Construction of a CYP2J2-Template System and Its Application for Ligand Metabolism Prediction

A Template system for the understanding of human CYP2J2-mediated reactions was constructed from the assembly of the ligands with the introduction of ideas of allowable width, Trigger-residue and the residue-initiated movement of ligands in the active site, which were in common with other Template* systems for human CYP1A1, CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2E1, CYP3A4, CYP3A5, and CYP3A7 (Drug Metab Pharmacokinet 2016, 2017, 2019, 2020, 2021, 2022, 2023, 2024, and in press 2024). CYP2J2 system also includes ideas of bi-molecule binding of ligands on the Template. From their placements on the Template and rules for interaction modes, verifications of good and poor substrates, regio/stereo-selectivity, and inhibitory interaction became available faithfully for these ligands. The refined CYP2J2-Template system will thus offer reliable estimations of this human CYP catalysis toward ligands of diverse structures, together with their deciphering information to lead to judgments.

PharmVar GeneFocus: CYP4F2

The Pharmacogene Variation Consortium (PharmVar) serves as a global repository providing star (*) allele nomenclature for the polymorphic human CYP4F2 gene. CYP4F2 genetic variation impacts the metabolism of vitamin K, which is associated with warfarin dose requirements, and the metabolism of drugs, such as imatinib or fingolimod, and certain endogenous compounds including vitamin E and eicosanoids. This GeneFocus provides a comprehensive overview and summary of CYP4F2 genetic variation including the characterization of 14 novel star alleles, CYP4F2*4 through *17. A description of how haplotype information cataloged by PharmVar is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC) is also provided.

Therapeutic drug monitoring of linezolid and exploring optimal regimens and a toxicity-related nomogram in elderly patients: a multicentre, prospective, non-interventional study

BACKGROUND

The concentrations of linezolid, its optimal regimen and the associated side effects in elderly patients remain unclear.

METHODS

In this multicentre, prospective study, elderly patients receiving linezolid at four tertiary hospitals in Beijing between May 2021 and December 2022 were included. Linezolid concentrations and haematological toxicity were monitored dynamically. Risk factors for linezolid overexposure and moderate-to-severe linezolid-induced thrombocytopenia (M/S LIT) were analysed, and a predictive model of M/S LIT was developed.

RESULTS

A total of 860 linezolid concentrations were measured in 313 patients. The median trough concentrations of linezolid were 24.4 (15.3, 35.8) mg/L at 36-72 h and 26.1 (17.0, 38.1) mg/L at 5-10 days (P = 0.132). Severe linezolid exposure was independently associated with age, estimated glomerular filtration rate (eGFR) and the worst SOFA score (SOFA1), and we further recommended dose regimens for elderly patients based on these findings. The incidences of linezolid-induced thrombocytopenia(LIT) and M/S LIT were 73.5% and 47.6%, respectively. M/S LIT was independently correlated with treatment duration, average trough concentration (TDMa), baseline platelet count, eGFR and baseline SOFA score (SOFA0). The developed nomogram predicted M/S LIT with an area under the curve of 0.767 (95% CI 0.715-0.820), a sensitivity of 71.1% and a specificity of 73.2%.

CONCLUSIONS

Linezolid trough concentrations increased dramatically in the elderly, by about 10 mg/L in patients aged 65-80 years, followed by a further increase of 10 mg/L for every 10 years of age. Therapeutic drug monitoring is recommended in elderly patients receiving linezolid. The developed nomogram may predict M/S LIT and guide dosage adjustments of linezolid. Clinical trial registration number: ChiCTR2100045707.

The effects of drug-drug interaction on linezolid pharmacokinetics: A systematic review

OBJECTIVES

Linezolid is a commonly used antibiotic in the clinical treatment of gram-positive bacterial infections. The impacts of drug interactions on the pharmacokinetics of linezolid are often overlooked. This manuscript aims to review the medications that affect the pharmacokinetics of linezolid.

METHODS

In accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we queried the PubMed, Embase, and Cochrane Library for publications from database establishment to November 3, 2023, using the search terms: "Linezolid" and "interaction," or "interact," or "drug-drug interaction," or "co-treatment," or "cotreatment," or "combined," or "combination."

