Polymorphisme génétique et interactions médicamenteuses : leur importance dans le traitement de la douleur

Tapentadol Versus Tramadol: A Narrative and Comparative Review of Their Pharmacological, Efficacy and Safety Profiles in Adult Patients

We conducted a narrative review of the literature to compare the pharmacological, efficacy and safety profiles of tapentadol and tramadol, and to assess the clinical interest of tapentadol in adult patients. Tapentadol and tramadol share a mixed mechanism of action, including both mu-agonist and monoaminergic properties. Tapentadol is approximately two to three times more potent than tramadol and two to three times less potent than morphine. It has no identified analgesically active metabolite and is not significantly metabolised by cytochrome P450 enzymes, thus overcoming some limitations of tramadol, including the potential for pharmacokinetic drug-drug interactions and interindividual variability due to genetic polymorphisms of cytochrome P450 enzymes. The toxicity profiles of tramadol and tapentadol are similar; however tapentadol is likely to result in less exposure to serotoninergic adverse effects (nausea, vomiting, hypoglycaemia) but cause more opioid adverse effects (constipation, respiratory depression, abuse) than tramadol. The safety of tapentadol in real-world conditions remains poorly documented, particularly in at-risk patient subgroups and also in the ability to assess the risk associated with its residual serotonergic activity (serotonin syndrome, seizures). Because of an earlier market introduction, more real-world safety data are available for tramadol, including data from at-risk patient subgroups. The level of evidence on the efficacy of both tramadol and tapentadol for the treatment of chronic pain is globally low. The trials published to date show overall that tapentadol does not provide a clinically significant analgesic improvement compared to existing treatments, for which the safety profile is much better known. In conclusion, tapentadol is not a first-line opioid but represents an additional analgesic in the therapeutic choices, which some patients may benefit from after careful examination of their clinical situation, co-morbidities and co-medications.

CYP2D6 pharmacogenetic and oxycodone pharmacokinetic association study in pediatric surgical patients

AIM

Oxycodone is partly metabolized to the active metabolite oxymorphone by hepatic CYP2D6 in the liver. Significant genetic variability in CYP2D6 activity affects oxymorphone formation. This study aimed to associate CYP2D6 genotype and oxycodone's metabolism.

METHODS

30 children were administered oral oxycodone postoperatively. Plasma levels of oxycodone and oxymorphone, and CYP2D6 genotype were analyzed. CYP2D6 genotype and oxycodone metabolism phenotype were determined based on CYP2D6 total activity score (TAS) and metabolism phenotype: poor metabolizer (PM), intermediate metabolizer (IM), extensive metabolizer (EM) or ultrarapid metabolizer (UM).

RESULTS

Compared with PM/IM subjects, significantly greater oxymorphone exposure was seen in EM subjects (p = 0.02 for C_max, p = 0.016 for AUC_0-6 and p = 0.026 for AUC_0-24). Similarly, higher TAS value was found to be associated with greater oxymorphone exposure. Higher conversion of oxycodone to oxymorphone was observed in EM subjects compared with PM/IM subjects (p = 0.0007 for C_max, p = 0.001 for AUC_0-6 and p = 0.004 for AUC_0-24).

CONCLUSION

CYP2D6 phenotypes explain metabolism of oxycodone in children, and oxymorphone exposure is higher in CYP2D6 EM phenotype. Further studies are needed to predict the occurrence of adverse event and tailor oxycodone dose for a specific CYP2D6 phenotype.

Influence of UGT2B7, CYP3A4, and OPRM1 Gene Polymorphisms on Transdermal Buprenorphine Pain Control in Patients with Critical Lower Limb Ischemia Awaiting Revascularization

BACKGROUND

Pain control in critical limb ischemia (CLI) varies considerably between individuals.

OBJECTIVE

To evaluate pharmacogenetically the response to transdermal buprenorphine (BUP-TTS) in patients with CLI who are awaiting revascularization.

METHODS

One hundred and seven patients with CLI were treated with BUP-TTS. The following were analyzed: (1) pain perception (visual analog scale (VAS) before and 4 days after treatment) and (2) genetics: glucuronosyltransferase (UGT2B7), cytochrome (CYP3A4), and μ-opioid receptor (OPRM1) gene polymorphisms.

