Inhibitory Effect of Antituberculosis Drugs on Human Cytochrome P450-Mediated Activities

Polymorphism of CYP3A4*18 is associated with anti-tuberculosis drug-induced hepatotoxicity

Aim: The association between cytochrome P450 (CYP) gene polymorphisms and anti-tuberculosis drug-induced hepatotoxicity (ATDH) was investigated in patients with or without pre-existing liver diseases (PLD). Materials & methods: We followed 164 tuberculosis subjects, 58 with PLD and 106 without PLD. Polymorphisms in CYP2D6, CYP2C9, CYP2C19, CYP3A4 and CYP3A5 were analyzed using the TaqMan® SNP genotyping assay. Results: The CYP3A4*18 heterozygous genotype was associated with ATDH (OR: 3.24, 95% CI: 1.06-9.86) regardless of PLD presence. Among subjects without PLD, CYP3A4*18 heterozygotes had significantly higher ATDH risk (OR: 9.10, 95% CI: 1.56-53.16). Conversely, in the PLD group, CYP3A4*18 heterozygotes had lower ATDH risk (OR: 0.21, 95% CI: 0.05-0.98). Conclusion: CYP3A4*18 genotype is linked to ATDH in tuberculosis patients, with differential effects based on PLD presence.

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.

The first-line antituberculosis drugs, and their fixed-dose combination induced abnormal sperm morphology and histological lesions in the testicular cells of male mice

Rifampicin (RIF), Isoniazid (INH), Ethambutol (EMB), Pyrazinamide (PZA), and/or their fixed-dose combination (FDC) are extensively prescribed in the cure of Tuberculosis (TB) globally. In spite of the beneficial effect, these drugs are capable of inducing cellular toxicity. Existing information on the genotoxic effects of the first-line anti-TB drugs is limited and contentious. Herein, we evaluated the reproductive genotoxicity of RIF, INH, EMB, PZA, and their FDC utilizing the mouse sperm morphology assay. Histological examination of the testes of exposed mice was also performed. Male Swiss albino mice (11-13 weeks old) were intraperitoneally exposed for 5 consecutive days to each of the anti-TB drugs at four different doses of 6.25, 12.5, 25, and 50 mg/kg bw of PZA; 2.5, 5.0, 10, and 20 mg/kg bw of RIF; 1.25, 2.5, 5.0 and 10 mg/kg bw of INH; 3.75, 7.5, 15 and 30 mg/kg bw of EMB; and 7, 14, 28 and 56 mg/kg bw of FDC corresponding respectively to ×0.25, ×0.5, ×1 and ×2.0 of the standard daily dose. In comparison with the negative control (normal saline), there was no significant difference in the testicular weight and organo-somatic index of exposed mice. There was an increase (p > 0.05) in the frequency of abnormal spermatozoa at most of the tested doses of each drug and a dose-dependent decrease with the FDC. Each of the anti-TB drugs except the FDC induced pathological lesions in the testes. These findings suggest that the individual first-line anti-TB drug unlike the FDC has the potential to provoke testicular anomalies in male mice.

A Literature Review of Liver Function Test Elevations in Rifampin Drug-Drug Interaction Studies

Although rifampin drug–drug interaction (DDI) studies are routinely conducted, there have been instances of liver function test (LFT) elevations, warranting further evaluation. A literature review was conducted to identify studies in which combination with rifampin resulted in hepatic events and evaluate any similarities. Over 600 abstracts and manuscripts describing rifampin DDI studies were first evaluated, of which 30 clinical studies reported LFT elevations. Out of these, 11 studies included ritonavir in combination with other drug(s) in the rifampin DDI study. The number of subjects that were discontinued from treatment on these studies ranged from 0 to 71 (0–100% of subjects in each study). The number of subjects hospitalized for adverse events in these studies ranged from 0 to 41 (0–83.67% of subjects in each study). LFT elevations in greater than 50% of subjects were noted during the concomitant administration of rifampin with ritonavir‐boosted protease inhibitors and with lorlatinib; with labeled contraindication due to observed hepatotoxicity related safety findings only for saquinavir/ritonavir and lorlatinib. In the lorlatinib and ritonavir DDI studies, considerable LFT elevations were observed rapidly, typically within 24–72 h following co‐administration. A possible sequence effect has been speculated, where rifampin induction prior to administration of the combination may be associated with increased severity of the LFT elevations. The potential role of rifampin in the metabolic activation of certain drugs into metabolites with hepatic effects needs to be taken into consideration when conducting rifampin DDI studies, particularly those for which the metabolic profiles are not fully elucidated.

Inhibition of CYP3A-mediated Midazolam Metabolism by <i>Kaempferia Parviflora</i>

Kaempferia parviflora (KP) extract has recently attracted attention in Japan as a dietary supplement; however, there is little information regarding food-drug interactions (FDIs). The current study was conducted to clarify the FDI of KP extract via inhibition of cytochrome P450 3A (CYP3A), a typical drug-metabolizing enzyme. The inhibitory effects of KP extract and its main ingredients, 5,7-dimethoxyflavone (5,7-DMF) and 3,5,7,3’,4’-pentamethoxyflavone (3,5,7,3’,4’-PMF), on CYP3A-mediated midazolam 1’-hydroxylation (MDZ 1’-OH) activity were investigated in human liver microsomes. In addition, the effect of a single oral treatment with KP extract (135 mg/kg) on oral MDZ (15 mg/kg) metabolism was investigated in rats. Serum MDZ concentration was analyzed and pharmacokinetic parameters were compared with the control group. KP extract competitively inhibited MDZ 1’-OH activity with an inhibition constant value of 78.14 µg/ml, which was lower than the estimated concentration in the small intestine after ingestion. Furthermore, KP extract, 5,7-DMF, and 3,5,7,3’,4’-PMF inhibited the activity in a time-, NADPH-, and concentration-dependent manner. In vivo study showed that administration of KP extract to rats 2 h before MDZ significantly increased the area under the serum concentration-time curve and the maximum concentration of MDZ significantly by 2.3- and 1.9- fold, respectively (p < 0.05). Conversely, administration of MDZ 18 h after KP extract treatment displayed a weaker effect. These results suggest that KP extract competitively inhibits CYP3A-mediated MDZ metabolism, and that this inhibition may be time-dependent but not irreversible. This work suggests an FDI through CYP3A inhibition by KP extract.

