Sequence variations in the UDP-glucuronosyltransferase 2B7 (UGT2B7) gene: identification of 10 novel single nucleotide polymorphisms (SNPs) and analysis of their relevance to morphine glucuronidation in cancer patients

Impact of CYP2D6, MAOA, and UGT2B7 genetic variants on recurrence of Plasmodium Vivax in the Brazilian Amazon

The biotransformation of primaquine is mediated by cytochrome P-450 (CYP) enzymes and monoamine oxygenase A (MAO-A). Polymorphisms in the genes that encode these enzymes can alter the clinical response of patients with Plasmodium vivax malaria, leading to therapeutic failure and recurrences. This study aimed to investigate the influence of variations in CYP2D6, MAOA, and UGT2B7 genes on recurrences of vivax malaria. In this case-control study, 72 individuals with vivax malaria were divided into two groups: 18 recurrences and 54 non-recurrences cases. Genotyping of CYP2D6, MAOA, and UGT2B7 was performed using a TaqMan assay and Real-time PCR. The frequency of CYP2D6 alleles was similar between the groups, except for the reduced-function allele *4, which was more frequent in the recurrence group (p = 0.019). Furthermore, the CYP2D6 normal metabolizers (gNM) phenotype had a higher frequency in individuals without recurrence (p = 0.039). An association was found between mutated MAOA genotypes (CC + CT) and a shorter time to recurrence compared to the wild-type (p = 0.0437). However, no association was found between UGT2B7 genotypes and recurrence. These findings suggest that genetic variations in both CYP2D6 and MAOA may contribute to the therapeutic failure of primaquine, reinforcing the importance of pharmacogenetics in monitoring antimalarial therapies.

Impact of Pharmacogenomics in Clinical Practice

Polymorphisms of genes encoding drug metabolizing enzymes and transporters can significantly modify pharmacokinetics, and this can be associated with significant differences in drug efficacy, safety, and tolerability. Moreover, genetic variants of some components of the immune system can explain clinically relevant drug-related adverse events. However, the implementation of drug dose individualization based on pharmacogenomics remains scarce. In this narrative review, the impact of genetic variations on the disposition, safety, and tolerability of the most commonly prescribed drugs is reported. Moreover, reasons for poor implementation of pharmacogenomics in everyday clinical settings are discussed. The literature analysis showed that knowledge of how genetic variations can modify the effectiveness, safety, and tolerability of a drug can lead to the adjustment of usually recommended drug dosages, improve effectiveness, and reduce drug-related adverse events. Despite some efforts to introduce pharmacogenomics in clinical practice, presently very few centers routinely use genetic tests as a guide for drug prescription. The education of health care professionals seems critical to keep pace with the rapidly evolving field of pharmacogenomics. Moreover, multimodal algorithms that incorporate both clinical and genetic factors in drug prescribing could significantly help in this regard. Obviously, further studies which definitively establish which genetic variations play a role in conditioning drug effectiveness and safety are needed. Many problems must be solved, but the advantages for human health fully justify all the efforts.

Effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on sublingual buprenorphine metabolism in heroin addicts: An improved PCR-RFLP assay for the detection of rs7662029 polymorphism

This study aimed to determine the effects of UGT2B7 rs7662029 and rs7439366 polymorphisms on plasma buprenorphine (BUP) concentration and different treatment responses in a sample of 109 patients with opioid use disorder (OUD) treated with sublingual BUP/naloxone. Polymorphisms were analysed by PCR-RFLP. Plasma concentrations of BUP and its metabolite norbuprenorphine were detected by LC-MS/MS. Craving, withdrawal, depression and anxiety were measured by appropriate scales. OUD patients with rs7439366 CC or rs7662029 GG genotypes had significantly lower dose-normalized (BUP/D) and dose/kg-normalized BUP (BUP/D.kg-1) levels than those who were CT or AA carriers. Significant associations between UGT2B7 rs7662029 and increased craving (p = 0.037) and withdrawal symptoms (p = 0.029) were detected. Our findings were pointing to an important role of UGT2B7 in the metabolism of sublingual BUP/naloxone in the heroin addicts for the first time. A novel PCR-RFLP assay was developed for the determination of UGT2B7 rs7662029 polymorphism, based on utilizing novel restriction enzyme.

Progress, Challenges, and Prospects of Research on the Effect of Gene Polymorphisms on Adverse Reactions to Opioids

The abuse of opioids has become one of the most serious concerns in the world. Opioid use can cause serious adverse reactions, including respiratory depression, postoperative nausea and vomiting, itching, and even death. These adverse reactions are also important complications of clinical application of opioid drugs that may affect patient safety and recovery. Due to the fear of adverse reactions of opioids, clinicians often do not dare to use opioids in an adequate or appropriate amount, thus affecting the clinical medication strategy and the quality of treatment for patients. The prediction of adverse reactions to opioids is one of the most concerned problems in clinical practice. At present, the correlation between gene polymorphism and the efficacy of opiates has been widely studied and preliminarily confirmed, but the research on the effect of gene polymorphism on the adverse reactions of opiates is relatively limited. Existing studies have made encouraging progress in predicting the incidence and severity of adverse opioid reactions and clinical management by using genetic testing, but most of these studies are single-center, small-sample clinical studies or animal experiments, which have strong limitations. When the same receptor or enzyme is studied by different experimental methods, different or even opposite conclusions can be drawn. These phenomena indicate that the correlation between gene polymorphism and adverse opioid reaction still needs further research and demonstration. At present, it is still too early to use genetic testing to predict opioid adverse reactions in clinic. In this paper, the correlation between gene polymorphism and adverse opioid reactions and a small number of clinical applications were reviewed in terms of pharmacokinetics and pharmacodynamics, in order to provide some suggestions for future research and clinical drug decision making.