RESULTS

A total of 24 articles were included. Among the reported medication interactions, rifampicin, levothyroxine, venlafaxine, and phenobarbital could reduce the concentration of linezolid; clarithromycin, digoxin, cyclosporine, proton pump inhibitors, and amiodarone could increase the concentration of linezolid, while aztreonam, phenylpropanolamine, dextromethorphan, antioxidant vitamins, and magnesium-containing antacids had no significant effects on linezolid pharmacokinetics. The ratio of mean (ROM) of linezolid AUC in co-treatment with rifampicin to monotherapy was 0.67 (95%CI 0.58-0.77) and 0.63 (95%CI 0.43-0.91), respectively, in 2 studies, and co-treatment with 500 mg clarithromycin to monotherapy was 1.81 (95%CI 1.49-2.13).

CONCLUSIONS

This systematic review found that numerous drugs have an impact on the pharmacokinetics of linezolid, and the purported main mechanism may be that linezolid is the substrate of P-glycoprotein. In clinical practice, it is prudent to pay attention to the changes in linezolid pharmacokinetics caused by interactions. Conducting therapeutic drug monitoring (TDM) is beneficial to improve efficacy and reduce adverse reactions of linezolid.

CYP2C19 and CYP2J2 genotypes predict praziquantel plasma exposure among Ethiopian school-aged children

Metabolism of praziquantel (PZQ), a racemic mixture and the only drug approved to treat S. mansoni infection, is mediated by genetically polymorphic enzymes. Periodic school-based mass drug administration (MDA) with PZQ is the core intervention to control schistosomiasis. However data on the impact of pharmacogenetic variation, nutrition, and infection status on plasma PZQ exposure is scarce. We investigated genetic and non-genetic factors influencing PZQ plasma concentration and its metabolic ratios (trans-4-OH-PZQ/PZQ and cis-4-OH-PZQ/PZQ). Four hundred forty-six school children aged 7-15 years from four primary schools in southern Ethiopia who received albendazole and PZQ preventive chemotherapy through MDA campaign were enrolled. Genotyping for common functional variants of CYP3A4 (*1B), CYP3A5 (*3, *6), CYP2C19 (*2, *3, *17), CYP2C9 (*2, *3), and CYP2J2*7 was performed. Plasma concentrations of PZQ, trans-4-OH-PZQ, and cis-4-OH-PZQ were quantified using UPLCMS/MS. Carriers of CYP2C19 defective variant alleles (*2 and *3) had significantly higher mean PZQ plasma concentration than CYP2C19*1/*1 or *17 carriers (p = 0.005). CYP2C19*1/*1 and CYP2C19*17 carriers had higher trans-4-OH-PZQ/PZQ and cis-4-OH-PZQ/PZQ metabolic ratios compared with CYP2C19*2 or *3 carriers (p < 0.001). CYP2J2*7 carriers had lower mean PZQ plasma concentration (p = 0.05) and higher trans-4-OH-PZQ/PZQ and cis-4-OH-PZQ/PZQ metabolic ratios. Male participants had significantly higher PZQ concentration (p = 0.006) and lower metabolic ratios (p = 0.001) than females. There was no significant effect of stunting, wasting, S. mansoni or soil-transmitted helminth infections, CYP3A4, CYP3A5, or CYP2C9 genotypes on plasma PZQ or its metabolic ratios. In conclusion, sex, CYP2C19 and CYP2J2 genotypes significantly predict PZQ plasma exposure among Ethiopian children. The impact of CYP2C19 and CYP2J2 genotypes on praziquantel treatment outcomes requires further investigation.