Integration of Clinical and Scientific Principles in the Teaching of Drug-Drug Interactions

Evaluation of drug-drug interactions (DDIs) is an integral part of pharmacy practice worldwide. An understanding of the scientific mechanisms behind and the clinical implications of DDIs is important for proper management of pharmacotherapy. Here, we describe an integrated approach to teaching both aspects of DDIs as a standalone module in diverse course settings. These include on-campus and online delivery to international and local audiences in small and large classes. We describe the scientific, clinical, and integrated learning objectives of the module, and we show how these can be achieved through group projects based on published DDI case reports.

Prediction of potential drug interactions between repurposed COVID-19 and antitubercular drugs: an integrational approach of drug information software and computational techniques data

Introduction:

Tuberculosis is a major respiratory disease globally with a higher prevalence in Asian and African countries than rest of the world. With a larger population of tuberculosis patients anticipated to be co-infected with COVID-19 infection, an ongoing pandemic, identifying, preventing and managing drug–drug interactions is inevitable for maximizing patient benefits for the current repurposed COVID-19 and antitubercular drugs.

Methods:

We assessed the potential drug–drug interactions between repurposed COVID-19 drugs and antitubercular drugs using the drug interaction checker of IBM Micromedex®. Extensive computational studies were performed at a molecular level to validate and understand the drug–drug interactions found from the Micromedex drug interaction checker database at a molecular level. The integrated knowledge derived from Micromedex and computational data was collated and curated for predicting potential drug–drug interactions between repurposed COVID-19 and antitubercular drugs.

Results:

A total of 91 potential drug–drug interactions along with their severity and level of documentation were identified from Micromedex between repurposed COVID-19 drugs and antitubercular drugs. We identified 47 pharmacodynamic, 42 pharmacokinetic and 2 unknown DDIs. The majority of our molecular modelling results were in line with drug–drug interaction data obtained from the drug information software. QT prolongation was identified as the most common type of pharmacodynamic drug–drug interaction, whereas drug–drug interactions associated with cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp) inhibition and induction were identified as the frequent pharmacokinetic drug–drug interactions. The results suggest antitubercular drugs, particularly rifampin and second-line agents, warrant high alert and monitoring while prescribing with the repurposed COVID-19 drugs.

Conclusion:

Predicting these potential drug–drug interactions, particularly related to CYP3A4, P-gp and the human Ether-à-go-go-Related Gene proteins, could be used in clinical settings for screening and management of drug–drug interactions for delivering safer chemotherapeutic tuberculosis and COVID-19 care. The current study provides an initial propulsion for further well-designed pharmacokinetic-pharmacodynamic-based drug–drug interaction studies.

Plain Language Summary

Current challenges and future perspectives in oral absorption research: An opinion of the UNGAP network

Although oral drug delivery is the preferred administration route and has been used for centuries, modern drug discovery and development pipelines challenge conventional formulation approaches and highlight the insufficient mechanistic understanding of processes critical to oral drug absorption. This review presents the opinion of UNGAP scientists on four key themes across the oral absorption landscape: (1) specific patient populations, (2) regional differences in the gastrointestinal tract, (3) advanced formulations and (4) food-drug interactions. The differences of oral absorption in pediatric and geriatric populations, the specific issues in colonic absorption, the formulation approaches for poorly water-soluble (small molecules) and poorly permeable (peptides, RNA etc.) drugs, as well as the vast realm of food effects, are some of the topics discussed in detail. The identified controversies and gaps in the current understanding of gastrointestinal absorption-related processes are used to create a roadmap for the future of oral drug absorption research.

Clinical Pharmacokinetics of the Novel HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitor Doravirine: An Assessment of the Effect of Patient Characteristics and Drug-Drug Interactions

Doravirine (MK-1439) is a novel non-nucleoside reverse transcriptase inhibitor indicated for the combination treatment of human immunodeficiency virus type-1 (HIV-1) infection. The recommended dose is 100 mg once daily. This review summarizes the pharmacokinetics of doravirine, the influence of intrinsic factors, and its drug-drug interaction (DDI) profile. Following oral administration, doravirine is rapidly absorbed (median time to maximum plasma concentration, 1-4 h) and undergoes cytochrome P450 (CYP)3A-mediated oxidative metabolism. Steady-state geometric means for AUC0-24, C24, and Cmax in individuals with HIV-1 following administration of doravirine 100 mg once daily are 37.8 μM·h, 930 nM, and 2260 nM, respectively. Age, gender, severe renal impairment, and moderate hepatic impairment have no clinically meaningful effect on doravirine pharmacokinetics, and there is limited potential for DDIs. No dose adjustment is necessary when doravirine is co-administered with strong CYP3A inhibitors. However, doravirine is contraindicated with strong CYP3A inducers (e.g., rifampin), and dose adjustment of doravirine is recommended for co-administration with the moderate CYP3A inducer, rifabutin. Included in this review are clinical trial data from phase I pharmacokinetic trials, including DDI trials and trials in participants with renal and hepatic disease but without HIV-1 infection (N = 326), as well as phase I, II, and III safety and efficacy trials in participants living with HIV-1 (N = 991). Based on these data, the pharmacokinetic profile of doravirine supports its use in diverse populations living with HIV-1 and allows co-administration with various antiretroviral agents and treatments for commonly occurring co-morbidities.