Effects of genetic polymorphism of drug-metabolizing enzymes on the plasma concentrations of antiepileptic drugs in Chinese population

As a chronic brain disease, epilepsy affects ~50 million people worldwide. The traditional antiepileptic drugs (AEDs) are widely applied but showing various problems. Although the new AEDs have partially solved the problems of traditional AEDs, the current clinical application of traditional AEDs are not completely replaced by new drugs, particularly due to the large individual differences in drug plasma concentrations and narrow therapeutic windows among patients. Therefore, it is still clinically important to continue to treat patients using traditional AEDs with individualized therapeutic plans. To date, our understanding of the molecular and genetic mechanisms regulating plasma concentrations of AEDs has advanced rapidly, expanding the knowledge on the effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of AEDs. It is increasingly imperative to summarize and conceptualize the clinical significance of recent studies on individualized therapeutic regimens. In this review, we extensively summarize the critical effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of several commonly used AEDs as well as the clinical significance of testing genotypes related to drug metabolism on individualized drug dosage. Our review provides solid experimental evidence and clinical guidance for the therapeutic applications of these AEDs.

Drug-drug-gene interactions as mediators of adverse drug reactions to diclofenac and statins: a case report and literature review

Concomitant treatment with drugs that inhibit drug metabolising enzymes and/or transporters, such as commonly prescribed statins and nonsteroidal anti-inflammatory drugs (NSAIDs), has been associated with prolonged drug exposure and increased risk of adverse drug reactions (ADRs) due to drug-drug interactions. The risk is further increased in patients with chronic diseases/comorbidities who are more susceptible because of their genetic setup or external factors. In that light, we present a case of a 46-year-old woman who had been experiencing acute renal and hepatic injury and myalgia over two years of concomitant treatment with diclofenac, atorvastatin, simvastatin/fenofibrate, and several other drugs, including pantoprazole and furosemide. Our pharmacogenomic findings supported the suspicion that ADRs, most notably the multi-organ toxicity experienced by our patient, may be owed to drug-drug-gene interactions and increased bioavailability of the prescribed drugs due to slower detoxification capacity and decreased hepatic and renal elimination. We also discuss the importance of CYP polymorphisms in the biotransformation of endogenous substrates such as arachidonic acid and their modulating role in pathophysiological processes. Yet even though the risks of ADRs related to the above mentioned drugs are substantially evidenced in literature, pre-emptive pharmacogenetic analysis has not yet found its way into common clinical practice.

Genetic Polymorphisms Affecting Cardiac Biomarker Concentrations in Children with Cancer: an Analysis from the "European Paediatric Oncology Off-patents Medicines Consortium" (EPOC) Trial

BACKGROUND AND OBJECTIVES

Doxorubicin plays an essential role in the treatment of paediatric cancers. Defining genotypes with a higher risk for developing anthracycline-induced cardiotoxicity could help to reduce cardiotoxicity.

METHODS

Data originated from a phase II study assessing the pharmacokinetics of doxorubicin in 100 children. Studied patients (0-17 years) were treated for solid tumours or leukaemia. Two cycles of doxorubicin were studied. Concentrations of natriuretic peptides proANP, BNP and NT-proBNP and cardiac troponins T and I were measured at five time points before, during and after two cycles of doxorubicin treatment. Genotypes of 17 genetic polymorphisms in genes encoding for anthracycline metabolizing enzymes and drug transporters were determined for each patient. We analysed the influence of genotypes on cardiac biomarker concentrations at different time points by a Kruskal-Wallis test. To perform a pairwise comparison significant genetic polymorphisms with more than two genotypes were analysed by a post hoc test.

RESULTS

The Kruskal-Wallis tests and the post hoc-tests showed a significant association for seven genetic polymorphisms (ABCB1-rs1128503, ABCB1-rs1045642, ABCC1-rs4148350, CBR3-rs8133052, NQO2-in/del, SLC22A16-rs714368 and SLC22A16-rs6907567) with the concentration of at least one biomarker at one or more time points. We could not identify any polymorphism with a consistent effect on any biomarker over the whole treatment period.

CONCLUSIONS

In this study of patients treated with doxorubicin for different tumour entities, seven genetic polymorphisms possibly influencing the pharmacokinetics and pharmacodynamics of doxorubicin could lead occasionally to differences in the concentration of cardiac biomarkers. Since, the role of cardiac biomarkers for monitoring anthracycline-induced cardiotoxicity has not yet been clarified, further trials with a long follow-up time are required to assess the impact of these genetic polymorphisms on chemotherapy-related cardiotoxicity.

TRIAL REGISTRATION

EudraCT number: 2009-011454-17.

Uridine Glucuronosyltransferase 2B7 Polymorphism-Based Pharmacogenetic Dosing of Epirubicin in FEC Chemotherapy for Early-Stage Breast Cancer

BACKGROUND

Epirubicin is metabolized by uridine glucuronosyltransferase 2B7 (UGT2B7). Patients homozygous for the minor allele (CC) in the UGT2B7 -161 promoter polymorphism have lower clearance and significantly higher rates of leukopenia compared to wild-type homozygote (TT) or heterozygote (CT) patients. This study was designed to determine if TT and CT genotype patients could tolerate a higher epirubicin dose compared to CC genotype patients.

PATIENTS AND METHODS

We studied women with histologically confirmed non-metastatic, invasive breast cancer who were scheduled to receive at least three cycles of FE₁₀₀C in the (neo)adjuvant setting. Patients received standard-dose FE₁₀₀C during the first 21-day cycle. Based on genotype, the epirubicin dose was escalated in the second and third cycles to 115 and 130 mg/m² or to 120 and 140 mg/m² for CT and TT genotype patients, respectively. The main outcome measurements were myelosuppression and dose-limiting toxicity. These were analyzed for relationships with the three genotypes.

RESULTS

Forty-five patients were enrolled (10 CC, 21 CT, and 14 TT genotypes) and received 100 mg/m² of epirubicin in the first cycle. Twelve and 10 TT patients were dose escalated at the second and third cycles, respectively; 16 CT patients were dose escalated at the second and third cycles. Leukopenia, but not febrile neutropenia, was genotype and dose dependent and increased in patients with CT and TT genotypes as their dose was increased. However, the third-cycle leukopenia rates were comparable to patients with the CC genotype receiving standard-dose epirubicin.

CONCLUSION

Pharmacogenetically guided epirubicin dosing is well tolerated and allowed dose escalation without increased toxicity.

