Impact of CYP2D6 genetic polymorphism on tramadol pharmacokinetics and pharmacodynamics

From Drug Discovery to Drug Approval: A Comprehensive Review of the Pharmacogenomics Status Quo with a Special Focus on Egypt

Pharmacogenomics (PGx) is the hope for the full optimization of drug therapy while minimizing the accompanying adverse drug events that cost billions of dollars annually. Since years before the century, it has been known that inter-individual variations contribute to differences in specific drug responses. It is the bridge to what is well-known today as "personalized medicine". Addressing the drug's pharmacokinetics and pharmacodynamics is one of the features of this science, owing to patient characteristics that vary on so many occasions. Mainly in the liver parenchymal cells, intricate interactions between the drug molecules and enzymes family of so-called "Cytochrome P450" occur which hugely affects how the body will react to the drug in terms of metabolism, efficacy, and safety. Single nucleotide polymorphisms, once validated for a transparent and credible clinical utility, can be used to guide and ensure the succession of the pharmacotherapy plan. Novel tools of pharmacoeconomics science are utilized extensively to assess cost-effective pharmacogenes preceding the translation to the bedside. Drug development and discovery incorporate a drug-gene perspective and save more resources. Regulations and laws shaping the clinical PGx practice can be misconceived; however, these pre-/post approval processes ensure the product's safety and efficacy. National and international regulatory agencies seek guidance on maintaining conduct in PGx practice. In this patient-centric era, social and legal considerations manifest in a way that makes them unavoidable, involving patients and other stakeholders in a deliberate journey toward utmost patient well-being. In this comprehensive review, we contemporarily addressed the scientific leaps in PGx, along with various challenges that face the proper implementation of personalized medicine in Egypt. These informative insights were drawn to serve what the Egyptian population, in particular, would benefit from in terms of knowledge and know-how while maintaining the latest global trends. Moreover, this review is the first to discuss various modalities and challenges faced in Egypt regarding PGx, which we believe could be used as a pilot piece of literature for future studies locally, regionally, and internationally.

Neuropathic pain: Mechanisms and therapeutic strategies

The physiopathology and neurotransmission of pain are of an owe inspiring complexity. Our ability to satisfactorily suppress neuropathic or other forms of chronic pain is limited. The number of pharmacodynamically distinct and clinically available medications is low and the successes achieved modest. Pain Medicine practitioners are confronted with the ethical dichotomy imposed by Hippocrates: On one hand the mandate of primum non nocere, on the other hand, the promise of heavenly joys if successful divinum est opus sedare dolorem. We briefly summarize the concepts associated with nociceptive pain from nociceptive input (afferents from periphery), modulatory output [descending noradrenergic (NE) and serotoninergic (5-HT) fibers] to local control. The local control is comprised of the "inflammatory soup" at the site of pain origin and synaptic relay stations, with an ATP-rich environment promoting inflammation and nociception while an adenosine-rich environment having the opposite effect. Subsequently, we address the transition from nociceptor pain to neuropathic pain (independent of nociceptor activation) and the process of sensitization and pain chronification (transient pain progressing into persistent pain). Having sketched a model of pain perception and processing we attempt to identify the sites and modes of action of clinically available drugs used in chronic pain treatment, focusing on adjuvant (co-analgesic) medication.

Human variability in polymorphic CYP2D6 metabolism: Implications for the risk assessment of chemicals in food and emerging designer drugs

The major human cytochrome P450 CYP2D6 isoform enzyme plays important roles in the liver and in the brain with regards to xenobiotic metabolism. Xenobiotics as CYP2D6 substrates include a whole range of pharmaceuticals, pesticides and plant alkaloids to cite but a few. In addition, a number of endogenous compounds have been shown to be substrates of CYP2D6 including trace amines in the brain such as tyramine and 5-methoxytryptamine as well as anandamide and progesterone. Because of the polymorphic nature of CYP2D6, considerable inter-phenotypic and inter-ethnic differences in the pharmaco/toxicokinetics (PK/TK) and metabolism of CYP2D6 substrates exist with potential consequences on the pharmacology and toxicity of chemicals. Here, large extensive literature searches have been performed to collect PK data from published human studies for a wide range of pharmaceutical probe substrates and investigate human variability in CYP2D6 metabolism. The computed kinetic parameters resulted in the largest open source database, quantifying inter-phenotypic differences for the kinetics of CYP2D6 probe substrates in Caucasian and Asian populations, to date. The database is available in supplementary material (CYPD6 DB) and EFSA knowledge junction (DOI to added). Subsequently, meta-analyses using a hierarchical Bayesian model for markers of chronic oral exposure (oral clearance, area under the plasma concentration time curve) and acute oral exposure (maximum plasma concentration (Cmax) provided estimates of inter-phenotypic differences and CYP2D6-related uncertainty factors (UFs) for chemical risk assessment in Caucasian and Asian populations classified as ultra-rapid (UM), extensive (EMs), intermediate (IMs) and poor metabolisers (PMs). The model allowed the integration of inter-individual (i.e. inter-phenotypic and inter-ethnic), inter-compound and inter-study variability together with uncertainty in each PK parameter. Key findings include 1. Higher frequencies of PMs in Caucasian populations compared to Asian populations (>8% vs 1-2%) for which EM and IM were the most frequent phenotype. 2. Large inter-phenotypic differences in PK parameters for Caucasian EMs (coefficients of variation (CV) > 50%) compared with Caucasian PMs and Asian EMs and IMs (i.e CV < 40%). 3. Inter-phenotypic PK differences between EMs and PMs in Caucasian populations increase with the quantitative contribution of CYP2D6 for the metabolism (fm) for a range of substrates (fm_CYP2D6 range: 20-95% of dose) (range: 1-54) to a much larger extent than those for Asian populations (range: 1-4). 4. Exponential meta-regressions between Fm_CYP2D6 in EMs and inter-phenotypic differences were also shown to differ between Caucasian and Asian populations as well as CYP2D6-related UFs. Finally, implications of these results for the risk assessment of food chemicals and emerging designer drugs of public health concern, as CYP2D6 substrates, are highlighted and include the integration of in vitro metabolism data and CYP2D6-variability distributions for the development of quantitative in vitro in vivo extrapolation models.