Population Pharmacokinetics and Pharmacogenetics of Ethambutol in Adult Patients Coinfected with Tuberculosis and HIV

This study aimed to characterize the population pharmacokinetics and pharmacogenetics of ethambutol in tuberculosis-HIV-coinfected adult patients. Ethambutol plasma concentrations, determined by liquid chromatography-tandem mass spectrometry, in 63 patients receiving ethambutol as part of rifampin-based fixed-dose combination therapy for tuberculosis were analyzed using nonlinear mixed-effects modeling. A one-compartment disposition model with first-order elimination and four transit compartments prior to first-order absorption was found to adequately describe the concentration-time profiles of ethambutol in plasma. Body weight was implemented as an allometric function on the clearance and volume parameters. Estimates of oral clearance and volume of distribution were 77.4 liters/h and 76.2 liters, respectively. A G/A mutation with regard to CYP1A2 2159 G>A was associated with a 50% reduction in relative bioavailability. Simulations revealed that doses of 30 mg/kg of body weight and 50 mg/kg for G/G and G/A carriers, respectively, would result in clinically adequate exposure. The results presented here suggest that CYP1A2 polymorphism affects ethambutol exposure in this population and that current treatment guidelines may result in underexposure in patients coinfected with tuberculosis and HIV. Based on simulations, a dose increase from15 to 20 mg/kg to 30 mg/kg is suggested. However, the 50-mg/kg dose required to reach therapeutic exposure in G/A carriers may be inappropriate due to the dose-dependent toxicity of ethambutol. Additional studies are required to further investigate CYP450 polymorphism effects on ethambutol pharmacokinetics.

Effect of Benifuuki Tea on Cytochrome P450-mediated Metabolic Activity in Rats

BACKGROUND/AIM

Benifuuki tea has recently been used as an alternative therapy for pollinosis, and it may be consumed with pharmaceutical drugs. This study aimed to examine cytochrome P450 (CYP)-mediated food-drug interactions with Benifuuki tea in rats.

MATERIALS AND METHODS

The inhibitory effects of Benifuuki tea and (-)-epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3"Me) on CYP activities were evaluated in vitro. Midazolam pharmacokinetics was investigated after two treatments with Benifuuki tea. In an ex vivo study, CYP activities were determined after 1-week-treatment with the tea.

RESULTS

Benifuuki tea and EGCG3"Me inhibited CYP2D and CYP3A activities in a concentration-dependent manner in vitro. However, MDZ metabolism did not change by Benifuuki treatment in vivo and ex vivo. In contrast, CYP2D activity was decreased ex vivo.

CONCLUSION

Normal intake of Benifuuki tea is not likely to cause food-drug interactions by CYP3A inhibition or induction. In contrast, Benifuuki tea consumption may lead to food-drug interactions through the inhibition of CYP2D.

Inhibitory Effect of Oxethazaine on Midazolam Metabolism in Rats

There have been few reports concerning to the drug-drug interactions (DDIs) with OTC drugs although an increase in the use of OTC drugs in recent years. This current study was conducted to clarify the DDIs through CYP3A inhibition by oxethazaine (OXZ), an antacid available as an OTC drug. Midazolam (MDZ) was used as a probe drug for CYP3A activity. In an in vivo study, a single oral dose of OXZ (50 mg/kg) was administered to rats 30, 60, or 120 min before oral MDZ administration (15 mg/kg). Serum concentrations of MDZ were analyzed by HPLC, and its pharmacokinetic parameters were compared with a water-treated control group. The inhibitory effect of OXZ on MDZ 1'-hydroxylation (MDZ 1'-OH) activity was investigated in vitro using rat liver and intestinal microsomes. Pretreatment of OXZ 120 min before MDZ administration significantly increased the area under the serum concentration-time curve (AUC_0-∞) of MDZ six-fold compared to the control group without a change in elimination half-life (t_1/2). In contrast, OXZ pretreatment 30 or 60 min before MDZ administration did not show any remarkable change in MDZ pharmacokinetic parameters. The in vitro study showed that OXZ inhibited MDZ 1'-OH activity in a concentration-dependent manner both in liver and intestinal microsomes. These results suggested that OXZ increases serum MDZ concentration presumably by the inhibition of liver and/or intestinal CYP3A activity. OXZ was predicted to cause the DDIs mediated by CYP3A inhibition, although this effect depended on the dose interval.

Evaluation of CYP2D6 Protein Expression and Activity in the Small Intestine to Determine Its Metabolic Capability in the Japanese Population

CYP2D6 plays an important role in the metabolism of many drugs such as opioids and antidepressants. Polymorphisms of the CYP2D6 gene are widely observed in the Japanese population, and can affect the first-pass metabolism of orally administered drugs. Several CYP enzymes have been identified in the small intestine of Caucasians, but intestinal CYP enzymes have not been reported in the Japanese population, except for CYP3A4 and CYP2C19. In this study, we evaluated the CYP2D6 metabolic capacity by measurement of CYP2D6 mRNA and protein levels and activity in the small intestine of Japanese individuals. Normal jejunal tissues were obtained from 31 patients who had undergone pancreaticoduodenectomy, and the CYP2D6*10 variant was identified in these tissues. CYP2D6 mRNA and CYP2D6 protein levels were analyzed using real-time RT-PCR and Western blotting, respectively. Bufuralol 1'-hydroxylation, a marker of CYP2D6 activity, was analyzed using HPLC. Frequencies of the CYP2D6*1/*1, *1/*10, and *10/*10 genotypes in the jejunal tissue were 29.0% (n=9), 35.5% (n=11), and 35.5% (n=11), respectively. CYP2D6 protein and activity levels did not differ significantly between the genotypes. A positive correlation was found between CYP2D6 protein and activity levels. Furthermore, CYP2D6 protein levels and activity in the small intestine were significantly lower than those in the liver. These findings suggest that the metabolic capacity of CYP2D6 in the small intestine of the Japanese population has a relatively small effect on drug metabolism.