Relative addictive potential of opioid analgesic agents

Opioid overdoses and deaths continue to be a problem in the USA with a significant portion related to prescribed opioid analgesic agents. The role of pharmacogentic factors in opioid addiction is an active area of research. While all opioid analgesic agents have some addictive potential, it is clear that there are some with greater addictive potential. Oxycodone is the most widely abused opioid analgesic and it appears to predispose to chronic use with high likability by users. Fentanyl and hydromorphone are both very lipophilic allowing rapid penetration into the CNS, but are not rated as highly as other agents. Providers should consider the risk of addiction with the opioids they prescribe and give those with a lower addictive potential.

Genetics and Opioids: Towards More Appropriate Prescription in Cancer Pain

Opioids are extensively used in patients with cancer pain; despite their efficacy, several patients can experience ineffective analgesia and/or side effects. Pharmacogenetics is a new approach to drug prescription based on the “personalized-medicine” concept, i.e., the ability of tailoring treatments to each individual’s genetic/genomic profile. Pharmacogenetics aims to identify specific genetic variants that influence pharmacokinetics and pharmacodynamics of drugs, better determining their effectiveness/safety profile. Opioid response is a complex scenario, but some gene variants have shown a correlation with pain sensitivity, as well as with opioid metabolism and clinical efficacy/adverse events. Although questions remain unanswered, some of these gene variants may already be used to identify specific patients’ phenotypes that are more prone to experience better clinical response (i.e., better analgesia and/or less adverse events). Once adopted, this approach to opioid prescription may improve a patient’s outcome. This review summarizes the available data on genetic variants and opioid response: we will focus on basic pharmacogenetic and its impact in the clinical scenario discussing how they may lead to more appropriate opioid prescription in cancer patients.

Morphine Dose Optimization in Critically Ill Pediatric Patients With Acute Respiratory Failure: A Population Pharmacokinetic-Pharmacogenomic Study

OBJECTIVE

To develop a pharmacokinetic-pharmacogenomic population model of morphine in critically ill children with acute respiratory failure.

DESIGN

Prospective pharmacokinetic-pharmacogenomic observational study.

SETTING

Thirteen PICUs across the United States.

PATIENTS

Pediatric subjects (n = 66) mechanically ventilated for acute respiratory failure, weight greater than or equal to 7 kg, receiving morphine and/or midazolam continuous infusions.

INTERVENTIONS

Serial blood sampling for drug quantification and a single blood collection for genomic evaluation.

MEASUREMENTS AND MAIN RESULTS

Concentrations of morphine, the two main metabolites, morphine-3-glucuronide and morphine-6-glucuronide, were quantified by high-performance liquid chromatography tandem mass spectrometry/mass spectroscopy. Subjects were genotyped using the Illumina HumanOmniExpress genome-wide single nucleotide polymorphism chip. Nonlinear mixed-effects modeling was performed to develop the pharmacokinetic-pharmacogenomic model. A two-compartment model with linear elimination and two individual compartments for metabolites best describe morphine disposition in this population. Our analysis demonstrates that body weight and postmenstrual age are relevant predictors of pharmacokinetic parameters of morphine and its metabolites. Furthermore, our research shows that a duration of mechanical ventilation greater than or equal to 10 days reduces metabolite formation and elimination upwards of 30%. However, due to the small sample size and relative heterogeneity of the population, no heritable factors associated with uridine diphosphate glucuronyl transferase 2B7 metabolism of morphine were identified.

CONCLUSIONS

The results provide a better understanding of the disposition of morphine and its metabolites in critically ill children with acute respiratory failure requiring mechanical ventilation due to nonheritable factors. It also provides the groundwork for developing additional studies to investigate the role of heritable factors.

Midazolam Dose Optimization in Critically Ill Pediatric Patients With Acute Respiratory Failure: A Population Pharmacokinetic-Pharmacogenomic Study

OBJECTIVES

To develop a pharmacokinetic-pharmacogenomic population model of midazolam in critically ill children with primary respiratory failure.

DESIGN

Prospective pharmacokinetic-pharmacogenomic observational study.

SETTING

Thirteen PICUs across the United States.

PATIENTS

Pediatric subjects mechanically ventilated for acute respiratory failure, weight greater than or equal to 7 kg, receiving morphine and/or midazolam continuous infusions.

INTERVENTIONS

Serial blood sampling for drug quantification and a single blood collection for genomic evaluation.

MEASUREMENTS AND MAIN RESULTS

Concentrations of midazolam, the 1' (1`-hydroxymidazolam metabolite) and 4' (4`-hydroxymidazolam metabolite) hydroxyl, and the 1' and 4' glucuronide metabolites were measured. Subjects were genotyped using the Illumina HumanOmniExpress genome-wide single nucleotide polymorphism chip. Nonlinear mixed effects modeling was performed to develop the pharmacokinetic-pharmacogenomic model. Body weight, age, hepatic and renal functions, and the UGT2B7 rs62298861 polymorphism are relevant predictors of midazolam pharmacokinetic variables. The estimated midazolam clearance was 0.61 L/min/70kg. Time to reach 50% complete mature midazolam and 1`-hydroxymidazolam metabolite/4`-hydroxymidazolam metabolite clearances was 1.0 and 0.97 years postmenstrual age. The final model suggested a decrease in midazolam clearance with increase in alanine transaminase and a lower clearance of the glucuronide metabolites with a renal dysfunction. In the pharmacogenomic analysis, rs62298861 and rs28365062 in the UGT2B7 gene were in high linkage disequilibrium. Minor alleles were associated with a higher 1`-hydroxymidazolam metabolite clearance in Caucasians. In the pharmacokinetic-pharmacogenomic model, clearance was expected to increase by 10% in heterozygous and 20% in homozygous for the minor allele with respect to homozygous for the major allele.

CONCLUSIONS

This work leveraged available knowledge on nonheritable and heritable factors affecting midazolam pharmacokinetic in pediatric subjects with primary respiratory failure requiring mechanical ventilation, providing the basis for a future implementation of an individual-based approach to sedation.

Adjustment of the area under the concentration curve by terminal rate constant for bioequivalence assessment in a parallel-group study of lamotrigine

AIM

A new strength of lamotrigine extended-release formulation unexpectedly failed to show bioequivalence with the existing strengths at the same dose in a parallel-group study. We report the post-hoc analyses conducted to identify the cause and propose an approach for future evaluations in similar situations.