Reviewing pharmacogenetics to advance precision medicine for opioids

BACKGROUND

Adequate opioid prescribing is critical for therapeutic success of pain management. Despite the widespread use of opioids, optimized opioid therapy remains unresolved with risk of accidental lethal overdosing. With the emergence of accumulating evidence linking genetic variation to opioid response, pharmacogenetic based treatment recommendations have been proposed.

OBJECTIVE

The aim of this review is to evaluate pharmacogenetic evidence and provide an overview on genes involved in the pharmacokinetics and pharmacodynamics of opioids.

METHODS

For this review, a systematic literature search of published articles was used in PubMed®, with no language restriction and between the time period of January 2000 to December 2020. We reviewed randomized clinical studies, study cohorts and case reports that investigated the influence of genetic variants on selected opioid pharmacokinetics and pharmacodynamics. In addition, we reviewed current CPIC clinical recommendations for pharmacogenetic testing.

RESULTS

Results of this review indicate consistent evidence supporting the association between selected genetic variants of CYP2D6 for opioid metabolism. CPIC guidelines include recommendations that indicate the avoidance of tramadol use, in addition to codeine, in CYP2D6 poor metabolizers and ultrarapid metabolizers, and to monitor intermediate metabolizers for less-than-optimal response. While there is consistent evidence for OPRM1 suggesting increased postoperative morphine dosing requirements in A118G G-allele carriers, the clinical relevance remains limited.

CONCLUSION

There is emerging evidence of clinical relevance of CYP2D6 and, to a lesser extent, OPRM1 polymorphism in personalized opioid drug dosing. As a result, first clinics have started to implement pharmacogenetic guidelines for CYP2D6 and codeine.

New Insights on Tramadol and Immunomodulation

PURPOSE OF REVIEW

Opioids are administered to cancer patients although concerns have been raised that they may promote tumour growth or metastasis owing to their ability to suppress anti-cancer immunity. Tramadol has been reported to preserve or promote the immune response and may therefore be preferred to other opioids in cancer patients. We reviewed the literature documenting the immunomodulatory effects of tramadol.

RECENT FINDINGS

Recent clinical evidence appears to confirm that tramadol possesses anti-inflammatory properties, and preserves some signalling cascades of the immune system relevant to anti-cancer defence. Tramadol is reported to promote or preserve immunity including natural killer cell activity which is important in anti-cancer defences.

A review on tramadol toxicity: mechanism of action, clinical presentation, and treatment

Aims

As an analgesic that acts upon the central nervous system (CNS), tramadol has gained popularity in treating moderate to severe pain. Recently, it has been increasingly reported as a drug of misuse with intentional overdoses or intoxications. This review focuses on tramadol intoxication in humans and its effects on different systems.

Subject and method

This narrative review provides a comprehensive view of the pharmacokinetics, mechanism of action, and incidence of tramadol toxicity with an in-depth look at its side effects. In addition, the main approaches to the management of tramadol poisoning are described.

Results

Tramadol poisoning can affect multiple organ systems: gastrointestinal, central nervous system (seizure, CNS depression, low-grade coma, anxiety, and over time anoxic brain damage), cardiovascular system (palpitation, mild hypertension to life-threatening complications such as cardiopulmonary arrest), respiratory system, renal system (renal failure with higher doses of tramadol intoxication), musculoskeletal system (rhabdomyolysis), endocrine system (hypoglycemia), as well as, cause serotonin syndrome. Seizure, a serious nervous disturbance, is more common in tramadol intoxication than with other opioids. Fatal tramadol intoxications are uncommon, except in ingestion cases concurrent with other medications, particularly CNS depressants, most commonly benzodiazepines, and ethanol.

Conclusion

With the increasing popularity of tramadol, physicians must be aware of its adverse effects, substantial abuse potential, and drug interactions, to weigh its risk–benefit ratio for pain management. Alternative therapies might be considered in patients with a previous overdose history to reduce risks for adverse outcomes.

Pharmacokinetic profile of injectable tramadol in the koala (Phascolarctos cinereus) and prediction of its analgesic efficacy

Tramadol is used as an analgesic in humans and some animal species. When tramadol is administered to most species it undergoes metabolism to its main metabolites M1 or O-desmethyltramadol, and M2 or N-desmethyltramadol, and many other metabolites. This study describes the pharmacokinetic profile of tramadol when a single subcutaneous bolus of 2 mg/kg was initially administered to two koalas. Based on the results of these two koalas, subsequently 4 mg/kg as a single subcutaneous injection, was administered to an additional four koalas. M1 is recognised as an active metabolite and has greater analgesic activity than tramadol, while M2 is considered inactive. A liquid chromatography assay to quantify tramadol, M1 and M2 in koala plasma was developed and validated. Liquid chromatography-mass spectrometry confirmed that M1 had been identified. Additionally, the metabolite didesmethyltramadol was identified in chromatograms of two of the male koalas. When 4 mg/kg tramadol was administered, the median half-life of tramadol and M1 were 2.89 h and 24.69 h, respectively. The M1 plasma concentration remained well above the minimally effective M1 plasma concentration in humans (approximately 36 ng/mL) over 12 hours. The M1 plasma concentration, when tramadol was administered at 2 mg/kg, did not exceed 36 ng/mL at any time-point. When tramadol was administered at 2 mg/kg and 4 mg/kg the area under the curve M1: tramadol ratios were 0.33 and 0.50, respectively. Tramadol and M1 binding to plasma protein were determined using thawed, frozen koala plasma and the mean binding was 20% and 75%, respectively. It is concluded that when tramadol is administered at 4 mg/kg as a subcutaneous injection to the koala, it is predicted to have some analgesic activity.