Antiretroviral treatment in HIV-infected children who require a rifamycin-containing regimen for tuberculosis

INTRODUCTION

In high prevalence settings, tuberculosis and HIV dual infection and co-treatment is frequent. Rifamycins, especially rifampicin, in combination with isoniazid, ethambutol and pyrazinamide are key components of short-course antituberculosis therapy. Areas covered: We reviewed available data, for which articles were identified by a Pubmed search, on rifamycin-antiretroviral interactions in HIV-infected children. Rifamycins have potent inducing effects on phase I and II drug metabolising enzymes and transporters. Antiretroviral medications are often metabolised by the enzymes induced by rifamycins or may suppress specific enzyme activity leading to drug-drug interactions with rifamycins. These may cause significant alterations in their phamacokinetic and pharmacodynamic properties, and sometimes that of the rifamycin. Recommended strategies to adapt to these interactions include avoidance and dose adjustment. Expert opinion: Despite the importance and frequency of tuberculosis as an opportunistic disease in HIV-infected children, current data on the management of co-treated children is based on few studies. We need new strategies to rapidly assess the use of rifamycins, new anti-tuberculosis drugs and antiretroviral drugs together as information on safety and dosing of individual drugs becomes available.

Effect of antituberculosis treatment on CYP2C19 enzyme activity in genetically polymorphic South Indian Tamilian population

Patients on antituberculosis therapy (ATT) are more prone to drug interactions in the presence of coexisting illnesses which require drug therapy. Rifampicin is a pleiotropic inducer of CYP enzymes, and isoniazid is an enzyme inhibitor. Genetic variations are common in the gene coding for CYP2C19 enzyme. These variations would be important in predicting the individual variations in CYP2C19 activity. The objectives of the study were to find the net effect of 1-month ATT on CYP2C19 enzyme activity and its association with CYP2C19 genetic polymorphisms. Newly diagnosed tuberculosis patients (n = 125) were included in the study. Before commencing ATT, they were given a single dose of omeprazole 20 mg as a probe drug for CYP2C19. Blood sample was collected after 3 h to carry out phenotyping for CYP2C19 enzyme by measuring omeprazole hydroxylation index (OHI) using LC-MS/MS. The phenotyping procedure was repeated after 1 month of ATT. CYP2C19 genotyping was carried out by PCR-RFLP method. Significant reduction in OHI was observed after 1 month of ATT in all the metabolizer groups. The percentage reduction in OHI was maximum with poor metabolizers, 84.1 (IQR - 74.6, 86.6), and minimum with ultra-rapid metabolizers, 39.6 (IQR - 12.7, 54.7). CYP2C19 enzyme induction is predominant in patients after 1 month of antituberculosis treatment (ATT). Genetic variations in the enzyme could not clearly explain the interindividual differences in induction. There is a potential risk of drug failure/adverse effect in poor metabolizers regardless of their genotype after ATT.

Pharmacogenetics of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in resource-limited settings: Influence on antiretroviral therapy response and concomitant anti-tubercular, antimalarial and contraceptive treatments

The burden of human immunodeficiency virus (HIV) is mainly concentrated to resources-limited countries where the response to available antiretroviral therapy is often limited by the occurrence of toxicity or by the emergence of HIV drug resistance. Efavirenz and nevirapine are the antiretroviral drugs most prescribed in resources-limited countries as part of antiretroviral combination therapy. Their metabolism and conjugation are largely influenced by enzymatic genetic polymorphisms. The genetic variability of their metabolism could be associated to different metabolic phenotypes causing reduced patients' adherence because of toxicity or drug-drug interactions with concomitant therapies. The purpose of this review is to summarize published evidence on pharmacogenetic and pharmacokinetic aspects related to efavirenz and nevirapine, the influence of concomitant anti-tubercular, anti-malarial or contraceptive treatments, and the impact of human genetic variation and drug-drug interaction on the virologic and immunologic response to antiretroviral therapy in resources-limited countries.

CYP2B6*6, CYP2B6*18, Body weight and sex are predictors of efavirenz pharmacokinetics and treatment response: population pharmacokinetic modeling in an HIV/AIDS and TB cohort in Zimbabwe

Background

Efavirenz (EFV) therapeutic response and toxicity are associated with high inter-individual variability attributed to variation in its pharmacokinetics. Plasma concentrations below 1 μg/ml may result in virologic failure and above 4 μg/ml, may result in central nervous system adverse effects. This study used population pharmacokinetics modeling to explore the influence of demographic and pharmacogenetic factors including efavirenz-rifampicin interaction on EFV pharmacokinetics, towards safer dosing of EFV.

Methods

Patients receiving an EFV-based regimen for their antiretroviral therapy and a rifampicin-containing anti-TB regimen were recruited. EFV plasma concentrations were measured by HPLC and genomic DNA genotyped for variants in the CYP2B6, CYP2A6 and ABCB1 genes. All patients were evaluated for central nervous system adverse effects characterised as sleep disorders, hallucinations and headaches using the WHO ADR grading system. A pharmacokinetic model was built in a forward and reverse procedure using nonlinear mixed effect modeling in NONMEM VI followed by model-based simulations for optimal doses.

Results

CYP2B6*6 and *18 variant alleles, weight and sex were the most significant covariates explaining 55% of inter-individual variability in EFV clearance. Patients with the CYP2B6*6TT genotype had a 63% decrease in EFV clearance despite their CYP2B6*18 genotypes with females having 22% higher clearance compared to males. There was a 21% increase in clearance for every 10 kg increase in weight. The effect of TB/HIV co-treatment versus HIV treatment only was not statistically significant. No clinically relevant association between CYP2B6 genotypes and CNS adverse effects was seen, but patients with CNS adverse effects had a 27% lower clearance compared to those without. Model- based simulations indicated that all carriers of CYP2B6*6 TT genotype would be recommended a dose reduction to 200 mg/day, while the majority of extensive metabolisers may be given 400 mg/day and still maintain therapeutic levels.