METHODS

A seemingly bimodal distribution of the half-life among the study participants prompted the use of terminal-phase-rate-constant-adjusted area under the concentration curve as the endpoint for bioequivalence assessment. Population pharmacokinetic modelling was also performed to assess the bimodal distribution of apparent clearance and the potential treatment effects on bioavailability.

RESULTS

The cause for failing to achieve bioequivalence appeared to be a biased representation of a bimodal clearance distribution between the groups. The pharmacokinetic modelling with a mixture routine identified two subpopulations: 88% had a mean clearance of 1.99 l h-1 ; 12% had a mean clearance of 0.64 l h-1 . The low-clearance population was unequally represented by 13% and 4% of subjects in the reference and test groups, respectively, and treatment appeared to have no significant effect on oral bioavailability. The bioequivalence comparison using the adjusted area concluded with a 90% confidence interval of 0.91-1.06, suggesting that treatment had no significant effect on bioavailability and the formulations would meet regulatory criteria for bioequivalence.

CONCLUSIONS

The adjustment of the area under the concentration curve adjusted by terminal-phase rate constant should be considered for situational application in bioequivalence assessment when there are multiple clearance subpopulations in a parallel-group study.

Pharmacogenomics and Patient Treatment Parameters to Opioid Treatment in Chronic Pain: A Focus on Morphine, Oxycodone, Tramadol, and Fentanyl

Objective

Opioids are one of the most commonly prescribed medicines for chronic pain. However, their use for chronic pain has been controversial. The objective of this literature review was to identify the role of genetic polymorphisms on patient treatment parameters (opioid dose requirements, response, and adverse effects) for opioids used in malignant and nonmalignant chronic pain. The opioids that this review focuses on are codeine, morphine, oxycodone, tramadol, and fentanyl.

Method

A literature search of databases Medline and Embase was carried out, and studies up to April 2016 were included in this review. Studies were included based on a combination of key words: chronic pain and related terms, pharmacogenetics and related terms, and opioids and related terms.

Results

Among the 1,408 individual papers retrieved from the search in Medline and Embase, 32 original articles were included in this review, with none related to codeine. The 32 papers reported various study designs, opioids, and polymorphisms being studied for associations with treatment outcomes. This literature review reveals that variants in ABCB1, OPRM1, and COMT have been replicated for opioid dosing and variants in ABCB1 have been replicated for both treatment response and adverse effects.

Conclusions

Currently, there are few validated studies to form a strong evidence base to support pharmacogenomics testing when initiating opioid therapy. However, the field of pharmacogenomics in chronic pain is likely to expand over the coming years, with the increasing number of treatment options available and larger cohorts being assembled in order to identify true associations.

Effects of UGT2B7 Genetic Polymorphisms on Serum Concentrations of Valproic Acid in Chinese Children With Epilepsy Comedicated With Lamotrigine

BACKGROUND

Valproic acid (VPA) is widely used in the treatment of children with epilepsy. Genetic polymorphisms in genes encoding drug-metabolizing enzymes may be an important source of interindividual variability in VPA metabolism. VPA is a substrate of uridine diphosphate glucuronosyltransferase 2B7 (UGT2B7). In this study, we seek to evaluate the effects of genetic polymorphisms of the UGT2B7 gene on serum VPA concentrations in epileptic children comedicated with lamotrigine (LTG).

METHODS

We recruited 166 Chinese children with epilepsy who were treated with VPA in combination with LTG. Serum VPA and LTG concentrations were measured by fluorescence polarization immunoassay and high performance liquid chromatography, respectively. The UGT2B7 -161C > T in the 5'-upstream regions and 211 G > T, 372A > G, 735A > G, and 802C > T in the coding regions were genotyped using polymerase chain reaction amplification followed by direct automated DNA sequencing.

RESULTS

Our data show that patients carrying the variant UGT2B7 -161C > T or 802C > T genotypes had significantly higher adjusted VPA concentrations than those carrying the wild-type genotypes. The significant associations were potentiated after adjusted by age and adjusted LTG concentration. However, no associations were detected between the other studied UGT2B7 genotypes and adjusted VPA concentrations, even after adjusting by age and comedication.

CONCLUSIONS

These results suggest that the UGT2B7 -161C > T or 802C > T mutations affect VPA pharmacokinetics, which are potentially enhanced by age and concomitant LTG administration. These findings provide a potential mechanism underlying interindividual variation in the disposition of VPA in combination with LTG.

Effect of UDP-Glucuronosyltransferase (UGT) 1A Polymorphism (rs8330 and rs10929303) on Glucuronidation Status of Acetaminophen

Interindividual variability in polymorphic uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1) ascribed to genetic diversity is associated with relative glucuronidation level among individuals. The present research was aimed to study the effect of 2 important single nucleotide polymorphisms (SNPs; rs8330 and rs10929303) of UGT1A1 gene on glucuronidation status of acetaminophen in healthy volunteers (n = 109). Among enrolled volunteers, 54.13% were male (n = 59) and 45.87% were female (n = 50). The in vivo activity of UGT1A1 was investigated by high-performance liquid chromatography-based analysis of glucuronidation status (ie, acetaminophen and acetaminophen glucuronide) in human volunteers after oral intake of a single dose (1000 mg) of acetaminophen. The TaqMan SNP genotyping assay was used for UGT1A1 genotyping. The wild-type genotype (C/C) was observed the most frequent one for both SNPs (rs8330 and rs10929303) and associated with fast glucuronidator phenotypes. The distribution of variant genotype (G/G) for SNP rs8330 was observed in 5% of male and 8% of the female population; however, for SNP rs10929303, the G/G genotype was found in 8% of both genders. A trimodal distribution (fast, intermediate, and slow) based on phenotypes was observed. Among the male participants, the glucuronidation phenotypes were observed as 7% slow, 37% intermediate, and 56% fast glucuronidators; however, these findings for the females were slightly different as 8%, 32%, and 60% respectively. The k-statistics revealed a compelling evidence for good concordance between phenotype and genotype with a k value of 1.00 for SNP rs8330 and 0.966 for SNP rs10929303 in our population.