RESULTS

Ninety-three patients completed the study. The VAS score by the fourth day of analgesia dropped from 6.82 to 3.38 (P < 0.05). The analgesic response to BUP-TTS was greater in men than in women (P = 0.019). Patients who were AA homozygotes for the CYP3A4 gene showed the best response to analgesic treatment (P = 0.003). The combination of the CYP3A4 gene with UGT2B7 or OPRM1 was favorable to the effect of the CYP3A4 gene (P = 0.045 and P = 0.026, respectively). The combination of UGT2B7 with OPRM1 was ineffective (P = 0.648). The 3 polymorphisms together had no effect on response to treatment (P = 0.461).

CONCLUSIONS

BUP-TTS is efficacious in the control of pain in patients with CLI. The homozygous AA carriers of the CYP3A4 gene respond better to treatment with BUP-TTS.

Effect of the CYP2D6 gene polymorphism on postoperative analgesia of tramadol in Han nationality nephrectomy patients

OBJECTIVE

Tramadol is a synthetic opioid which has analgesic efficacy in the postoperative pain. It is metabolized by polymorphic enzyme cytochrome P450 (CYP2D6). Patients with different CYP2D6 genotypes would have different responses to tramadol in pain relief. The CYP2D6*10 allele is the most common allele in a Chinese population. The aim of this study was to evaluate whether the different CYP2D6*10 genotypes have an effect on the postoperative tramadol analgesia in the Chinese population after elective nephrectomy.

METHODS

One hundred and twenty patients after performed elective nephrectomy were enrolled in this study after being approved by the local Ethics Committee. The patients were given patient-controlled analgesia (PCA) which included 10 mg/ml tramadol after receiving a loading dose of 100 mg tramadol and 1 mg granisetron intravenously. Blood samples were collected after induction of anesthesia. The CYP2D6*10 polymorphism was analyzed by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). According to the results, the patients were divided into three groups (CYP2D6*1/*1, n = 33; CYP2D6*1/*10, n = 28; CYP2D6*10/*10, n = 50). The total consumption of tramadol, visual analogue scale (VAS) score, and PCA control times among the three genotype groups for 2, 4, 24, 48, and 72 h after operation were compared.

RESULTS

Nine out of 120 patients were dropped out of the study; 111 patients completed the study. The frequency of CYP2D6*10 allele was 57.7%. The demographic data among the three groups were comparable. The consumption of tramadol, patient self-control times of pump, and VAS score in CYP2D6*10/*10 group were significantly higher than that in CYP2D6*1/*1 or CYP2D6*1/*10 group at 2 and 4 h (P < 0.05), while it did not differ between CYP2D6*1/*1 and CYP2D6*1/*10 group (P > 0.05). There was no difference in the incidence of nausea and vomiting among the three groups (P > 0.05). No sever apnea was recorded in these groups.

CONCLUSIONS

Different CYP2D6*10 genotypes have an influence on the analgesic effect of tramadol in Han nationality patients after elective nephrectomy.

The serotonin transporter gene polymorphism is associated with the susceptibility and the pain severity in idiopathic trigeminal neuralgia patients

BACKGROUND

To investigate the possible association between the serotonin transporter gene (5-HTTLPR) and rs 25531 polymorphism and the susceptibility and the pain severity in Trigeminal Neuralgia patients.

METHODS

A total of 244 TN patients and 280 age and sex matched healthy volunteer were recruited. 5-HTTLPR and rs 25531 genotyping were performed. All patients received the carbamazepine treatment and the treatment response was evaluated at 6 months.

RESULTS

The genotype distribution of 5-HTTLPR between TN patients and controls were significantly different. The TN Patients had a higher prevalence of short-short genotype than controls. The short-short genotype carriers are also significantly associated with higher pain severity and poorer carbamazepine treatment response compared to the long-long genotype carriers. In contrast, the rs 25531 polymorphism was not associated with the susceptibility to TN, neither with the pain severity and the treat response to carbamazepine.

CONCLUSION

The 5-HTTLPR polymorphism is associated with the susceptibility to TN and pain severity of TN.