Conclusion

This study showed that screening for CYP2B6 functional variants has a high predictability for efavirenz plasma levels and could be used in prescribing optimal and safe EFV doses.

Inhibition of cytochrome P450 by ethambutol in human liver microsomes

Although cytochrome P450 inhibition is the major drug-drug interaction (DDI) mechanism in clinical pharmacotherapy, DDI of a number of well-established drugs have not been investigated. Rifampicin, isoniazid, pyrazinamide and ethambutol combination therapy inhibits clearance of theophylline in patients with tuberculosis. We determined the inhibitory effects of ethambutol on the activities of nine CYP isoforms including CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4 in pooled human liver microsomes (HLM). As measured by liquid chromatography-electrospray ionization tandem mass spectrometry, ethambutol exhibited strong inhibitory potential against CYP1A2 and CYP2E1, moderate against CYP2C19 and CYP2D6 and weak against CYP2A6, CYP2C9 and CYP3A4, based on the IC50 values. The K(i) value of ethambutol for CYP1A2 was 1.4 μM and for CYP2E1 was 2.9 μM. Inhibition of CYP1A2 and CYP2E1 was not increased by preincubation with ethambutol and β-nicotinamideadenine dinucleotide phosphate (NADPH), suggesting that the ethambutol-induced CYP inhibition may not be metabolism-dependent. Kinetic analysis showed that the inhibition of CYP1A2 and CYP2E1 by ethambutol was best fit to a competitive inhibition model. Formation of 1-methylxanthene and 1,3-dimethyluric acid from theophylline in HLM was decreased to 47% and 36%, respectively, by 3.0 μM ethambutol, which is comparable to its IC50 value against CYP1A2. Considering its maximal plasma concentrations of ~10 μM and long half-life of ~22 h, our findings raise the possibility that ethambutol causes significant DDIs in clinical situations with drugs with narrow therapeutic index, such as theophylline, in clinical situations.

Detection of anti-isoniazid and anti-cytochrome P450 antibodies in patients with isoniazid-induced liver failure

Isoniazid (INH)-induced hepatotoxicity remains one of the most common causes of drug-induced idiosyncratic liver injury and liver failure. This form of liver injury is not believed to be immune-mediated because it is not usually associated with fever or rash, does not recur more rapidly on rechallenge, and previous studies have failed to identify anti-INH antibodies (Abs). In this study, we found Abs present in sera of 15 of 19 cases of INH-induced liver failure. Anti-INH Abs were present in 8 sera; 11 had anti-cytochrome P450 (CYP)2E1 Abs, 14 had Abs against CYP2E1 modified by INH, 14 had anti-CYP3A4 antibodies, and 10 had anti-CYP2C9 Abs. INH was found to form covalent adducts with CYP2E1, CYP3A4, and CYP2C9. None of these Abs were detected in sera from INH-treated controls without significant liver injury. The presence of a range of antidrug and autoAbs has been observed in other drug-induced liver injury that is presumed to be immune mediated.

CONCLUSION

These data provide strong evidence that INH induces an immune response that causes INH-induced liver injury.

Effect of anti-tuberculosis therapy on polymorphic drug metabolizing enzyme CYP2C9 using phenytoin as a probe drug

OBJECTIVES

Patients on anti-tuberculosis therapy (ATT) are more prone to drug interactions in the presence of coexisting illnesses which warrant drug therapy. Rifampicin is a strong CYP enzyme inducer while isoniazid is a potent CYP inhibitor. The objective of the study was to find the net effect of one month ATT on CYP2C9 enzyme and to correlate it with respect to the CYP2C9 genetic polymorphisms.

MATERIALS AND METHODS

Forty eight newly diagnosed tuberculosis patients were included in the study based on the inclusion-exclusion criteria. Before commencing ATT, they were given a single dose of phenytoin 300 mg as a probe drug for CYP2C9. Blood sample was collected after three hours to carry out CYP2C9 genotyping by PCR-RFLP method. Phenotyping for CYP2C9 enzyme was done by measuring the ratio of phenytoin and its metabolite p-HPPH (para hydroxy phenyl hydantoin) by reverse phase HPLC (high performance liquid chromatography) method before and after one month of ATT.

RESULTS

In the CYP2C9*1*1 genotype, the mean plasma concentrations of phenytoin before and after one month of ATT were 5.2 ± 0.3 μg/ml and 3.5 ± 0.4 μg/ml respectively, a reduction by 33% showing significant induction (P < 0.001). There was also significant decrease in the metabolic ratio after one month of ATT from 23.2 ± 4.8 to 10.1 ± 1.9 (P < 0.001). The metabolic ratio was also observed to reduce significantly (P < 0.05) when the CYP2C9*1*2, CYP2C9*1*3, and CYP2C9*3*3 data were pooled together.

CONCLUSION

The presence of polymorphisms in the CYP2C9 gene does not affect the induction potential of ATT.

[Mechanism of hepatoprotective action of methionine and composition "Metovitan" against a background of antituberculosis drug administration to rats]

Oral administration of antituberculosis drugs to rats for 60 days in doses that are equivalent to clinical ones, causes changes in mRNA levels expression of liver cytochrome P-450 isoforms CYP3A2, CYP2C23, CYP2E1 and pro- and antioxidant state. Experimental composition "Metovitan" given with anti-TB drugs provided a correction of these abnormalities, that is evidenced by modulation of the level of CYP3A2, CYP2C23, CYP2E1 gene expression and antioxidant activity, inhibition of lipid peroxidation. "Metovitan" normalizes the enzymatic activity and content of total billirubin in the blood serum, shows high hepatoprotective properties, exceeding the efficiency of methionine.