Pharmacogenetics of UGT1A4, UGT2B7 and UGT2B15 and Their Influence on Tamoxifen Disposition in Asian Breast Cancer Patients

Tamoxifen (TAM) is an established endocrine treatment for all stages of oestrogen receptor (ER)-positive breast cancer. Its complex metabolism leads to the formation of multiple active and inactive metabolites. One of the main detoxification and elimination pathways of tamoxifen and its active metabolites, 4-hydroxytamoxifen (4-OHT) and endoxifen, is via glucuronidation catalysed by uridine 5'-diphospho-glucuronosyltransferases (UGTs). However, few studies have comprehensively examined the impact of variations in the genes encoding the major hepatic UGTs on the disposition of tamoxifen and its metabolites. In the present study, we systematically sequenced exons, exon/intron boundaries, and flanking regions of UGT1A4, UGT2B7 and UGT2B15 in 240 healthy subjects of different Asian ethnicities (Chinese, Malays and Indians) to identify haplotype tagging single nucleotide polymorphisms. Subsequently, 202 Asian breast cancer patients receiving tamoxifen were genotyped for 50 selected variants in the three UGT genes to comprehensively investigate their associations with steady-state plasma levels of tamoxifen, its active metabolites and their conjugated counterparts. The UGT1A4 haplotype (containing variant 142T>G, L48 V defining the *3 allele) was strongly associated with higher plasma levels of TAM-N-glucuronide, with a twofold higher metabolic ratio of TAM-N-glucuronide/TAM observed in carriers of this haplotype upon covariate adjustment (P < 0.0001). Variants in UGT2B7 were not associated with altered O-glucuronidation of both 4-OHT and endoxifen, while UGT2B15 haplotypes had a modest effect on (E)-endoxifen plasma levels after adjustment for CYP2D6 genotypes. Our findings highlight the influence of UGT1A4 haplotypes on tamoxifen disposition in Asian breast cancer patients, while genetic variants in UGT2B7 and UGT2B15 appear to be of minor importance.

Hepatic glucuronidation of 4-tert-octylphenol in humans: inter-individual variability and responsible UDP-glucuronosyltransferase isoforms

4-tert-Octylphenol (4-tOP) is an endocrine-disrupting chemical. It is mainly metabolized into glucuronide by UDP-glucuronosyltransferase (UGT) enzymes in humans. The purpose of this study was to assess inter-individual variability in and the possible roles of UGT isoforms in hepatic 4-tOP glucuronidation in the humans. 4-tOP glucuronidation activities in the liver microsomes and recombinant UGTs of humans were assessed at broad substrate concentrations, and kinetics were analyzed. Correlation analyses between 4-tOP and diclofenac or 4-hydroxybiphenyl activities in pooled and individual human liver microsomes were also performed. Typical CL_int values were 17.8 mL/min/mg protein for the low type, 25.2 mL/min/mg protein for the medium type, and 47.7 mL/min/mg protein for the high type. Among the recombinant UGTs (13 isoforms) examined, UGT2B7 and UGT2B15 were the most active of catalyzing 4-tOP glucuronidation. Although the K _m values of UGT2B7 and UGT2B15 were similar (0.36 and 0.42 µM, respectively), the CL_int value of UGT2B7 (6.83 mL/min/mg protein) >UGT2B15 (2.35 mL/min/mg protein). Strong correlations were observed between the glucuronidation activities of 4-tOP and diclofenac (a probe for UGT2B7) or 4-hydroxybiphenyl (a probe for UGT2B15) with 0.79-0.88 of Spearman correlation coefficient (r _s) values. These findings demonstrate that 4-tOP glucuronidation in humans is mainly catalyzed by hepatic UGT2B7 and UGT2B15, and suggest that these UGT isoforms play important and characteristic roles in the detoxification of 4-tOP.

UGT1A6- and UGT2B7-related valproic acid pharmacogenomics according to age groups and total drug concentration levels

AIM

The role of UGT1A6 and UGT2B7 polymorphisms and the impact of total drug plasma concentration in valproic acid (VPA) pharmacogenomics.

PATIENTS & METHODS

A total of 134 Greek patients were recruited (76 adults). Patients were genotyped for UGT1A6 19T>G, 541A>G and 552A>C and UGT2B7 802T>C polymorphisms. Patients' demographic and clinical data were registered. Natural logarithm of concentration-to-dose ratio (CDR) was also calculated as the final outcome.

RESULTS

No significant genotype-related differences in VPA metabolism were noted among various subgroups. An increased lnCDR ratio was noted in children patients compared with adults suggesting increased metabolic capability in younger ages.

CONCLUSION

UGT1A6 and UGT2B7 genotypes were not related to significant changes in VPA metabolism, even after controlling for total drug concentration levels. Younger ages were associated with increased VPA clearance rate.

Human Genetic Variability Contributes to Postoperative Morphine Consumption

High interindividual variability in postoperative opioid consumption is related to genetic and environmental factors. We tested the association between morphine consumption, postoperative pain, and single nucleotide polymorphisms (SNPs) within opioid receptor μ 1 (OPRM1), catechol-O-methyltransferase (COMT), uridine diphosphate glucose-glucuronosyltransferase-2B7, and estrogen receptor (ESR1) gene loci to elucidate genetic prediction of opioid consumption. We analyzed 20 SNPs in 201 unrelated Caucasian patients who underwent abdominal surgery and who were receiving postoperative patient-controlled analgesia-administered morphine. Morphine consumption and pain intensity were dependent variables; age and sex were covariates. A haplotype of 7 SNPs in OPRM1 showed significant additive effects on opioid consumption (P = .007); a linear regression model including age and 9 SNPs in ESR1, OPRM1, and COMT explained the highest proportion of variance of morphine consumption (10.7%; P = .001). The minimal model including 3 SNPs in ESR1, OPRM1, and COMT explained 5% of variance (P = .007). We found a significant interaction between rs4680 in COMT and rs4986936 in ESR1 (P = .007) on opioid consumption. SNPs rs677830 and rs540825 of OPRM1 and rs9340799 of ESR1 were nominally associated with pain Numeric Rating Scale scores. Combinations of genetic variants within OPRM1, COMT, and ESR1 better explain variability in morphine consumption than single genetic variants. Our results contribute to the development of genetic markers and statistical models for future diagnostic tools for opioid consumption/efficacy.

PERSPECTIVE

This article presents the efforts dedicated to detect correlations between the genetic polymorphisms and the clinical morphine effect self-administered by patients using a patient-controlled analgesia pump after major surgery. The clinical effect is expressed in terms of morphine consumption and pain scores. REGISTERED ON CLINICALTRIALS.GOV: NCT01233752.