New approaches to the pharmacotherapy of neuropathic pain

Pain is one of the most debilitating symptoms that presents with neuropathy. Neuropathic pain syndrome is a challenge to treat and, even with appropriate evidence-based treatment, only a 40% reduction of symptoms can be achieved in approximately half of patients. Furthermore, efficient doses are often difficult to obtain because of adverse effects. These observations underline that the treatment of neuropathic pain is still an unmet medical need. New approaches to the pharmacotherapy of neuropathy embrace different lines of work, including a fundamental mechanism-based approach, a clinical mechanism-based approach and an evidence-based approach. Moreover, interindividual variability in drug response, and genetic polymorphism in particular, is an emerging aspect to consider. Together with reviewing recent evidence-based guidelines as well as briefly discussing genetic polymorphisms that may influence the individual responses to treatments, this article will focus on what a mechanism-based approach is bringing to the clinical setting, on the perspective in fundamental research and on the difficulty of bridging the gap between fundamental notions and positive clinical outcomes.

Pain, analgesia and genetics

OBJECTIVES

In the clinical setting, there is marked intersubject variability in the intensity of pain reported by patients with apparently similar pain states, as well as widely differing analgesic dosing requirements between individuals to produce satisfactory pain relief with tolerable side-effects. Genetic and environmental factors as well as their interaction are implicated, and these are discussed in this review.

KEY FINDINGS

Pioneering work undertaken in mice more than a decade ago, showed a strong genetic contribution to levels of nociception/hypersensitivity as well as levels of antinociception produced by commonly available analgesic agents. To date more than 300 candidate 'pain' genes have been identified as potentially contributing to heritable differences in pain sensitivity and analgesic responsiveness in animals and humans, with this information available in a publicly accessible database http://www.jbldesign.com/jmogil/enter.html. Since then, many genetic association studies have been conducted in humans to investigate the possibility that single nucleotide polymorphisms (SNPs) in an individual gene may explain drug inefficacy or excessive toxicity experienced by a small subset of the whole population who have the rare allele for a particular SNP.

SUMMARY

Despite the fact that SNPs in more than 20 genes that affect pain sensitivity or contribute to interindividual variability in responses to analgesic medications have been identified in the human genome, much of the data is conflicting. Apart from deficiencies in the design and conduct of human genetic association studies, recent research from other fields has implicated epigenetic mechanisms that facilitate dynamic gene-environment communication, as a possible explanation.

Effect of CYP3A4*1G on the fentanyl consumption for intravenous patient-controlled analgesia after total abdominal hysterectomy in Chinese Han population

WHAT IS KNOWN AND OBJECTIVE

  Clinical investigations into postoperative intravenous patient-controlled analgesia (PCA) have indicated interindividual differences in fentanyl consumption. Cytochrome P450 3A4 (CYP3A4) is the main metabolism enzyme of fentanyl, and single nucleotide polymorphisms within the CYP3A4 gene may contribute to the variability of fentanyl analgesic efficacy. The aim of this study was to investigate whether the most common genetic variation in Chinese, CYP3A4*1G, has an impact on the fentanyl consumption for intravenous PCA in Chinese Han women undergone abdominal total hysterectomy.

METHODS

A total of 79 female patients (American Society of Anesthesiologist physical status I or II) scheduled to undergo elective abdominal total hysterectomy were enrolled. All patients received combined spinal-epidural anaesthesia with bupivacaine. Intravenous fentanyl PCA was provided postoperatively for satisfactory analgesia. The doses of fentanyl consumption were recorded 2, 4, 24 and 48 h after the initiation of PCA postoperatively. Pain at rest and adverse effects were measured with rating scales. CYP3A4*1G was screened by means of direct sequencing and further confirmed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS AND DISCUSSION

Forty-six patients were GG homozygotes, 27 patients were GA heterozygotes, and six patients were AA homozygotes, respectively. The distribution of the CYP3A4*1G allele was consistent with Hardy-Weinberg equilibrium (P>0·05). At 2 and 4 h, the doses of fentanyl required for patients with GA/AA genotypes were 80·0 (45·0, 112·5) μg and 120·0 (80, 173·8)μg, respectively, and significantly lower than those for GG homozygotes [91·3 (80·0, 125·0) μg and 169·0 (112·5, 226·3) μg, respectively, P<0·05]. There was trend of decreasing fentanyl consumption at 24 and 48h in patients with GA/AA genotypes, relative to GG homozygotes, but the difference was not statistical significant (P>0·05).