Impact of CYP2D6 activity and cachexia progression on enantiomeric alteration of plasma tramadol and its demethylated metabolites and their relationships with central nervous system symptoms in head and neck cancer patients

This study aimed to evaluate the influence of CYP2D6 activity and cachexia progression on the enantiomeric alteration of plasma tramadol and its demethylated metabolites in head and neck cancer patients. Fifty-three head and neck cancer patients receiving oral tramadol were enrolled. The plasma concentrations of tramadol, O-desmethyltramadol (ODT) and N-desmethyltramadol (NDT) enantiomers were determined. The CYP2D6 activity score (AS) and degree of cachexia progression were assessed according to genotype and the Glasgow Prognostic Score (GPS), respectively. The enantiomeric ratio of NDT was (+)-form dominant in all patients. CYP2D6 AS had negative correlations with the plasma concentrations of (+)-NDT and (-)-NDT. The plasma concentrations of (+)-tramadol and (+)-ODT were higher in patients with GPS 1 or 2 than in those with GPS 0. Lower metabolic ratios to NDT enantiomers were observed in patients with GPS 1 or 2. In patients with GPS 1 or 2, the plasma (-)-tramadol was associated with the incidence of central nervous system symptoms. In conclusion, CYP2D6 AS partially explained the contribution of CYP2D6 activity to plasma tramadol and its demethylated metabolite enantiomers. Additionally, cachexia progression elevated the plasma (+)-tramadol and (+)-ODT levels through the reduction of N-demethylation of (+)-tramadol.

Clinical Tolerability and Safety of Tramadol in Hospitalized Patients

Tramadol is a schedule IV, monoaminergic and μ-opioid-receptor analgesic with unique pharmacology properties. Though it is well established and widely utilized, there is little guidance on tramadol's place in therapy, including tolerability, safety and monitoring guidelines. Retrospective chart review of 250 patients who received oral tramadol during their hospitalization from January 1, 2018 to December 31, 2018. Of the 250 patients, 10.8% had cancer as their primary diagnosis while 8.8% were admitted for hematologic reasons. 79.1% of patients had acute pain. Palliative care consult or ICU admission resulted in significant discontinuation of tramadol (p < 0.05 odds ratio 6.88, 2.39). There was no significant relationship of hypoglycemia when evaluating days on tramadol, total number of doses on tramadol, and MEDD start and end (p = 0.36, 0.88, 0.15, 0.23 consecutively). The longer that patients were on tramadol and the more doses they received during their inpatient stay, the greater risk of a severe drug-drug interaction (p < 0.05; R 0.29). In hospitalized patients, the risk of major and severe drug-drug interactions with tramadol increased with dose and duration. Hospital medicine, bone marrow transplant, and emergency medicine teams predominantly used tramadol.

Genetics and Gender in Acute Pain and Perioperative Opioid Analgesia

Experimental and clinical acute pain research in relation to biological sex and genetics started in the 1980s. Research methods became more powerful and sensitive with the advancement in affordable gene sequencing methods and high-throughput genetic assays. Decades of research has identified several potential pharmaceutical targets, providing insights into future research direction, and understanding of acute pain and opioid analgesic effects in the clinical setting. However, there is insufficient evidence to make generalized recommendations for using genetic tests for clinical practice of acute pain management.

Physician's role in prescribing opioids in developing countries

In developed countries, addressing the growing opioid addiction epidemic is focused on preventive measures, developing better overdose-reversal medications and designing newer strategies to treat addiction. Primary prescribers of the therapeutic use of opioids might play a definite role in the aetiology of the epidemics. Developing countries could be affected by similar issues; however, given that no updated statistics are available, it is possible that their populations undergo problems similar to those for which current data is available. Concerns have arisen regarding synthetic opioid tramadol which, given its fast and potent analgesic effects, low cost and easy availability is widely prescribed. A debate remains as to whether tramadol induces addictive effects like those of stronger analogues such as oxycodone or fentanyl. Here we present a case of tramadol dependence in an Ecuadorian patient and find that substance abuse can occur in normal individuals affected by chronic pain, otherwise treatable with standard methods.

Pharmacokinetics of Tramadol and Celecoxib in Japanese and Caucasian Subjects Following Administration of Co-Crystal of Tramadol-Celecoxib (CTC): A Randomised, Open-Label Study

BACKGROUND AND OBJECTIVES

Co-Crystal of Tramadol-Celecoxib (CTC) is a first-in-class active pharmaceutical ingredient (API-API) co-crystal of rac-tramadol.HCl and celecoxib in a 1:1 molecular ratio (100 mg CTC: 44 mg rac-tramadol.HCl and 56 mg celecoxib). Tramadol and celecoxib pharmacokinetics are modified after CTC administration versus administration of reference products. This randomised, open-label, crossover, phase 1 study assessed CTC pharmacokinetics, dose proportionality, safety and tolerability in Japanese and Caucasian subjects.

METHODS

CTC (100, 150 and 200 mg) was administered orally to healthy Japanese/Caucasian subjects. Tramadol, O-desmethyltramadol and celecoxib plasma concentrations were determined pre-dose and up to 48 h post-dose. Maximum observed plasma concentration (Cmax), and area under the plasma concentration-time curve from dosing to last measurable concentration (AUCt) and from dosing extrapolated to infinity (AUC∞) were evaluated. Dose proportionality was assessed in a dose-adjusted bioavailability analysis of variance and in a power model. Inter-cohort comparability of pharmacokinetic exposure was confirmed if the ratio (Japanese cohort/Caucasian cohort) of geometric least-squares means and corresponding 90% confidence intervals were 80-125%. Post hoc weight-adjusted comparability analyses were performed. Safety was assessed throughout.