The pharmacogenetics of opioid therapy in the management of postpartum pain: a systematic review

AIMS

Opioids are commonly prescribed for postpartum pain. Yet, providing adequate pain relief, while ensuring that the mother and her breastfeeding infant are protected from adverse events can be challenging. The objective of this systematic review was to identify the role of opioid pharmacogenetics in analgesia and adverse events among patients being treated for postpartum pain, along with their breastfeeding infants.

METHODS

A comprehensive search of the literature was conducted in seven databases on June 3-4, 2015. Two reviewers independently screened studies for eligibility, extracted data and evaluated study quality using the Newcastle-Ottawa Scale.

RESULTS

Among the 2082 papers retrieved from the search, 17 were included in the review. These 17 papers consisted of various study designs, opioids, polymorphisms and patient outcomes. This systematic review reveals that CYP2D6, OPRM1 A118G, UGT2B7 C802T and ABCB1 G2677AT may contribute to postpartum analgesia or adverse events.

CONCLUSION

These findings may assist in personalizing care for patients receiving opioids during the postpartum period.

Effect of UGT2B7 -900G>A (-842G>A; rs7438135) on morphine glucuronidation in preterm newborns: results from a pilot cohort

AIM

Assess association between UGT2B7 polymorphism -900G>A (rs7438135, also known as -842G>A) with morphine kinetics in preterm newborns undergoing mechanical ventilation.

MATERIALS & METHODS

Thirty-four infants were enrolled in a randomized clinical trial and allocated to rapid sequence intubation with remifentanil (1 µg/kg) or morphine (0.3 mg/kg). The latter group was included in our study.

RESULTS

Morphine plasma concentrations at 20 min post intubation were associated with postnatal age (p=0.017) and UGT2B7 -900G>A (p=0.036). UGT2B7 -900A allele carriers (n=13) had lower morphine levels compared with UGT2B7 -900G/G patients (n=2). Morphine-3-glucuronide and morphine-6-glucuronide plasma concentrations were only found to be associated with gestational and postnatal age. However, -900A allele carriers had a higher morphine-3-glucuronide:morphine metabolic ratio compared with patients genotyped as -900G/G (p=0.005), as determined by linear regression.

CONCLUSION

Our small pilot study illustrates that in addition to gestational and postnatal age, the UGT2B7 -900G>A polymorphism significantly alters morphine pharmacokinetics in preterm infants.

In vitro glucuronidation of aprepitant: a moderate inhibitor of UGT2B7

1. Aprepitant, an oral antiemetic, commonly used in the prevention of chemotherapy-induced nausea and vomiting, is primarily metabolized by CYP3A4. Aprepitant glucuronidation has yet to be evaluated in humans. The contribution of human UDP-glucuronosyltransferase (UGT) isoforms to the metabolism of aprepitant was investigated by performing kinetic studies, inhibition studies and correlation analyses. In addition, aprepitant was evaluated as an inhibitor of UGTs. 2. Glucuronidation of aprepitant was catalyzed by UGT1A4 (82%), UGT1A3 (12%) and UGT1A8 (6%) and Kms were 161.6 ± 15.6, 69.4 ± 1.9 and 197.1 ± 28.2 µM, respectively. Aprepitant glucuronidation was significantly correlated with both UGT1A4 substrates anastrazole and imipramine (rs = 0.77, p < 0.0001 for both substrates; n = 44), and with the UGT1A3 substrate thyroxine (rs = 0.58, p < 0.0001; n = 44). 3. We found aprepitant to be a moderate inhibitor of UGT2B7 with a Ki of ∼10 µM for 4-MU, morphine and zidovudine. Our results suggest that aprepitant can alter clearance of drugs primarily eliminated by UGT2B7. Given the likelihood for first-pass metabolism by intestinal UGT2B7, this is of particular concern for oral aprepitant co-administered with oral substrates of UGT2B7, such as zidovudine and morphine.

Associations of UDP-glucuronosyltransferases polymorphisms with mycophenolate mofetil pharmacokinetics in Chinese renal transplant patients

AIM

To evaluate the effects of UDP-glucuronosyltransferases (UGTs) polymorphisms on the pharmacokinetics of the immunosuppressant mycophenolate mofetil (MMF) in Chinese renal transplant recipients.

METHODS

A total of 127 renal transplant patients receiving MMF were genotyped for polymorphisms in UGT1A9 -1818T>C, I399C>T, -118T9/10, -440C>T, -331T>C, UGT2B7 IVS1+985A>G, 211G>T, -900A>G, UGT1A8 518C>G and UGT1A7 622T>C. The plasma concentrations of the MMF active moiety mycophenolic acid (MPA) and main metabolite 7-O-MPA-glucuronide (MPAG) were analyzed using HPLC. Univariate and multivariate analyses were used to assess the effects of UGT-related gene polymorphisms on MPA pharmacokinetics.

RESULTS

The dose-adjusted MPA AUC0-12 h of the patients with the UGT2B7 IVS1+985AG genotype was 48% higher than that of the patients with the IVS1+985AA genotype, which could explain 11.2% of the inter-individual variation in MPA pharmacokinetics. The dose-adjusted MPAG AUC0-12 h of the patients with the UGT1A7 622CC and UGT1A9 -440CT/-331TC genotypes, respectively, was significantly higher than that of the patients with 622T homozygotes and -440C/-331T homozygotes. Furthermore, the genotypes UGT1A9 -1818T>C and UGT1A8 518C>G were associated with a low dose-adjusted MPAG AUC0-12 h.

CONCLUSION

The UGT2B7 11+985A>G genotype is associated with the pharmacokinetics of MPA in Chinese renal transplant patients, which demonstrates the usefulness of this SNP for individualizing MMF dosing.