Phenotypic interaction of simultaneously administered isoniazid and phenytoin in patients with tuberculous meningitis or tuberculoma having seizures

Treatment of tuberculous meningitis or tuberculoma has become complicated because of adverse drug interactions found amongst antitubercular and anticonvulsant drugs. The aim of the study is to evaluate the effect of simultaneously administered isoniazid (300 mg/day) and phenytoin (300 mg/day) on 60 patients with tuberculous meningitis or tuberculoma having seizures. Plasma samples were analyzed for isoniazid, acetylated-isoniazid (AcINH) and phenytoin levels by high performance liquid chromatography at 3h of drugs administration and patients were classified as rapid or slow acetylator on the basis of metabolic ratio of isoniazid (Rm) and percentage of acetylated-isoniazid (%AcINH). Out of 60 patients studied, 23 were slow acetylators and 37 were rapid acetylators. Slow acetylators revealed higher plasma isoniazid levels and lower plasma AcINH levels, metabolic ratio and %AcINH as compared to rapid acetylators. Plasma phenytoin levels were found to be significantly higher (above therapeutic range) in slow acetylators as compared to rapid acetylators. Plasma phenytoin concentration was moderately strong, negatively correlated with metabolic ratio (r=-0.439, P<0.001) and %AcINH (r=-0.729, P<0.001). Eight comatose patients (34.8%) also showed significantly higher plasma phenytoin levels. Our results suggest that assessment of acetylator status and plasma phenytoin level is critical for dose optimization of isoniazid and phenytoin and to predict the patients at risk of intoxication.

Rifampicin-warfarin interaction leading to macroscopic hematuria: a case report and review of the literature

Background

Rifampicin remains one of the first-line drugs used in tuberculosis therapy. This drug´s potential to induce the hepatic cytochrome P450 oxidative enzyme system increases the risk of drug-drug interactions. Thus, although the presence of comorbidities typically necessitates the use of multiple drugs, the co-administration of rifampicin and warfarin may lead to adverse drug events. We report a bleeding episode after termination of the co-administration of rifampicin and warfarin and detail the challenges related to international normalized ratio (INR) monitoring.

Case presentation

A 59-year-old Brazilian woman chronically treated with warfarin for atrial fibrillation (therapeutic INR range: 2.0-3.0) was referred to a multidisciplinary anticoagulation clinic at a university hospital. She showed anticoagulation resistance at the beginning of rifampicin therapy, as demonstrated by repeated subtherapeutic INR values. Three months of sequential increases in the warfarin dosage were necessary to reach a therapeutic INR, and frequent visits to the anticoagulation clinic were needed to educate the patient about her pharmacotherapy and to perform the warfarin dosage adjustments. The warfarin dosage also had to be doubled at the beginning of rifampicin therapy. However, four weeks after rifampicin discontinuation, an excessively high INR was observed (7.22), with three-day macroscopic hematuria and the need for an immediate reduction in the warfarin dosage. A therapeutic and stable INR was eventually attained at 50% of the warfarin dosage used by the patient during tuberculosis therapy.

Conclusions

The present case exemplifies the influence of rifampicin therapy on warfarin dosage requirements and the increased risk of bleeding after rifampicin discontinuation. Additionally, this case highlights the need for warfarin weekly monitoring after stopping rifampicin until the maintenance dose of warfarin has decreased to the amount administered before rifampicin use. In particular, patients with cardiovascular diseases and active tuberculosis represent a group with a substantial risk of drug-drug interactions. Learning how to predict and monitor drug-drug interactions may help reduce the incidence of clinically significant adverse drug events.

Relationship between weight, efavirenz exposure, and virologic suppression in HIV-infected patients on rifampin-based tuberculosis treatment in the AIDS Clinical Trials Group A5221 STRIDE Study

BACKGROUND

Rifampin (RIF) upregulates CYP 450 isoenzymes, potentially lowering efavirenz (EFV) exposure. The US EFV package insert recommends an EFV dose increase for patients on RIF weighing ≥50 kg. We conducted a pharmacokinetic study to evaluate EFV trough concentrations (Cmin) and human immunodeficiency virus (HIV) virologic suppression in patients on EFV (600 mg) and RIF-based tuberculosis treatment in the multicenter randomized trial (ACTG A5221).

METHODS

EFV Cmin was measured 20-28 hours post-EFV dose at weeks 4, 8, 16, 24 on-RIF and weeks 4, 8 off-RIF. Results were evaluated with 2-sided Wilcoxon rank-sum, χ(2), Fisher exact tests and logistic regression (5% type I error rate).

RESULTS

Seven hundred eighty patients received EFV; 543 provided ≥1 EFV Cmin. Median weight was 52.8 kg (interquartile range [IQR], 48.0-59.5), body mass index 19.4 kg/m(2) (IQR, 17.5-21.6), and age 34 years (IQR, 29-41); 63% were male, 74% black. Median Cmin was 1.96 µg/mL on-RIF versus 1.80 off-RIF (P = .067). Cmin were significantly higher on-RIF versus off-RIF in blacks (2.08 vs 1.75, P = .005). Weight ≥60 kg on-RIF, compared to <60 kg, was associated with lower EFV Cmin (1.68 vs 2.02, P = .021). However, weight ≥60 kg was associated with more frequent HIV RNA < 400 copies/mL at week 48, compared to weight <60 kg (81.9% vs 73.8%, P = .023).

CONCLUSIONS

EFV and RIF-based tuberculosis therapy coadministration was associated with a trend toward higher, not lower, EFV Cmin compared to EFV alone. Patients weighing ≥60 kg had lower median EFV Cmin versus those <60 kg, but there was no association of higher weight with reduced virologic suppression. These data do not support weight-based dosing of EFV with RIF.

The safety, effectiveness and concentrations of adjusted lopinavir/ritonavir in HIV-infected adults on rifampicin-based antitubercular therapy

Objective

Rifampicin co-administration dramatically reduces plasma lopinavir concentrations. Studies in healthy volunteers and HIV-infected patients showed that doubling the dose of lopinavir/ritonavir (LPV/r) or adding additional ritonavir offsets this interaction. However, high rates of hepatotoxicity were observed in healthy volunteers. We evaluated the safety, effectiveness and pre-dose concentrations of adjusted doses of LPV/r in HIV infected adults treated with rifampicin-based tuberculosis treatment.