RESULTS

Sixty subjects (21 males/9 females per cohort) were randomised; 57 completed the study. Cohorts were age and BMI matched; there were expected inter-cohort weight differences. Exposure to each analyte increased in both cohorts with increasing CTC dose. Tramadol's pharmacokinetic exposure was comparable between cohorts after adjusting for body weight; the pharmacokinetic exposure of O-desmethyltramadol and celecoxib was increased in Japanese subjects.

CONCLUSIONS

Differences in pharmacokinetics were not sufficient to suggest that CTC dose adjustment is required in Japanese subjects.

CLINICAL TRIAL REGISTRATION

EudraCT: 2015-003071-29.

A Systematic Review of Laboratory Evidence for the Abuse Potential of Tramadol in Humans

Background: Tramadol is an opioid-analgesic that has shown epidemiological evidence of abuse. This review evaluates the evidence for tramadol abuse potential in humans. Methods: A systematic literature search for human abuse liability examinations of tramadol was conducted in September 2018 and yielded 13 total studies. Studies were all within-subject, double-blind, placebo-controlled human laboratory comparisons of tramadol to opioid comparators. Results are organized based upon the route of tramadol administration (oral, parenteral) and the participant population (persons with and without current opioid physical dependence). Outcomes were categorized into self-report ratings of positive and negative effects, observer-ratings of effects, time course of effects, likelihood tramadol was identified as an opioid, and tramadol self-administration. Results: Results indicated the relative abuse potential of tramadol was lower than the opioids to which it was compared. Tramadol produced highest positive effect ratings when administered orally to persons with no opioid physical dependence. Relative to other opioids, it produced substantial negative ratings, generally demonstrated a slower onset of effects, and was less likely to be identified by participants as an opioid, though it did produce a higher rate of self-administration relative to other opioids in the one study reporting that outcome. Results suggest that the abuse potential of tramadol is highest when it is administered orally to non-dependent individuals, and that it likely decreases as the dose increased and when it was administered parentally or to persons with opioid physical dependence. Conclusion: Taken together, individuals may be less likely than with other opioids to escalate tramadol doses, transition from oral to parenteral routes of administration, or continue using tramadol once opioid physical dependence develops. In that way, the human abuse potential of tramadol appears to be different from and lower than other opioid analgesic medications.

Tramadol Hydrochloride at Steady State Lacks Clinically Relevant QTc Interval Increases in Healthy Adults

We evaluated the effects of therapeutic and supratherapeutic doses of tramadol hydrochloride on the corrected QT (QTc) interval in healthy adults (aged 18‐55 years) in a randomized, phase I, double‐blind, placebo‐ and positive‐controlled, multiple‐dose, 4‐way crossover study. Participants were randomized to receive 1 of 4 treatments (A‐D), 1 each in 4 treatment periods (1‐4), separated by a washout period (7‐15 days). Treatment A comprised tramadol 400 mg (therapeutic dose) on days 1 through 3, tramadol 100 mg and moxifloxacin‐matched placebo on day 4, and placebo on all 4 days. Treatment B comprised tramadol 600 mg (supratherapeutic dose) on days 1 through 3, and tramadol 150 mg and moxifloxacin‐matched placebo on day 4. Treatment C comprised placebo on days 1 through 4 and moxifloxacin‐matched placebo on day 4. Treatment D comprised placebo on days 1 through 4 and moxifloxacin 400 mg on day 4. Of 68 participants enrolled, 57 (83.8%) completed the study. Both therapeutic and supratherapeutic doses of tramadol were shown to be noninferior to placebo regarding their effect on QTc prolongation. Sixty‐one of 68 (89.7%) participants reported at least 1 treatment‐emergent adverse event (mild); nausea was the most frequently reported treatment‐emergent adverse event. Summarizing, tramadol at doses up to 600 mg/day did not cause clinically relevant QTc interval prolongation in healthy adults.

Design and rational for the precision medicine guided treatment for cancer pain pragmatic clinical trial

INTRODUCTION

Pain is one of the most burdensome symptoms associated with cancer and its treatment, and opioids are the cornerstone of pain management. Opioid therapy is empirically selected, and patients often require adjustments in therapy to effectively alleviate pain or ameliorate adverse drug effects that interfere with quality of life. There are data suggesting CYP2D6 genotype may contribute to inter-patient variability in response to opioids through its effects on opioid metabolism. Therefore, we aim to determine if CYP2D6 genotype-guided opioid prescribing results in greater reductions in pain and symptom severity and interference with daily living compared to a conventional prescribing approach in patients with cancer.

METHODS

Patients with solid tumors with metastasis and a self-reported pain score ≥ 4/10 are eligible for enrollment and randomized to a genotype-guided or conventional pain management strategy. For patients in the genotype-guided arm, CYP2D6 genotype information is integrated into opioid prescribing decisions. Patients are asked to complete questionnaires regarding their pain, symptoms, and quality of life at baseline and 2, 4, 6, and 8 weeks after enrollment. The primary endpoint is differential change in pain severity by treatment strategy (genotype-guided versus conventional pain management). Secondary endpoints include change in pain and symptom interference with daily living.

CONCLUSION

Pharmacogenetic-guided opioid selection for cancer pain management has potential clinical utility, but current evidence is limited to retrospective and observational studies. Precision Medicine Guided Treatment for Cancer Pain is a pragmatic clinical trial that seeks to determine the utility of CYP2D6 genotype-guided opioid prescribing in patients with cancer.