Assessing potential drug-drug interactions between clofazimine and other frequently used agents to treat drug-resistant tuberculosis

Clofazimine is included in drug regimens to treat rifampicin/drug-resistant tuberculosis (DR-TB), but there is little information about its interaction with other drugs in DR-TB regimens. We evaluated the pharmacokinetic interaction between clofazimine and isoniazid, linezolid, levofloxacin, and cycloserine, dosed as terizidone. Newly diagnosed adults with DR-TB at Klerksdorp/Tshepong Hospital, South Africa, were started on the then-standard treatment with clofazimine temporarily excluded for the initial 2 weeks. Pharmacokinetic sampling was done immediately before and 3 weeks after starting clofazimine, and drug concentrations were determined using validated liquid chromatography-tandem mass spectrometry assays. The data were interpreted with population pharmacokinetics in NONMEM v7.5.1 to explore the impact of clofazimine co-administration and other relevant covariates on the pharmacokinetics of isoniazid, linezolid, levofloxacin, and cycloserine. Clofazimine, isoniazid, linezolid, levofloxacin, and cycloserine data were available for 16, 27, 21, 21, and 6 participants, respectively. The median age and weight for the full cohort were 39 years and 52 kg, respectively. Clofazimine exposures were in the expected range, and its addition to the regimen did not significantly affect the pharmacokinetics of the other drugs except levofloxacin, for which it caused a 15% reduction in clearance. A posteriori power size calculations predicted that our sample sizes had 97%, 90%, and 87% power at P < 0.05 to detect a 30% change in clearance of isoniazid, linezolid, and cycloserine, respectively. Although clofazimine increased the area under the curve of levofloxacin by 19%, this is unlikely to be of great clinical significance, and the lack of interaction with other drugs tested is reassuring.

DeepP450: Predicting Human P450 Activities of Small Molecules by Integrating Pretrained Protein Language Model and Molecular Representation

Cytochrome P450 enzymes (CYPs) play a crucial role in Phase I drug metabolism in the human body, and CYP activity toward compounds can significantly affect druggability, making early prediction of CYP activity and substrate identification essential for therapeutic development. Here, we established a deep learning model for assessing potential CYP substrates, DeepP450, by fine-tuning protein and molecule pretrained models through feature integration with cross-attention and self-attention layers. This model exhibited high prediction accuracy (0.92) on the test set, with area under the receiver operating characteristic curve (AUROC) values ranging from 0.89 to 0.98 in substrate/nonsubstrate predictions across the nine major human CYPs, surpassing current benchmarks for CYP activity prediction. Notably, DeepP450 uses only one model to predict substrates/nonsubstrates for any of the nine CYPs and exhibits certain generalizability on novel compounds and different categories of human CYPs, which could greatly facilitate early stage drug design by avoiding CYP-reactive compounds.

Utility of Cytochrome P450 4F2 Genotyping to Assess Drug Interaction Risk for Brincidovovir, a Cytochrome P450 4F2 Substrate

Smallpox was eradicated in 1980 but remains a biothreat due to the potential release of variola virus into the general population. Brincidofovir, the second medicine approved by the US Food and Drug Administration to treat smallpox, is metabolized by oxidative and hydrolytic pathways. The oxidative pathway is initiated by cytochrome P450 4F2 (CYP4F2), an enzyme lacking clinical probes for drug interaction studies. The aim of this work was to assess the impact of reduced activity CYP4F2 variants (rs2108622, C/T and T/T) on brincidofovir pharmacokinetics as a surrogate for drug inhibition. Genotyping was performed on blood from healthy participants receiving oral (n = 261) and intravenous (IV, n = 49) brincidofovir across 6 phase 1 trials. Plasma concentrations were measured by validated liquid chromatography tandem mass spectrometry methods. After oral administration, subjects with the lowest activity CYP4F2 genotype (T/T) had up to 36% higher AUCinf and 29% higher Cmax while subjects with the moderate activity CYP4F2 genotype (C/T) had similar Cmax and AUCinf compared to those with the wild-type genotype. Little to no increase in brincidofovir exposure parameters was observed following IV administration. Based on the lack of significant increases in brincidofovir plasma concentrations in subjects with low activity CYP4F2, a clinically meaningful drug-drug interaction is not expected with CYP4F2 inhibitor and brincidofovir coadministration.