Methods

Adult patients on a LPV/r-based antiretroviral regimen and rifampicin-based tuberculosis therapy were enrolled. Doubled doses of LPV/r or an additional 300 mg of ritonavir were used to overcome the inducing effect of rifampicin. Steady-state lopinavir pre-dose concentrations were evaluated every second month.

Results

18 patients were enrolled with a total of 79 patient months of observation. 11/18 patients were followed up until tuberculosis treatment completion. During tuberculosis treatment, the median (IQR) pre-dose lopinavir concentration was 6.8 (1.1–9.2) mg/L and 36/47 (77%) were above the recommended trough concentration of 1 mg/L. Treatment was generally well tolerated with no grade 3 or 4 toxicity: 8 patients developed grade 1 or 2 transaminase elevation, 1 patient defaulted additional ritonavir due to nausea and 1 patient developed diarrhea requiring dose reduction. Viral loads after tuberculosis treatment were available for 11 patients and 10 were undetectable.

Conclusion

Once established on treatment, adjusted doses of LPV/r co-administered with rifampicin-based tuberculosis treatment were tolerated and LPV pre-dose concentrations were adequate.

Clinical pharmacology and lesion penetrating properties of second- and third-line antituberculous agents used in the management of multidrug-resistant (MDR) and extensively-drug resistant (XDR) tuberculosis

Failure of first-line chemotherapy to cure tuberculosis (TB) patients occurs, in part, because of the development of resistance to isoniazid (INH) and rifampicin (RIF) the two most sterilizing agents in the four-drug regimen used to treat primary infections. Strains resistant to both INH and RIF are termed multidrug-resistant (MDR). Treatment options for MDR patients involve a complex array of twenty different drugs only two classes of which are considered to be highly effective (fluoroquinolones and aminoglycosides). Resistance to these two classes results in strains known as extensively drug-resistant (XDR) and these types of infections are becoming increasingly common. Many of the remaining agents have poorly defined pharmacology but nonetheless are widely used in the treatment of this disease. Several of these agents are known to have highly variable exposures in healthy volunteers and little is known in the patients in which they must be used. Therapeutic drug monitoring (TDM) is infrequently used in the management of MDR or XDR disease yet the clinical pharmacokinetic studies that have been done suggest this might have a large impact on disease outcome. We review what is known about the pharmacologic properties of each of the major classes of second- and third-line antituberculosis agents and suggest where judicious use of TDM would have the maximum possible impact. We summarize the state of knowledge of drug-drug interactions (DDI) in these classes of agents and those that are currently in clinical trials. Finally we consider what little is known about the ability of TB drugs to reach their ultimate site of action--the interior of a granuloma by penetrating the diseased lung area. Careful consideration of the pharmacology of these agents is essential if we are to avoid further fueling the growing epidemic of highly drug-resistant TB and critical in the development of new antituberculosis drugs.

Genetic variations of NAT2 and CYP2E1 and isoniazid hepatotoxicity in a diverse population

AIMS

TB is a serious global public health problem. Isoniazid, a key drug used to treat latent TB, can cause hepatotoxicity in some patients. This pilot study investigated the effects of genetic variation in NAT2 and CYP2E1 on isoniazid-induced hepatotoxicity in TB contacts in British Columbia, Canada.

MATERIALS & METHODS

DNA re-sequencing was used to establish the spectrum of genetic variation in the exons, promoter and conserved regions of NAT2 in all subjects. For CYP2E1, the CYP2E1*1C polymorphism was genotyped by PCR-RFLP. Association tests of NAT2 variants and haplotypes, as well acetylator types were performed.

RESULTS

We enrolled 170 subjects on isoniazid treatment (23 cases and 147 controls). Systematic re-sequencing of NAT2 revealed 18 known and 10 novel variants.

CONCLUSION

No single genetic variant of NAT2 and CYP2E1 showed a significant association with isoniazid-induced hepatotoxicity in this highly heterogeneous population. There was evidence of a trend for increasing hepatotoxicity risk across the rapid, intermediate and slow acetylator groups (p = 0.08).

CYP2B6 (c.516G-->T) and CYP2A6 (*9B and/or *17) polymorphisms are independent predictors of efavirenz plasma concentrations in HIV-infected patients

AIMS

Interindividual variability in efavirenz pharmacokinetics is not entirely explained by the well-recognized CYP2B6 516G-->T single nucleotide polymorphism. The aim of this study was to determine whether polymorphisms in the CYP2A6 gene can be used to enhance the predictability of efavirenz concentrations in human immunodeficiency virus (HIV)-infected native African patients.

METHODS

Mid-dose efavirenz plasma concentrations were determined at 4 and 8 weeks following initiation of antiretroviral therapy in 65 HIV-infected Ghanaian patients. Selected CYP2B6 and CYP2A6 genotypes were determined by commercial 5'-nuclease assays. Relationships between averaged 4- and 8-week mid-dose efavirenz concentrations, demographic variables and genotypes were evaluated by univariate and multivariate statistical approaches including gene-gene interactions.

RESULTS

CYP2B6 c.516G-->T, CYP2B6 c.983T-->C, CYP2A6*9B and CYP2A6*17 allele frequencies were 45, 4, 5 and 12%, respectively. Rifampicin therapy, gender, age and body mass index had no significant influence on efavirenz mid-dose concentrations. Median efavirenz concentrations were more than five times higher (P < 0.001) in patients with CYP2B6 c.516TT genotype compared with GG and GT genotypes. Although none of the CYP2A6 genotypes was associated with altered efavirenz concentrations individually, CYP2A6*9B and/or CYP2A6*17 carriers showed a 1.8 times higher median efavirenz concentration (P= 0.017) compared with noncarriers. Multiple linear regression analysis indicated that the CYP2B6 c.516G-->T polymorphism and CYP2A6 slow-metabolizing variants accounted for as much as 36 and 12% of the total variance in efavirenz concentrations, respectively.