When the Safe Alternative Is Not That Safe: Tramadol Prescribing in Children

Children represent a vulnerable population in which management of nociceptive pain is complex. Drug responses in children differ from adults due to age-related differences. Moreover, therapeutic choices are limited by the lack of indication for a number of analgesic drugs due to the challenge of conducting clinical trials in children. Furthermore the assessment of efficacy as well as tolerance may be complicated by children's inability to communicate properly. According to the World Health Organization, weak opioids such as tramadol and codeine, may be used in addition to paracetamol and ibuprofen for moderate nociceptive pain in both children and adults. However, codeine prescription has been restricted for the last 5 years in children because of the risk of fatal overdoses linked to the variable activity of cytochrome P450 (CYP) 2D6 which bioactivates codeine. Even though tramadol has been considered a safe alternative to codeine, it is well established that tramadol pharmacodynamic opioid effects, efficacy and safety, are also largely influenced by CYP2D6 activity. For this reason, the US Food and Drug Administration recently released a boxed warning regarding the use of tramadol in children. To provide safe and effective tramadol prescription in children, a personalized approach, with dose adaptation according to CYP2D6 activity, would certainly be the safest method. We therefore recommend this approach in children requiring chronic or recurrent nociceptive pain treatment with tramadol. In case of acute inpatients nociceptive pain management, prescribing tramadol at the minimal effective dose, in a child appropriate dosage form and after clear instructions are given to the parents, remains reasonable based on current data. In all other situations, morphine should be preferred for moderate to severe nociceptive pain conditions.

Efficacy of Tramadol Extended-Release for Opioid Withdrawal: A Randomized Clinical Trial

IMPORTANCE

Opioid use disorder (OUD) is a significant public health problem. Supervised withdrawal (ie, detoxification) from opioids using clonidine or buprenorphine hydrochloride is a widely used treatment.

OBJECTIVE

To evaluate whether tramadol hydrochloride extended-release (ER), an approved analgesic with opioid and nonopioid mechanisms of action and low abuse potential, is effective for use in supervised withdrawal settings.

DESIGN, SETTING, AND PARTICIPANTS

A randomized clinical trial was conducted in a residential research setting with 103 participants with OUD. Participants' treatment was stabilized with morphine, 30 mg, administered subcutaneously 4 times daily. A 7-day taper using clonidine (n = 36), tramadol ER (n = 36), or buprenorphine (n = 31) was then instituted, and patients were crossed-over to double-blind placebo during a post-taper period. The study was conducted from October 25, 2010, to June 23, 2015.

MAIN OUTCOMES AND MEASURES

Retention, withdrawal symptom management, concomitant medication utilization, and naltrexone induction. Results were analyzed over time and using area under the curve for the intention-to-treat and completer groups.

RESULTS

Of the 103 participants, 88 (85.4%) were men and 43 (41.7%) were white; mean (SD) age was 28.9 (10.4) years. Buprenorphine participants (28 [90.3%]) were significantly more likely to be retained at the end of the taper compared with clonidine participants (22 [61.1%]); tramadol ER retention was intermediate and did not differ significantly from that of the other groups (26 [72.2%]; χ2 = 8.5, P = .01). Time-course analyses of withdrawal revealed significant effects of phase (taper, post taper) for the Clinical Opiate Withdrawal Scale (COWS) score (taper mean, 5.19 [SE, .26]; post-taper mean, 3.97 [SE, .23]; F2,170 = 3.6, P = .03) and Subjective Opiate Withdrawal Scale (SOWS) score (taper mean,8.81 [SE, .40]; post-taper mean, 4.14 [SE, .30]; F2,170 = 15.7, P < .001), but no group effects or group × phase interactions. Analyses of area under the curve of SOWS total scores showed significant reductions (F2,159 = 17.7, P < .001) in withdrawal severity between the taper and post-taper periods for clonidine (taper mean, 13.1; post-taper mean, 3.2; P < .001) and tramadol ER (taper mean, 7.4; post-taper mean, 2.8; P = .03), but not buprenorphine (taper mean, 6.4; post-taper mean, 7.4). Use of concomitant medication increased significantly (F2,159 = 30.7,  P < .001) from stabilization to taper in the clonidine (stabilization mean, 0.64 [SE, .05]; taper mean, 1.54 [SE, .10]; P < .001) and tramadol ER (stabilization mean, 0.53 [SE, .05]; taper mean, 1.19 [SE, .09]; P = .003) groups and from stabilization to post taper in the buprenorphine group (stabilization mean, 0.46 [SE, .05] post-taper mean, 1.17 [SE, .09]; P = .006), suggesting higher withdrawal for those groups during those periods. Naltrexone initiation was voluntary and the percentage of participants choosing naltrexone therapy within the clonidine (8 [22.2%]), tramadol ER (7 [19.4%]), or buprenorphine (3 [9.7%]) groups did not differ significantly (χ2 = 2.5, P = .29).

CONCLUSIONS AND RELEVANCE

The results of this trial suggest that tramadol ER is more effective than clonidine and comparable to buprenorphine in reducing opioid withdrawal symptoms during a residential tapering program. Data support further examination of tramadol ER as a method to manage opioid withdrawal symptoms.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT01188421.

Tramadol for neuropathic pain in adults

BACKGROUND

This review is an update of a review of tramadol for neuropathic pain, published in 2006; updating was to bring the review in line with current standards. Neuropathic pain, which is caused by a lesion or disease affecting the somatosensory system, may be central or peripheral in origin. Peripheral neuropathic pain often includes symptoms such as burning or shooting sensations, abnormal sensitivity to normally painless stimuli, or an increased sensitivity to normally painful stimuli. Neuropathic pain is a common symptom in many diseases of the peripheral nervous system.

OBJECTIVES

To assess the analgesic efficacy of tramadol compared with placebo or other active interventions for chronic neuropathic pain in adults, and the adverse events associated with its use in clinical trials.