Investigating the association between CYP2J2 inhibitors and QT prolongation: a literature review

Drug withdrawal post-marketing due to cardiotoxicity is a major concern for drug developers, regulatory agencies, and patients. One common mechanism of cardiotoxicity is through inhibition of cardiac ion channels, leading to prolongation of the QT interval and sometimes fatal arrythmias. Recently, oxylipin signaling compounds have been shown to bind to and alter ion channel function, and disruption in their cardiac levels may contribute to QT prolongation. Cytochrome P450 2J2 (CYP2J2) is the predominant CYP isoform expressed in cardiomyocytes, where it oxidizes arachidonic acid to cardioprotective epoxyeicosatrienoic acids (EETs). In addition to roles in vasodilation and angiogenesis, EETs bind to and activate various ion channels. CYP2J2 inhibition can lower EET levels and decrease their ability to preserve cardiac rhythm. In this review, we investigated the ability of known CYP inhibitors to cause QT prolongation using Certara's Drug Interaction Database. We discovered that among the multiple CYP isozymes, CYP2J2 inhibitors were more likely to also be QT-prolonging drugs (by approximately 2-fold). We explored potential binding interactions between these inhibitors and CYP2J2 using molecular docking and identified four amino acid residues (Phe61, Ala223, Asn231, and Leu402) predicted to interact with QT-prolonging drugs. The four residues are located near the opening of egress channel 2, highlighting the potential importance of this channel in CYP2J2 binding and inhibition. These findings suggest that if a drug inhibits CYP2J2 and interacts with one of these four residues, then it may have a higher risk of QT prolongation and more preclinical studies are warranted to assess cardiovascular safety.

A Review of CYP-Mediated Drug Interactions: Mechanisms and In Vitro Drug-Drug Interaction Assessment

Drug metabolism is a major determinant of drug concentrations in the body. Drug-drug interactions (DDIs) caused by the co-administration of multiple drugs can lead to alteration in the exposure of the victim drug, raising safety or effectiveness concerns. Assessment of the DDI potential starts with in vitro experiments to determine kinetic parameters and identify risks associated with the use of comedication that can inform future clinical studies. The diverse range of experimental models and techniques has significantly contributed to the examination of potential DDIs. Cytochrome P450 (CYP) enzymes are responsible for the biotransformation of many drugs on the market, making them frequently implicated in drug metabolism and DDIs. Consequently, there has been a growing focus on the assessment of DDI risk for CYPs. This review article provides mechanistic insights underlying CYP inhibition/induction and an overview of the in vitro assessment of CYP-mediated DDIs.

The Importance of Tracking "Missing" Metabolites: How and Why?

Technologies currently employed to find and identify drug metabolites in complex biological matrices generally yield results that offer a comprehensive picture of the drug metabolite profile. However, drug metabolites can be missed or are captured only late in the drug development process. This could be due to a variety of factors, such as metabolism that results in partial loss of the molecule, covalent bonding to macromolecules, the drug being metabolized in specific human tissues, or poor ionization in a mass spectrometer. These scenarios often draw a great deal of attention from chemistry, safety assessment, and pharmacology. This review will summarize scenarios of missing metabolites, why they are missing, and associated uncovering strategies from deeper investigations. Uncovering previously missed metabolites can have ramifications in drug development with toxicological and pharmacological consequences, and knowledge of these can help in the design of new drugs.

Rifampicin reduces plasma concentration of linezolid in patients with infective endocarditis

BACKGROUND

Linezolid in combination with rifampicin has been used in treatment of infective endocarditis especially for patients infected with staphylococci.

OBJECTIVES

Because rifampicin has been reported to reduce the plasma concentration of linezolid, the present study aimed to characterize the population pharmacokinetics of linezolid for the purpose of quantifying an effect of rifampicin cotreatment. In addition, the possibility of compensation by dosage adjustments was evaluated.

PATIENTS AND METHODS

Pharmacokinetic measurements were performed in 62 patients treated with linezolid for left-sided infective endocarditis in the Partial Oral Endocarditis Treatment (POET) trial. Fifteen patients were cotreated with rifampicin. A total of 437 linezolid plasma concentrations were obtained. The pharmacokinetic data were adequately described by a one-compartment model with first-order absorption and first-order elimination.