WHAT IS NEW AND CONCLUSIONS

CYP3A4*1G has an impact on the analgesic effect of fentanyl in Chinese Han subjects. Further validation of our results in a well-powered study would be helpful.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety

BACKGROUND AND PURPOSE

The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored.

EXPERIMENTAL APPROACH

We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed.

KEY RESULTS

CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers.

CONCLUSIONS AND IMPLICATIONS

The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

The effects of CYP2D6 and CYP3A activities on the pharmacokinetics of immediate release oxycodone

BACKGROUND AND PURPOSE

There is high interindividual variability in the activity of drug-metabolizing enzymes catalysing the oxidation of oxycodone [cytochrome P450 (CYP) 2D6 and 3A], due to genetic polymorphisms and/or drug-drug interactions. The effects of CYP2D6 and/or CYP3A activity modulation on the pharmacokinetics of oxycodone remains poorly explored.

EXPERIMENTAL APPROACH

A randomized crossover double-blind placebo-controlled study was performed with 10 healthy volunteers genotyped for CYP2D6 [six extensive (EM), two deficient (PM/IM) and two ultrarapid metabolizers (UM)]. The volunteers randomly received on five different occasions: oxycodone 0.2 mg x kg(-1) and placebo; oxycodone and quinidine (CYP2D6 inhibitor); oxycodone and ketoconazole (CYP3A inhibitor); oxycodone and quinidine+ketoconazole; placebo. Blood samples for plasma concentrations of oxycodone and metabolites (oxymorphone, noroxycodone and noroxymorphone) were collected for 24 h after dosing. Phenotyping for CYP2D6 (with dextromethorphan) and CYP3A (with midazolam) were assessed at each session.

KEY RESULTS

CYP2D6 activity was correlated with oxymorphone and noroxymorphone AUCs and C(max) (-0.71 < Spearman correlation coefficient rhos < -0.92). Oxymorphone C(max) was 62% and 75% lower in PM than EM and UM. Noroxymorphone C(max) reduction was even more pronounced (90%). In UM, oxymorphone and noroxymorphone concentrations increased whereas noroxycodone exposure was halved. Blocking CYP2D6 (with quinidine) reduced oxymorphone and noroxymorphone C(max) by 40% and 80%, and increased noroxycodone AUC(infinity) by 70%. Blocking CYP3A4 (with ketoconazole) tripled oxymorphone AUC(infinity) and reduced noroxycodone and noroxymorphone AUCs by 80%. Shunting to CYP2D6 pathway was observed after CYP3A4 inhibition.

CONCLUSIONS AND IMPLICATIONS

Drug-drug interactions via CYP2D6 and CYP3A affected oxycodone pharmacokinetics and its magnitude depended on CYP2D6 genotype.

Analgesic efficacy of perioperative use of vedaprofen, tramadol or their combination in cats undergoing ovariohysterectomy

The analgesic efficacy of tramadol and/or vedaprofen was evaluated in cats submitted for elective ovariohysterectomy, using a randomised double blind placebo controlled design. Forty adult female cats (3.0±0.32 kg; 1.8±0.7 years) were distributed into four groups. Vedaprofen PO (0.5 mg/kg), tramadol SC (2 mg/kg), both, or placebo was administered 1 h before surgery and every 24 and 8 h, respectively, for 72 h after surgery. Pain score evaluated by interactive visual analogue and composite pain score and hyperalgesia by the von Frey filament test were recorded at 1, 2, 4, 6, 8, 12, 24, 28, 32, 48, 52, 56, 72, 96 h and on the 7th day after surgery. Animals treated with combined vedaprofen and tramadol treatment did not need rescue analgesia, did not develop hyperalgesia, and their serum cortisol concentrations and pain scores were lower than placebo until 24 and 72 h after surgery, respectively. Combined vedaprofen and tramadol treatment provided more effective postoperative analgesia and prevented hyperalgesia than when used on their own. Multimodal technique is a superior method of treating pain after feline ovariohysterectomy. This work also provides evidence for the benefits of analgesia for up to 3 days following ovariohysterectomy.