CONCLUSIONS

Our findings support previous work showing efavirenz oxidation by CYP2A6, and suggest that both CYP2A6 and CYP2B6 genotyping may be useful for predicting efavirenz plasma concentrations.

Treatment of tuberculosis in children

The treatment of children with TB is influenced by a number of factors specific to both the bacterium and the child. We review the variables impacting the selection of individual medications; indications, pharmacology, dosing and side effects for first- and second-line agents; adjunctive therapy; and special cases, including treatment of TB in HIV-infected children and multidrug-resistant TB. Finally, evolving trends in TB therapy, such as the impact of HIV and multidrug-resistant TB on future therapeutics, emerging or re-emerging medication options, shorter-course regimens and immunomodulation, are discussed.

Antituberculosis drug-induced hepatotoxicity: concise up-to-date review

The cornerstone of tuberculosis management is a 6-month course of isoniazid, rifampicin, pyrazinamide and ethambutol. Compliance is crucial for curing tuberculosis. Adverse effects often negatively affect the compliance, because they frequently require a change of treatment, which may have negative consequences for treatment outcome. In this paper we review the incidence, pathology and clinical features of antituberculosis drug-induced hepatotoxicity, discuss the metabolism and mechanisms of toxicity of isoniazid, rifampicin and pyrazinamide, and describe risk factors and management of antituberculosis drug-induced hepatotoxicity. The reported incidence of antituberculosis drug-induced hepatotoxicity, the most serious and potentially fatal adverse reaction, varies between 2% and 28%. Risk factors are advanced age, female sex, slow acetylator status, malnutrition, HIV and pre-existent liver disease. Still, it is difficult to predict what patient will develop hepatotoxicity during tuberculosis treatment. The exact mechanism of antituberculosis drug-induced hepatotoxicity is unknown, but toxic metabolites are suggested to play a crucial role in the development, at least in the case of isoniazid. Priorities for future studies include basic studies to elucidate the mechanism of antituberculosis drug-induced hepatotoxicity, genetic risk factor studies and the development of shorter and safer tuberculosis drug regimens.

Computational models to assign biopharmaceutics drug disposition classification from molecular structure

PURPOSE

We applied in silico methods to automatically classify drugs according to the Biopharmaceutics Drug Disposition Classification System (BDDCS).

MATERIALS AND METHODS

Models were developed using machine learning methods including recursive partitioning (RP), random forest (RF) and support vector machine (SVM) algorithms with ChemDraw, clogP, polar surface area, VolSurf and MolConnZ descriptors. The dataset consisted of 165 training and 56 test set molecules.

RESULTS

RF model 3, RP model 1, and SVM model 1 can correctly predict 73.1, 63.6 and 78.6% test compounds in classes 1, 2 and 3, respectively. Both RP and SVM models can be used for class 4 prediction. The inclusion of consensus analysis resulted in improved test set predictions for class 2 and 4 drugs.

CONCLUSIONS

The models can be used to predict BDDCS class for new compounds from molecular structure using readily available molecular descriptors and software, representing an area where in silico approaches could aid the pharmaceutical industry in speeding drugs to the patient and reducing costs. This could have significant applications in drug discovery to identify molecules that may have future developability issues.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.

The effect of rifampicin and pyrazinamide on isoniazid pharmacokinetics in rats

Tuberculosis chemotherapy involves combination of the drugs isoniazid (INH), rifampicin (RMP) and pyrazinamide (PYR) for a 6-month period. The present work investigated the influence of RMP and PYR on the pharmacokinetic parameters of INH when groups of rats were pre-treated for 21 days with INH alone or in combination with RMP and/or PYR, in the following amounts per kg body weight: INH 100 mg; INH 100 mg+RMP 100 mg; INH 100 mg+PYR 350 mg; INH 100 mg+PYR 350 mg+RMP 100 mg. It was found that the co-administration of PYR caused an increase in the INH distribution volume (V(d)/F), half-life of elimination (t(1/2beta)) and clearance (Cl(T)/F), and a decrease in the area under curve 0 to 24 h (AUC). Co-administration of RMP caused an increase in the Cl(T)/F and a decrease in the AUC. The combination INH+PYR+RMP caused an increase in the Cl(T)/F and a decrease in the AUC. These significant pharmacokinetic interactions between the tuberculostatic drugs might be related to differences in the therapeutic and toxic effects.

Effects of Continuous Ingestion of Herbal Teas on Intestinal CYP3A in the Rat

Tenryocha, rooibos, and guava teas are widely consumed as herbal beverages, especially as a therapy against pollen allergy. To investigate the possible herbal tea-drug interaction the effect of continuous ingestion of these teas on cytochrome P450 (CYP) 3A were studied. Rats (n = 6) were allowed free access to either tea (experimental groups) or water (control) for two weeks. Midazolam (MDZ) (20 mg/kg) was orally administered and the serum concentration was determined. The area under the serum concentration-time curve (AUC(0-infinity)) and the maximum serum concentrations (C(max)) of MDZ were reduced by more than 60% after the treatment of tenryocha and rooibos tea (P<0.05). Intestinal MDZ 1'- and 4-hydroxylation activities mediated by CYP3A were increased in tenryocha and rooibos tea-treated group by 50% compared to the control group, although the results were not statistically significant. Furthermore, the Western blot analysis showed that CYP3A content was significantly increased in the intestine after the treatment of these teas (P<0.05). Hepatic MDZ hydroxylation and CYP3A content were slightly increased by these teas. The results suggested that two weeks ingestion of tenryocha and rooibos tea reduced serum concentration of MDZ by the induction of intestinal CYP3A. The possible interaction between tenryocha or rooibos tea and medicines mediated by CYP3A was suggested.