RESULTS

We demonstrated a substantial increase of linezolid clearance by 150% (95% CI: 78%-251%), when combined with rifampicin. The final model was evaluated by goodness-of-fit plots showing an acceptable fit, and a visual predictive check validated the model. Model-based dosing simulations showed that rifampicin cotreatment decreased the PTA of linezolid from 94.3% to 34.9% and from 52.7% to 3.5% for MICs of 2 mg/L and 4 mg/L, respectively.

CONCLUSIONS

A substantial interaction between linezolid and rifampicin was detected in patients with infective endocarditis, and the interaction was stronger than previously reported. Model-based simulations showed that increasing the linezolid dose might compensate without increasing the risk of adverse effects to the same degree.

Acute-on-chronic liver failure alters linezolid pharmacokinetics in critically ill patients with continuous hemodialysis: an observational study

BACKGROUND

In acute-on-chronic liver failure (ACLF), adequate antibiotic dosing is challenging due to changes of drug distribution and elimination. We studied the pharmacokinetics of linezolid in critically ill patients with ACLF during continuous renal replacement therapy compared to patients without concomitant liver failure (NLF).

METHODS

In this prospective cohort study, patients received linezolid 600 mg bid. Linezolid serum samples were analyzed by high-performance liquid chromatography. Population pharmacokinetic modelling was performed followed by Monte-Carlo simulations of 150 mg bid, 300 mg bid, 450 mg bid, 600 mg bid, and 900 mg bid to assess trough concentration target attainment of 2-7 mg/L.

RESULTS

Eighteen patients were included in this study with nine suffering from ACLF. Linezolid body clearance was lower in the ACLF group with mean (standard deviation) 1.54 (0.52) L/h versus 6.26 (2.43) L/h for NLF, P < 0.001. A trough concentration of 2-7 mg/L was reached with the standard dose of 600 mg bid in the NLF group in 47%, with 42% being underexposed and 11% overexposed versus 20% in the ACLF group with 77% overexposed and 3% underexposed. The highest probability of target exposure was attained with 600 mg bid in the NLF group and 150 mg bid in the ACLF group with 53%.

CONCLUSION

Linezolid body clearance in ACLF was markedly lower than in NLF. Given the overall high variability, therapeutic drug monitoring (TDM) with dose adjustments seems required to optimize target attainment. Until TDM results are available, a dose reduction may be considered in ACLF patients to prevent overexposure.

Pharmacokinetics of Antibacterial Agents in the Elderly: The Body of Evidence

Infections are important factors contributing to the morbidity and mortality among elderly patients. High rates of consumption of antimicrobial agents by the elderly may result in increased risk of toxic reactions, deteriorating functions of various organs and systems and leading to the prolongation of hospital stay, admission to the intensive care unit, disability, and lethal outcome. Both safety and efficacy of antibiotics are determined by the values of their plasma concentrations, widely affected by physiologic and pathologic age-related changes specific for the elderly population. Drug absorption, distribution, metabolism, and excretion are altered in different extents depending on functional and morphological changes in the cardiovascular system, gastrointestinal tract, liver, and kidneys. Water and fat content, skeletal muscle mass, nutritional status, use of concomitant drugs are other determinants of pharmacokinetics changes observed in the elderly. The choice of a proper dosing regimen is essential to provide effective and safe antibiotic therapy in terms of attainment of certain pharmacodynamic targets. The objective of this review is to perform a structure of evidence on the age-related changes contributing to the alteration of pharmacokinetic parameters in the elderly.