SEARCH METHODS

We searched CENTRAL, MEDLINE, and Embase for randomised controlled trials from inception to January 2017. We also searched the reference lists of retrieved studies and reviews, and online clinical trial registries.

SELECTION CRITERIA

We included randomised, double-blind trials of two weeks' duration or longer, comparing tramadol (any route of administration) with placebo or another active treatment for neuropathic pain, with subjective pain assessment by the participant.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality and potential bias. Primary outcomes were participants with substantial pain relief (at least 50% pain relief over baseline or very much improved on Patient Global Impression of Change scale (PGIC)), or moderate pain relief (at least 30% pain relief over baseline or much or very much improved on PGIC). Where pooled analysis was possible, we used dichotomous data to calculate risk ratio (RR) and number needed to treat for an additional beneficial outcome (NNT) or harmful outcome (NNH), using standard methods. We assessed the quality of the evidence using GRADE and created 'Summary of findings' tables.

MAIN RESULTS

We identified six randomised, double-blind studies involving 438 participants with suitably characterised neuropathic pain. In each, tramadol was started at a dose of about 100 mg daily and increased over one to two weeks to a maximum of 400 mg daily or the maximum tolerated dose, and then maintained for the remainder of the study. Participants had experienced moderate or severe neuropathic pain for at least three months due to cancer, cancer treatment, postherpetic neuralgia, peripheral diabetic neuropathy, spinal cord injury, or polyneuropathy. The mean age was 50 to 67 years with approximately equal numbers of men and women. Exclusions were typically people with other significant comorbidity or pain from other causes. Study duration for treatments was four to six weeks, and two studies had a cross-over design.Not all studies reported all the outcomes of interest, and there were limited data for pain outcomes. At least 50% pain intensity reduction was reported in three studies (265 participants, 110 events). Using a random-effects analysis, 70/132 (53%) had at least 50% pain relief with tramadol, and 40/133 (30%) with placebo; the risk ratio (RR) was 2.2 (95% confidence interval (CI) 1.02 to 4.6). The NNT calculated from these data was 4.4 (95% CI 2.9 to 8.8). We downgraded the evidence for this outcome by two levels to low quality because of the small size of studies and of the pooled data set, because there were only 110 actual events, the analysis included different types of neuropathic pain, the studies all had at least one high risk of potential bias, and because of the limited duration of the studies.Participants experienced more adverse events with tramadol than placebo. Report of any adverse event was higher with tramadol (58%) than placebo (34%) (4 studies, 266 participants, 123 events; RR 1.6 (95% CI 1.2 to 2.1); NNH 4.2 (95% CI 2.8 to 8.3)). Adverse event withdrawal was higher with tramadol (16%) than placebo (3%) (6 studies, 485 participants, 45 events; RR 4.1 (95% CI 2.0 to 8.4); NNH 8.2 (95% CI 5.8 to 14)). Only four serious adverse events were reported, without obvious attribution to treatment, and no deaths were reported. We downgraded the evidence for this outcome by two or three levels to low or very low quality because of small study size, because there were few actual events, and because of the limited duration of the studies.

AUTHORS' CONCLUSIONS

There is only modest information about the use of tramadol in neuropathic pain, coming from small, largely inadequate studies with potential risk of bias. That bias would normally increase the apparent benefits of tramadol. The evidence of benefit from tramadol was of low or very low quality, meaning that it does not provide a reliable indication of the likely effect, and the likelihood is very high that the effect will be substantially different from the estimate in this systematic review.

Tramadol with or without paracetamol (acetaminophen) for cancer pain

BACKGROUND

Tramadol is an opioid analgesic licensed for use in moderate to severe pain. It is considered as a low risk for abuse, so control regulations are not as stringent as for 'strong' opioids such as morphine. It has a potential role as a step 2 option of the World Health Organization (WHO) analgesic ladder.

OBJECTIVES

To assess the benefits and adverse effects of tramadol with or without paracetamol (acetaminophen) for cancer-related pain.

SEARCH METHODS

We searched the following databases using a wide range of search terms: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, and LILACS. We also searched three clinical trials registry databases. The date of the last search was 2 November 2016.

SELECTION CRITERIA

We selected studies that were randomised, with placebo or active controls, or both, and included a minimum of 10 participants per treatment arm. We were interested particularly in blinded studies, but also included open studies.We excluded non-randomised studies, studies of experimental pain, case reports, and clinical observations.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data using a standard form and checked for agreement before entry into Review Manager 5. We included information about the number of participants treated and demographic details, type of cancer, drug and dosing regimen, study design (placebo or active control) and methods, study duration and follow-up, analgesic outcome measures and results, withdrawals, and adverse events. We collated multiple reports of the same study, so that each study, rather than each report, was the unit of interest in the review. We assessed the evidence using GRADE and created a 'Summary of findings' table.The main outcomes of interest for benefit were pain reduction of 30% or greater and 50% or greater from baseline, participants with pain no worse than mild, and participants feeling much improved or very much improved.