Evaluation of the interindividual human variation in bioactivation of methyleugenol using physiologically based kinetic modeling and Monte Carlo simulations

The present study aims at predicting the level of formation of the ultimate carcinogenic metabolite of methyleugenol, 1'-sulfooxymethyleugenol, in the human population by taking variability in key bioactivation and detoxification reactions into account using Monte Carlo simulations. Depending on the metabolic route, variation was simulated based on kinetic constants obtained from incubations with a range of individual human liver fractions or by combining kinetic constants obtained for specific isoenzymes with literature reported human variation in the activity of these enzymes. The results of the study indicate that formation of 1'-sulfooxymethyleugenol is predominantly affected by variation in i) P450 1A2-catalyzed bioactivation of methyleugenol to 1'-hydroxymethyleugenol, ii) P450 2B6-catalyzed epoxidation of methyleugenol, iii) the apparent kinetic constants for oxidation of 1'-hydroxymethyleugenol, and iv) the apparent kinetic constants for sulfation of 1'-hydroxymethyleugenol. Based on the Monte Carlo simulations a so-called chemical-specific adjustment factor (CSAF) for intraspecies variation could be derived by dividing different percentiles by the 50th percentile of the predicted population distribution for 1'-sulfooxymethyleugenol formation. The obtained CSAF value at the 90th percentile was 3.2, indicating that the default uncertainty factor of 3.16 for human variability in kinetics may adequately cover the variation within 90% of the population. Covering 99% of the population requires a larger uncertainty factor of 6.4. In conclusion, the results showed that adequate predictions on interindividual human variation can be made with Monte Carlo-based PBK modeling. For methyleugenol this variation was observed to be in line with the default variation generally assumed in risk assessment.

Polymorphisms and haplotypes of the UDP-glucuronosyltransferase 2B7 gene promoter

Identification of functional polymorphisms in the UDP-glucuronosyltransferase 2B7 (UGT2B7) gene predicting interpatient variability in the glucuronidation of drugs that are primarily metabolized by UGT2B7 has been the subject of many studies. These studies have shown linkage disequilibrium (LD) covering the region from -2 kb to 16 kb of the UGT2B7 gene. We identified three novel single-nucleotide polymorphisms (SNPs) and extended this LD in the 5'-upstream direction to cover an additional nine prevalent polymorphisms in the distal -2600- to -4000-base pair (bp) promoter. We further showed complete LD between these distal promoter SNPs and the SNP (802C>T) in exon 2 in a panel of 26 livers. Because of this LD, we showed that all of the 23 prevalent polymorphisms in the 4-kb UGT2B7 promoter are linked together, defining two major haplotypes (i.e., I and II). The addition of the minor allele of a rare polymorphism and allele exchanges between haplotypes I and II generated subhaplotypes of I and II. We demonstrated a higher promoter activity of haplotype II over haplotype I, and this higher activity was abolished by an A-to-G change at a single SNP (-900A>G). This mutation changed a consensus activating protein-1 (AP-1) site (TGAGTCA) as occurred in haplotype II to a mutated AP-1 site (TGAGTCG) as occurred in haplotype I. Finally, we showed that the previously reported Alu element resides exclusively in haplotype I and is a highly conserved CG-rich Alu Y element.

Influence of uridine diphosphate-glucuronyltransferase 2B7 (UGT2B7) variants on postoperative buprenorphine analgesia

BACKGROUND

Genetic factors are known to influence individual differences in pain and sensitivity to analgesics. Different genetic polymorphisms in opioid-metabolizing enzymes that can affect the analgesic response to opioids have been proposed. This study investigates a possible difference in the response to postoperative buprenorphine analgesia related to the presence of different isoforms (cytosine or thymine substitution at nucleotide 802) of UGT2B7 gene.

METHODS

Transdermal buprenorphine was administered to 91 patients who underwent muscle-sparing thoracotomy. UGT2B7 polymorphism at locus C802T (His268Tyr) was detected using a PCR Taqman-based procedure. The severity of postoperative pain at rest and during coughing or deep inspiration was assessed by visual analog scale score after surgery. Hospital stay and perioperative opioid consumption were collected.

RESULTS

Genotype frequencies were 18.4% for UGT2B7*1/*1, 52.9% for UGT2B7*1/*2, and 28.7% for UGT2B7*2/*2. VAS pain scores at rest were statistically similar among the groups except at 24, 60, and 120 hours (UGT2B7*2/*2 genotype showing higher pain scores). Patients with the UGT2B7*2/*2 genotype showed higher VAS scores triggered by coughing after the 48 hours (P < 0.05). In addition, patients with this genotype reported a higher prevalence of severe pain after 48 postoperative hours (P < 0.05). Thirty-eight percent of patients carrying genotype UGT2B7*2/*2 experienced severe pain in a final survey vs. 17% in the group with UGT2B7*1/*1 (P = 0.36).

CONCLUSIONS

The presence of the SNP 802C>T UGT2B7 (UGT2B7*2/*2) is associated with a worse analgesic response to transdermal buprenorphine in the postoperative period of thoracic surgery.

Analgesia and central side-effects: two separate dimensions of morphine response

AIMS

To present a statistical model for defining interindividual variation in response to morphine and to use this model in a preliminary hypothesis-generating multivariate genetic association study.

METHODS

Two hundred and sixty-four cancer patients taking oral morphine were included in a prospective observational study. Pain and morphine side-effect scores were examined using principal components analysis. The resulting principal components were used in an exploratory genetic association study of single nucleotide polymorphisms across the genes coding for the three opioid receptors, OPRM1, OPRK1 and OPRD1. Associations in multivariate models, including potential clinical confounders, were explored.

RESULTS

Two principal components corresponding to residual pain and central side-effects were identified. These components accounted for 42 and 18% of the variability in morphine response, respectively, were independent of each other and only mildly correlated. The genetic and clinical factors associated with these components were markedly different. Multivariate regression modelling, including clinical and genetic factors, accounted for only 12% of variability in residual pain on morphine and 3% of variability in central side-effects.