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Human Cytochrome P450 1, 2, 3 Families as Pharmacogenes with Emphases on Their Antimalarial and Antituberculosis Drugs and Prevalent African Alleles

Precision medicine gives individuals tailored medical treatment, with the genotype determining the therapeutic strategy, the appropriate dosage, and the likelihood of benefit or toxicity. Cytochrome P450 (CYP) enzyme families 1, 2, and 3 play a pivotal role in eliminating most drugs. Factors that affect CYP function and expression have a major impact on treatment outcomes. Therefore, polymorphisms of these enzymes result in alleles with diverse enzymatic activity and drug metabolism phenotypes. Africa has the highest CYP genetic diversity and also the highest burden of malaria and tuberculosis, and this review presents current general information on CYP enzymes together with variation data concerning antimalarial and antituberculosis drugs, while focusing on the first three CYP families. Afrocentric alleles such as CYP2A6*17, CYP2A6*23, CYP2A6*25, CYP2A6*28, CYP2B6*6, CYP2B6*18, CYP2C8*2, CYP2C9*5, CYP2C9*8, CYP2C9*9, CYP2C19*9, CYP2C19*13, CYP2C19*15, CYP2D6*2, CYP2D6*17, CYP2D6*29, and CYP3A4*15 are implicated in diverse metabolic phenotypes of different antimalarials such as artesunate, mefloquine, quinine, primaquine, and chloroquine. Moreover, CYP3A4, CYP1A1, CYP2C8, CYP2C18, CYP2C19, CYP2J2, and CYP1B1 are implicated in the metabolism of some second-line antituberculosis drugs such as bedaquiline and linezolid. Drug-drug interactions, induction/inhibition, and enzyme polymorphisms that influence the metabolism of antituberculosis, antimalarial, and other drugs, are explored. Moreover, a mapping of Afrocentric missense mutations to CYP structures and a documentation of their known effects provided structural insights, as understanding the mechanism of action of these enzymes and how the different alleles influence enzyme function is invaluable to the advancement of precision medicine.

Pharmacokinetic analysis of linezolid for multidrug resistant tuberculosis at a tertiary care centre in Mumbai, India

Linezolid is an oxazolidinone used to treat multidrug-resistant tuberculosis (MDR-TB), including in the recently-endorsed shorter 6-month treatment regimens. Due to its narrow therapeutic index, linezolid is often either dose-adjusted or discontinued due to intolerance or toxicity during treatment, and the optimal balance between linezolid efficacy and toxicity remains unclear. India carries a significant burden of MDR-TB cases in the world, but limited information on the pharmacokinetics of linezolid and minimum inhibitory concentration (MIC) distribution is available from Indian MDR-TB patients. We enrolled participants from a tertiary care centre in Mumbai, India, treated for MDR-TB and receiving linezolid daily doses of 600 or 300 mg. Pharmacokinetic visits were scheduled between 1 and 15 months after treatment initiation to undergo intensive or sparse blood sampling. Linezolid concentration versus time data were analysed using non-linear mixed-effects modelling, with simulations to evaluate doses for different scenarios. We enrolled 183 participants (121 females), with a median age of 26 years (interquartile range [IQR] 21-35), weight 55.0 kg (IQR 45.6-65.8), and fat-free mass 38.7 kg (IQR 32.7-46.0). Linezolid pharmacokinetics was best described by a one-compartment model with first-order elimination allometrically scaled by fat-free mass and transit compartment absorption. The typical clearance value was 3.81 L/h. Simulations predicted that treatment with 300 mg daily achieves a high probability of target attainment (PTA) when linezolid MIC was ≤0.25 mg/L (61.5% of participant samples tested), while 600 mg daily would be required if MIC were 0.5 mg/L (29% of samples). While linezolid 300 mg daily is predicted to achieve effective targets for the majority of adults with MDR-TB, it failed to achieve the therapeutic target for 21% participants. A dose of 600 mg had a PTA >90% for all susceptible samples, but with a higher likelihood of exceeding toxicity thresholds (31% vs 9.6%). These data suggest potential benefit to individualized dosing taking host and microbial characteristics into account to improve the likelihood of treatment efficacy while minimizing risk of toxicity from linezolid for the treatment of MDR-TB. Further prospective evaluation in different clinical settings is urgently needed to inform safety and efficacy of these lower doses.

A standard dose of linezolid puts patients with hepatic impairment at risk of overexposure

PURPOSE

The purpose of this retrospective observational study conducted in patients with hepatic impairment was to assess the variability of linezolid trough concentrations, to determine the risk factors for linezolid overexposure, and to investigate the effect of linezolid overexposure on linezolid-induced thrombocytopenia.