MAIN RESULTS

We included 10 studies (12 reports) with 958 adult participants. All the studies enrolled participants with chronic malignant tumour-related pain who were experiencing pain intensities described as moderate to severe, with most experiencing at least 4/10 with current treatment. The mean ages were 59 to 70 years, with participants aged between 24 and 87 years. Study length ranged from one day to six months. Five studies used a cross-over design. Tramadol doses ranged from 50 mg as single dose to 600 mg per day; doses of 300 mg per day to 400 mg per day were most common.Nine studies were at high risk of bias for one to four criteria (only one high risk of bias for size). We judged all the results to be very low quality evidence because of widespread lack of blinding of outcome assessment, inadequately described sequence generation, allocation concealment, and small numbers of participants and events. Important outcomes were poorly reported. There were eight different active comparators and one comparison with placebo. There was little information available for any comparison and no firm conclusions could be drawn for any outcome.Single comparisons of oral tramadol with codeine plus paracetamol, of dihydrocodeine, and of rectal versus oral tramadol provided no data for key outcomes. One study used tramadol combined with paracetamol; four participants received this intervention. One study compared tramadol with flupirtine - a drug that is no longer available. One study compared tramadol with placebo and a combination of cobrotoxin, tramadol, and ibuprofen, but the dosing schedule poorly explained.Two studies (191 participants) compared tramadol with buprenorphine. One study (131 participants) reported a similar proportion of no or mild pain at 14 days.Three studies (300 participants) compared tramadol with morphine. Only one study, combining tramadol, tramadol plus paracetamol, and paracetamol plus codeine as a single weak-opioid group reported results. Weak opioid produced reduction in pain of at least 30% from baseline in 55/117 (47%) participants, compared with 91/110 (82%) participants with morphine. Weak opioid produced reduction in pain of at least 50% in 49/117 (42%) participants, compared with 83/110 (75%) participants with morphine.There was no useful information for any other outcome of benefit or harm.

AUTHORS' CONCLUSIONS

There is limited, very low quality, evidence from randomised controlled trials that tramadol produced pain relief in some adults with pain due to cancer and no evidence at all for children. There is very low quality evidence that it is not as effective as morphine. This review does not provide a reliable indication of the likely effect. The likelihood that the effect will be substantially different is very high. The place of tramadol in managing cancer pain and its role as step 2 of the WHO analgesic ladder is unclear.

Serotonin-norepinephrine reuptake inhibitors and the influence of binding affinity (Ki) on analgesia

WHAT IS KNOWN AND OBJECTIVE

Serotonin-norepinephrine reuptake inhibitors (SNRIs) are commonly used for various psychiatric conditions and neuropathic pain syndromes. SNRIs inhibit the reuptake of serotonin (5-HT) and norepinephrine (NE); however, NE reuptake inhibition is thought to be the primary mediator for their analgesic effect.

COMMENT

Key differences in pharmacodynamics and receptor affinities exist between SNRIs. The selectivity for each monoamine differs among SNRIs based on the agent's affinity and activity at the monoamine reuptake transporter. We review differences in receptor affinities and monoamine selectivity among SNRIs and the corresponding clinical impact.

WHAT IS NEW AND CONCLUSION

The varying selectivity for 5-HT and NE among the SNRIs may help explain the therapeutic dosing required for neuropathic pain as well as dose-related adverse effects. It is important to understand the pharmacologic differences among SNRIs, in addition to the data from clinical trials, to guide their safe and effective use.

Neuropathic Pain due to Small Fiber Neuropathy in Aging: Current Management and Future Prospects

Over the last 10 years, the diagnosis small fiber neuropathy (SFN) has gained recognition worldwide. Patients often suffer from severe neuropathic pain that may be difficult to treat. A substantial subset of patients with SFN is aged 65 years or older, and these patients often exhibit comorbidities and usage of multiple drugs, making neuropathic pain treatment more challenging. In this review, we highlight relevant pathophysiological aspects and discuss currently used therapeutic strategies for neuropathic pain. Possible pitfalls in neuropathic pain treatment in the elderly will be underlined.

Pharmacogenomics and Opioid Analgesics: Clinical Implications

Variation exists in patient response on analgesic treatment in terms of efficacy and safety. This variation may be in part explained by pharmacogenomics. This paper aimed to review data on pharmacogenomics of opioid analgesics focusing on the effect of genetic variation on the efficacy and safety of these agents. Current evidence suggests that pharmacogenomics contribute to variation in efficacy and safety of opioids. However, most data come from case control studies and case reports. In addition, a recognized drawback in the field of pharmacogenomics is the common occurrence of false positive association between polymorphisms and the investigated outcome. Prospective studies are needed to further elucidate the clinical implications of available data as well as to define the guidelines for the clinical application of pharmacogenomic data. Furthermore, basic research should focus on the identification of biologically meaningful polymorphisms enabling a hypothesis with biological plausibility driven research in the field of pharmacogenomics of analgesics. Moreover, the publication of relevant negative results should be favoured.

Tramadol half life is dose dependent in overdose

Background

Tramalol overdose is disproportionately more common in Iran. In recent years, Tramadol overdose has become one of the most common causes of poisoning admissions to emergency departments in this country. To the best of our knowledge, there is little or no information regarding the toxicokinetic properties of Tramadol such as its half life. Given the fact that poisoning management should be based on the toxicokinetic of substances, we aimed at investigating the half life of Tramadol in man as a critical toxicokinetic variable in overdose.

Methods

Blood samples of each patient were collected on admission and repeated later. Plasma was harvested after separation from blood cells by centrifugation and quantified using HPLC method. Calculations were performed on Tramadol blood concentration quantities.

Findings

Demographic: Most of cases were men (81.81%). Mean (Standard Deviation (SD), min-max) age was 23 (8.142, 17-40). Serum Tramadol levels: Mean (SD, min-max) first Tramadol concentration was 786.91 (394.53, 391-1495). Mean (SD, min-max) second Tramadol concentration was 433.09 (269.63, 148-950). Mean (SD, min-max) of Tramadol half life was calculated as 9.24 hour (2.310, 4.99-13.45) Associations: Half life was associated with higher concentrations (r=0.708 Sig=0.015).

Conclusion

We report the mean half life of tramadol in overdose to be 9.24 hours which is remarkably higher than that measured in previous pharmacokinetic studies. We also concluded that Tramadol half life is dose dependent in overdose which may explain the further consequences of severe overdoses.