Pharmacogenetics of analgesics: toward the individualization of prescription

The use of analgesics is based on the empiric administration of a given drug with clinical monitoring for efficacy and toxicity. However, individual responses to drugs are influenced by a combination of pharmacokinetic and pharmacodynamic factors that can sometimes be regulated by genetic factors. Whereas polymorphic drug-metabolizing enzymes and drug transporters may affect the pharmacokinetics of drugs, polymorphic drug targets and disease-related pathways may influence the pharmacodynamic action of drugs. After a usual dose, variations in drug toxicity and inefficacy can be observed depending on the polymorphism, the analgesic considered and the presence or absence of active metabolites. For opioids, the most studied being morphine, mutations in the ABCB1 gene, coding for P-glycoprotein (P-gp), and in the µ-opioid receptor reduce morphine potency. Cytochrome P450 (CYP) 2D6 mutations influence the analgesic effect of codeine and tramadol, and polymorphism of CYP2C9 is potentially linked to an increase in nonsteroidal anti-inflammatory drug-induced adverse events. Furthermore, drug interactions can mimic genetic deficiency and contribute to the variability in response to analgesics. This review summarizes the available data on the pharmacokinetic and pharmacodynamic consequences of known polymorphisms of drug-metabolizing enzymes, drug transporters, drug targets and other nonopioid biological systems on central and peripheral analgesics.

Concentrations of tramadol and O-desmethyltramadol enantiomers in different CYP2D6 genotypes

The influence of CYP2D6 genotype and CYP2D6 inhibitors on enantiomeric plasma levels of tramadol and O-desmethyltramadol as well as response to tramadol was investigated. One hundred and seventy-four patients received one hundred intravenous tramadol 3 mg/kg for postoperative analgesia. Blood samples drawn 30, 90, and 180 min after administration were analyzed for plasma concentrations of the enantiomers (+)-, (-)tramadol and (+)-, (-)O-desmethyltramadol by liquid chromatography-tandem mass spectrometry. Different CYP2D6 genotypes displaying zero (poor metabolizer (PM)), one (heterozygous individual (HZ)/intermediate metabolizer (IM)), two extensive metabolizer (EM), and three (ultra rapid metabolizer (UM)) active genes were compared. Concentrations of O-desmethyltramadol differed in the four genotype groups. Median (1/3 quartile) area under the concentration-time curves for (+)O-desmethyltramadol were 0 (0/11.4), 38.6 (15.9/75.3), 66.5 (17.1/118.4), and 149.7 (35.4/235.4) ng x h/ml for PMs, HZ/IMs, EMs, and UMs (P<0.001). Comedication with CYP2D6 inhibitors decreased (+) O-desmethyltramadol concentrations (P<0.01). In PMs, non-response rates to tramadol treatment increased fourfold compared with the other genotypes (P<0.001). In conclusion, CYP2D6 genotype determined concentrations of O-desmethyltramadol enantiomers and influenced efficacy of tramadol treatment.

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.

Effect of the CYP2D6*10 C188T polymorphism on postoperative tramadol analgesia in a Chinese population

OBJECTIVE

The CYP2D6*10 allele is the most common allele with a frequency ranging from 51.3 to 70% and correlated with a significantly reduced metabolic activity in a Chinese population. The aim of the present study was to investigate whether the CYP2D6*10 allele has an impact on the postoperative analgesia effect of tramadol in Chinese patients recovering from major abdominal surgery.

METHODS

A prospective study design was used and 70 gastric cancer patients recovering from gastrectomy were enrolled. After receiving a loading dose i.v., patients could self-administer doses of the drug combination (10 mg/ml tramadol plus 0.3 mg/ml metoclopramide) via patient-controlled analgesia (PCA). Blood samples were collected after induction of anesthesia. The CYP2D6*10 C188T polymorphism was analyzed by means of polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP). Demographic data among groups with different genotypes were analyzed using analysis of variance. The total consumption of tramadol between the three genotype groups for 48 h was compared.

RESULTS

The allele frequency of CYP2D6*10 is 52.4%; patients were categorized into three groups according to the CYP2D6 genotype: patients without CYP2D6*10 (group I, n=17), patients heterozygous for CYP2D6*10 (group II, n=26), and patients homozygous for CYP2D6*10 (group III, n=20). The demographic data among the three groups were comparable. The total consumption of tramadol for 48 h in group III was significantly higher than that in groups I and II, while it did not differ between groups I and II.

CONCLUSIONS

This study indicates that the CYP2D6*10 allele has significant impact on analgesia with tramadol in a Chinese population. Pharmacogenetics may explain some of the varying responses to pain medication in postoperative patients.