METHODS

All enrolled patients received a standard dose (600 mg every 12 h) of linezolid and underwent therapeutic drug monitoring. The Child-Pugh-Turcotte score was used to divide patients into three groups: mild, moderate, and severe hepatic impairment. The risk factors for linezolid overexposure (C_min > 8 mg/L) and linezolid-induced thrombocytopenia were examined using logistic regression. And the Kaplan-Meier curve was used to describe the association between linezolid overexposure and linezolid-induced thrombocytopenia.

RESULTS

Seventy-seven patients were included, 37 (48.1%) of whom experienced linezolid overexposure. Patients with severe hepatic impairment had a substantially higher median C_min of linezolid than those with mild (20.7 mg/L vs 5.51 mg/L, P < 0.001) or moderate (20.7 mg/L vs 6.70 mg/L, P = 0.001) hepatic impairment. Severe hepatic impairment was significantly associated with linezolid overexposure (OR 7.037, 95%CI 1.426-34.727, P = 0.017). After linezolid treatment, linezolid-induced thrombocytopenia occurred in 32 (41.6%) patients, and C_min > 8 mg/L was a significant predictor of linezolid-induced thrombocytopenia (OR 3.024, 95%CI 1.083-8.541, P = 0.035).

CONCLUSION

Patients with hepatic impairment who received standard doses of linezolid are at greater risk of linezolid overexposure, which may lead to a higher incidence of linezolid-induced thrombocytopenia.

Species Specificity and Selection of Models for Drug Oxidations Mediated by Polymorphic Human Enzymes

Many drug oxygenations are mainly mediated by polymorphic cytochromes P450 (P450s) and also by flavin-containing monooxygenases (FMOs). More than 50 years of research on P450/FMO-mediated drug oxygenations have clarified their catalytic roles. The natural product coumarin causes hepatotoxicity in rats via the reactive coumarin 3,4-epoxide, a reaction catalyzed by P450 1A2; however, coumarin undergoes rapid 7-hydroxylation by polymorphic P450 2A6 in humans. The primary oxidation product of the teratogen thalidomide in rats is deactivated 5'-hydroxythalidomide plus sulfate and glucuronide conjugates; however, similar 5'-hydroxythalidomide and 5-hydroxythalidomide are formed in rabbits in vivo. Thalidomide causes human P450 3A enzyme induction in liver (and placenta) and is also activated in vitro and in vivo by P450 3A through the primary human metabolite 5-hydroxythalidomide (leading to conjugation with glutathione/nonspecific proteins). Species differences exist in terms of drug metabolism in rodents and humans, and such differences can be very important when determining the contributions of individual enzymes. The approaches used for investigating the roles of human P450 and FMO enzymes in understanding drug oxidations and clinical therapy have not yet reached maturity and still require further development. SIGNIFICANCE STATEMENT: Drug oxidations in animals and humans mediated by P450s and FMOs are important for understanding the pharmacological properties of drugs, such as the species-dependent teratogenicity of the reactive metabolites of thalidomide and the metabolism of food-derived odorous trimethylamine to non-odorous (but proatherogenic) trimethylamine N-oxide. Recognized differences exist in terms of drug metabolism between rodents, non-human primates, and humans, and such differences are important when determining individual liver enzyme contributions with substrates in in vitro and in vivo systems.

Bioequivalence of Two Linezolid Tablets Under Fed and Fasting Conditions in Healthy Chinese Individuals