CONCLUSIONS

Although replication is required, this data-driven analysis suggests that pain and central side-effects on morphine may be two separate dimensions of morphine response. Larger study samples are necessary to investigate potential genetic and clinical associations comprehensively.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Pharmacogenomics of opioids and perioperative pain management

Inadequate pain relief and adverse effects from analgesics remain common in children and adults during the perioperative period. Opioids are the most commonly used analgesics in children and adults to treat perioperative pain. Narrow therapeutic index and a large interpatient variability in response to opioids are clinically significant, with inadequate pain relief at one end of the spectrum and serious side effects, such as respiratory depression and excessive sedation due to relative overdosing, at the other end. Personalizing analgesia during the perioperative period attempts to maximize pain relief while minimizing adverse events from therapy. While various factors influence response to treatment among surgical patients, age, sex, race and pharmacogenetic differences appear to play major roles in predicting outcome. Genetic factors include a subset of genes that modulate the proteins involved in pain perception, pain pathway, analgesic metabolism (pharmacokinetics), transport and receptor signaling (pharmacodynamics). While results from adult genetic studies can provide direction for pediatric studies, they have limited direct applicability, as children's genetic predispositions to analgesic response may be influenced by developmental and behavioral components, altered sensitivity to analgesics and variation in gene-expression patterns. We have reviewed the available evidence on improving and personalizing pain management with opioids and the significance of individualizing analgesia, in order to maximize analgesic effect with minimal adverse effects with opioids. While the early evidence on individual genotype associations with pain, analgesia and opioid adverse outcome are promising, the large amount of conflicting data in the literature suggests that there is a need for larger and more robust studies with appropriate population stratification and consideration of nongenetic and other genetic risk factors. Although the clinical evidence and the prospect of being able to provide point-of-care genotyping to enable clinicians to deliver personalized analgesia for individual patients is still not available, positioning our research to identify all possible major genetic and nongenetic risk factors of an individual patient, advancing less expensive point-of-care genotyping technology and developing easy-to-use personalized clinical decision algorithms will help us to improve current clinical and economic outcomes associated with pain and opioid pain management.

Differences between opioids: pharmacological, experimental, clinical and economical perspectives

Clinical studies comparing the response and side effects of various opioids have not been able to show robust differences between drugs. Hence, recommendations of the regulatory authorities have been driven by costs with a general tendency in many countries to restrict physician's use of opioids to morphine. Although this approach is recognized as cost-effective in most cases there is solid evidence that, on an individual patient basis, opioids are not all equal. Therefore it is important to have an armamentarium of strong analgesics in clinical practice to ensure a personalized approach in patients who do not respond to standard treatment. In this review we highlight differences between opioids in human studies from a pharmacological, experimental, clinical and health economics point of view. We provide evidence that individuals respond differently to opioids, and that general differences between classes of opioids exist. We recommend that this recognition is used to individualize treatment in difficult cases allowing physicians to have a wide range of treatment options. In the end this will reduce pain and side effects, leading to improved quality of life for the patient and reduce the exploding pain related costs.

Variability in UDP-glucuronosyltransferase genes and morphine metabolism: observations from a cross-sectional multicenter study in advanced cancer patients with pain

OBJECTIVE

The objective of the present study was to determine whether genetic variability in UDP-glucuronosyltransferase (UGT) genes, together with clinical factors, contribute to variability in morphine glucuronide (M6G and M3G) to morphine serum concentration ratios in patients with advanced cancer receiving chronic morphine therapy.

MATERIALS AND METHODS

A total of 41 polymorphisms and predicted haplotypes in the UGT2B7, UGT1A1, and UGT1A8 genes were analyzed in 759 patients who were recruited from the European Pharmacogenetic Opioid Study and received chronic morphine therapy by the oral route (n=635) or parenterally (n=124). The administration groups were analyzed separately by multiple linear regression analyses.

RESULTS

Two haplotypes in UGT1A1/UGT1A8 were weak predictors of reduced M6G/morphine and M3G/morphine serum ratios after oral administration (false discovery rate-corrected P-values<0.1). No effect of genotype was seen in the parenteral group. Of the clinical variables (age, sex, BMI, renal function, Karnofsky performance status, and presence of liver metastases), renal function was the major contributor to variation in serum concentration ratios. Concomitant administration of paracetamol predicted significantly higher morphine metabolic ratios after oral administration of morphine (false discovery rate-corrected P-values<2.1E-12). The regression models explained about 35% of the total variability in the data.

CONCLUSION

Genetic variation in the UGT genes together with clinical factors influence morphine metabolic ratios in patients with advanced cancer disease and who are scheduled with oral morphine. This information may be included in future research that develop and test new classification systems for opioid treatment in patients with advanced cancer.

Profiling serum bile acid glucuronides in humans: gender divergences, genetic determinants, and response to fenofibrate

Glucuronidation, catalyzed by UDP-glucuronosyltransferase (UGT) enzymes detoxifies cholestatic bile acids (BAs). We aimed at i) characterizing the circulating BA-glucuronide (-G) pool composition in humans, ii) evaluating how sex and UGT polymorphisms influence this composition, and iii) analyzing the effects of lipid-lowering drug fenofibrate on the circulating BA-G profile in 300 volunteers and 5 cholestatic patients. Eleven BA-Gs were determined in pre- and post-fenofibrate samples. Men exhibited higher BA-G concentrations, and various genotype/BA-G associations were discovered in relevant UGT genes. The chenodeoxycholic acid-3G concentration was associated with the UGT2B7 802C>T polymorphism. Glucuronidation assays confirmed the predominant role of UGT2B7 and UGT1A4 in CDCA-3G formation. Fenofibrate exposure increased the serum levels of 5 BA-G species, including CDCA-3G, and up-regulated expression of UGT1A4, but not UGT2B7, in hepatic cells. This study demonstrates that fenofibrate stimulates BA glucuronidation in humans, and thus reduces bile acid toxicity in the liver.

Pharmacogenetics of opiates in clinical practice: the visible tip of the iceberg

Opioids are the cornerstone of analgesic therapy and are used as a substitution therapy for opiate addiction. Interindividual variability in response to opioids is a significant challenge in the management of pain and substitution. Therefore, treatment with opioids requires a careful individualization of dosage to achieve an appropriate balance of efficacy and adverse effects and, consequently, avoid toxicity, particularly respiratory depression, sedation and for some, cardiac ventricular fibrillations. Many studies have investigated the association between genetic factors and the variability of response to opioids. Variants in genes encoding proteins implied in opioid pharmacokinetics (absorption, distribution, metabolism, excretion and toxicity), together with those implied in opioids direct and indirect pharmacodynamics (genes of opioid receptors and monoaminergic systems), are the most studied. Many association studies have not been replicated. The purpose of this article is to summarize pharmacogenetic data associated with some opioids frequently encountered in managed care settings.