extensively drug-resistant tuberculosis.

The emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis prompted the reintroduction of para-aminosalicylic acid (PAS) to protect companion anti-tuberculosis drugs from additional acquired resistance. In sub-Saharan Africa, MDR/XDR tuberculosis with HIV coinfection is common, and concurrent treatment of HIV infection and MDR/XDR tuberculosis is required. Out of necessity, patients receive multiple drugs, and PAS therapy is frequent; however, neither potential drug interactions nor the effects of HIV infection are known. Potential drug-drug interaction with PAS and the effect of HIV infection was examined in 73 pulmonary tuberculosis patients; 22 (30.1%) were HIV coinfected. Forty-one pulmonary MDR or XDR tuberculosis patients received 4 g PAS twice daily, and in a second crossover study, another 32 patients were randomized, receiving 4 g PAS twice daily or 8 g PAS once daily. A PAS population pharmacokinetic model in two dosing regimens was developed; potential covariates affecting its pharmacokinetics were examined, and Monte Carlo simulations were conducted evaluating the pharmacokinetic-pharmacodynamic index. The probability of target attainment (PTA) to maintain PAS levels above MIC during the dosing interval was estimated by simulation of once-, twice-, and thrice-daily dosing regimens not exceeding 12 g daily. Concurrent efavirenz (EFV) medication resulted in a 52% increase in PAS clearance and a corresponding >30% reduction in mean PAS area under the concentration curve in 19 of 22 HIV-M. tuberculosis-coinfected patients. Current practice recommends maintenance of PAS concentrations at ≥1 µg/ml (the MIC of M. tuberculosis), but the model predicts that at only a minimum dose of 4 g twice daily can this PTA be achieved in at least 90% of the population, whether or not EFV is concomitantly administered. Once-daily dosing of 12 g PAS will not provide PAS concentrations exceeding the MIC over the entire dosing interval if coadministered with EFV, while 4 g twice daily ensures concentrations exceeding MIC over the entire dosing interval, even in HIV-infected patients who received EFV.

Largazole pharmacokinetics in rats by LC-MS/MS.

A highly sensitive and specific LC-MS/MS method for the quantitation of largazole thiol, the active species of the marine-derived preclinical histone deacetylase inhibitor, largazole (prodrug), was developed and validated. Largazole thiol was extracted with ethyl acetate from human or rat plasma along with the internal standard, harmine. Samples were separated on an Onyx Monolithic C18 column by a stepwise gradient elution with 0.1% formic acid in methanol and 0.1% aqueous formic acid employing multiple reaction monitoring (MRM) detection. Linear calibration curves were obtained in the range of 12.5-400 ng/mL with 200 µL of human plasma. The overall intra-day precision was from 3.87% to 12.6%, and the inter-day precision was from 7.12% to 9.8%. The accuracy at low, medium and high concentrations ranged from 101.55% to 105.84%. Plasma protein bindings of largazole thiol in human and rat plasma as determined by an ultrafiltration method were 90.13% and 77.14%, respectively. Plasma drug concentrations were measured by this LC-MS/MS method. The pharmacokinetics of largazole thiol in rats was studied following i.v. administration at 10 mg/kg and found to follow a two-compartment model. Largazole thiol was rapidly eliminated from systemic circulation within 2 h. The established LC-MS/MS method is suitable for the analysis of largazole thiol in human plasma, as well.