Linezolid, an oxazolidinone antibacterial agent with several formulations, has been widely used for over 20 years. This study aimed to compare the bioequivalence, pharmacokinetics, and safety of test and reference linezolid tablets after a single oral dose under fasting/fed conditions. In this open-label, randomized, two-period, crossover, bioequivalence study, 48 healthy volunteers were enrolled equally to fasting or fed groups to receive one 600-mg test or reference linezolid tablet in each period. Pharmacokinetic parameters were calculated using noncompartmental methods. Adverse events (AEs) were recorded to assess safety. The geometric mean terminal half-lives of test and reference formulations were 3.8 and 3.6 hours, respectively, under both fasting and fed conditions. The median time to reach the maximum observed concentration was 1.0 hour (both formulations) in the fasting group, and 2.0 hours (test formulation) and 2.5 hours (reference formulation) in the fed group. No substantial differences were observed in the area under plasma concentration-time curve (AUC) from time 0 to the last sampling time (AUC_0-t ) and the maximum observed concentration (C_max ) between formulations. Geometric least square mean ratios for C_max , AUC_0-t , and AUC from time 0 to infinity were approximately 100%, and the corresponding 90% confidence intervals for bioequivalence were within 80%-125%. Ten participants reported 11 AEs; AEs were mild, except for one pregnancy event with an outcome of induced absorption. Bioequivalence between the two linezolid formulations was demonstrated under fasting and fed conditions, and a similar safety profile was observed among healthy Chinese volunteers.

Linezolid Exposure Is Associated with Cytopenias in Patients Treated for Multidrug-Resistant Tuberculosis

Although linezolid is effective for multidrug-resistant TB (MDR-TB) tuberculosis treatment, it is associated with cytopenias after 4 weeks of administration. Data on toxicities with long-term use of linezolid and drug pharmacodynamics in MDR-TB treatment are limited, and concerns about toxicity present barriers to wider implementation. This was a secondary analysis of a prospective cohort study of patients treated for MDR-TB in the country of Georgia from 2015 to 2017. Intensive blood sampling 4 to 6 weeks after treatment initiation with linezolid 600 mg daily was performed for pharmacokinetic (PK) analysis, including linezolid trough concentration (Cmin) and area under the curve from 0 to 24 hours (AUC0-24). Linezolid exposure was defined using literature-reported thresholds. Cytopenias were defined using an NIH adverse event (AE) scale. Logistic regression was used to evaluate the relationship between linezolid exposure and cytopenias. Among 76 patients receiving linezolid in their baseline treatment regimen and who had PK data available, cytopenia AEs occurred in 30 (39.5%) for an incidence rate of 46 per 100 person-years. The median duration of linezolid therapy was 526 days. No patients required dose reduction or interruption due to cytopenias. Median linezolid Cmin was 0.235 mg/L (interquartile range [IQR], 0.069 to 0.529), and median AUC0-24 was 89.6 mg·h/L (IQR, 69.2 to 116.2). Cytopenias were associated with linezolid PK parameters (Cmin > 2 mg/L and AUC0-24 > 160 mg·h/L). Cytopenias occurred frequently with long-term use of linezolid 600 mg/day and were associated with PK parameters but did not result in the need for treatment interruption in the management of a cohort of patients with MDR-TB.

Plasma and synovial fluid concentrations of linezolid in patients with knee osteoarthritis infected with Staphylococcus aureus

Background

Linezolid is a new oxazolidinone antibiotic used for infections caused by methicillin-resistant Staphylococcus and other species.

Case presentation

Two cases of knee osteoarthritis with acute infection were successfully treated using linezolid. The plasma and synovial fluid concentrations of linezolid in two patients [women aged 69 and 73 years (cases 1 and 2)] with knee osteoarthritis infected with Staphylococcus aureus were measured after they were administered 600 mg twice daily by intravenous infusion. The plasma linezolid concentrations during knee surgery in case 1 at day 5 and in case 2 at day 2 were 19.6 and 15.6 μg/mL, respectively. The synovial fluid concentrations of linezolid in samples taken during surgery in case 1 and case 2 were 14.9 and 17.0 μg/mL, respectively; these values corresponded to ratios of synovial fluid/plasma of 76 and 109%. Possible metabolite 2-hydroxylated linezolid potentially mediated by cytochrome P450 2 J2 was not detected in the plasma or synovial fluid samples under the current clinical setting after multiple doses.

Conclusions

These results implied nearly equivalent concentrations of linezolid in plasma and synovial fluid of clinical patients with knee osteoarthritis acutely infected with Staphylococcus aureus.