Identification of bioactivating enzymes involved in the hydrolysis of laninamivir octanoate, a long-acting neuraminidase inhibitor, in human pulmonary tissue

Laninamivir octanoate (LO) is an octanoyl ester prodrug of the neuraminidase inhibitor laninamivir. After inhaled administration, LO exhibits clinical efficacy for both treatment and prophylaxis of influenza virus infection, resulting from hydrolytic bioactivation into its pharmacologically active metabolite laninamivir in the pulmonary tissue. In this study, we focused on the identification of LO-hydrolyzing enzymes from human pulmonary tissue extract using proteomic correlation profiling-a technology integration of traditional biochemistry and proteomics. In a single elution step by gel-filtration chromatography, LO-hydrolyzing activity was separated into two distinct peaks, designated as peak I and peak II. By mass spectrometry, 1160 and 1003 proteins were identified and quantitated for peak I and peak II, respectively, and enzyme candidates were ranked based on the correlation coefficient between the enzyme activity and the proteomic profiles. Among proteins with a high correlation value, S-formylglutathione hydrolase (esterase D; ESD) and acyl-protein thioesterase 1 (APT1) were selected as the most likely candidates for peak I and peak II, respectively, which was confirmed by LO-hydrolyzing activity of recombinant proteins. In the case of peak II, LO-hydrolyzing activity was completely inhibited by treatment with a specific APT1 inhibitor, palmostatin B. Moreover, immunohistochemical analysis revealed that both enzymes were mainly localized in the pulmonary epithelia, a primary site of influenza virus infection. These findings demonstrate that ESD and APT1 are key enzymes responsible for the bioactivation of LO in human pulmonary tissue.

Codeine-related adverse drug reactions in children following tonsillectomy: a prospective study

OBJECTIVES/HYPOTHESIS

To prospectively determine factors associated with codeine's adverse drug reactions (ADRs) at home in a large homogenous population of children undergoing outpatient tonsillectomy.

STUDY DESIGN

Prospective, genotype blinded, observational study with a single group and repeated ADR measures documented by parents at home.

METHODS

A total of 249 children 6 to 15 years of age scheduled for tonsillectomy were enrolled. The primary outcome was number of daily codeine-related ADRs. We examined the number and type of ADR by race and by days and further modeled factors potentially associated with ADR risk in a subcohort of white children. Sedation following a dose of codeine was a secondary outcome measure. Parents recorded their children's daily ADRs and sedation scores during postoperative days (POD) 0 to 3 at home.

RESULTS

Diaries were returned for 134 children, who were given codeine. A total of 106 (79%) reported at least one ADR. The most common ADRs were nausea, lightheadedness/dizziness for white children and nausea, and vomiting for African American children. In a subcohort of white children ≤ 45 kg, increased ADR risk was associated with the presence of one or more full function CYP2D6 alleles (P < 0.001), POD (P < 0.001), and sex (P = 0.027). Increased pain intensity (P = 0.009) and PODs 0 and 1 (P = 0.001) contributed to a higher sedation risk. Neither obstructive apnea nor predicted CYP2D6 phenotype were associated with sedation risk.

CONCLUSIONS

Our results provide evidence that multiple factors are associated with codeine-related ADRs and support the FDA recommendation to avoid codeine's routine use following tonsillectomy in children.

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.

CYP2D6*2 Polymorphism as a Predictor of Failed Outpatient Tramadol Therapy in Postherpetic Neuralgia Patients

Human cytochrome P4502D6 (CYP2D6) gene is highly polymorphic, leading to wide interindividual ethnic differences in CYP2D6-mediated drug metabolism. Its activity ranges from complete deficiency to excessive activity, potentially causing toxicity of the medication or therapeutic failure with recommended drug dosages. The aim of the study was to find the association of CYP2D6*2 polymorphisms with demographic characters (age, sex, and weight), pain intensity scales [numerical rating scale (NRS) sleep, global perceived effect (GPE)], and adverse drug effects in postherpetic neuralgia (PHN) patients receiving tramadol. The study comprised 246 patients [including 123 nonresponders (NRs) and 123 responders (Rs)] with PHN undergoing analgesic treatment at the pain clinic, Out Patient Department, University College of Medical Sciences, Guru Teg Bahadur Hospital, Delhi, India. Patients with any history of diabetes mellitus, human immunodeficiency virus, malignancy, hematological or liver disease, psychiatric illness, alcohol abuse, and tramadol sensitivity were excluded from the study. The NRSs of (resting and movement), NRS-sleep, and GPE were evaluated by the treating physician. Adverse drug effects during the time of the study were recorded. All samples were analyzed for CYP2D6*2 polymorphism using the polymerase chain reaction-restriction fragment length polymorphism method. The genotype distribution did not vary significantly among genders [NR (P = 0.723); R (P = 0.947)] and different age groups in NRs (P = 0.763) and Rs (P = 0.268). Clinically, statistically significant (P < 0.001) results were obtained in both the groups when compared with baseline in the NRS-sleep and GPE scores, whereas no association was found between NRS-sleep and GPE scores when compared with CYP2D6*2 genotype (P > 0.05). In addition, CYP2D6*2 genotype was not related to the adverse effects of analgesic therapy. The overall results suggested that CYP2D6*2 polymorphism plays no role in the PHN patients receiving tramadol treatment. The CYP2D6*2 polymorphism may not be a predictor of treatment outcome of patients with respect to PHN-receiving tramadol.

Estimation of the minimum effective dose of tramadol for postoperative analgesia in infants using the continual reassessment method

Tramadol is a potent analgesic. However, the analgesia efficacy of tramadol, particularly its minimum effective dose (MED), is not clear. The aim of this study is to find MED of tramadol for postoperative analgesia in infants. The continual reassessment method (CRM) was performed to find MED. Infants undergoing surgeries were included in the 3 phases of this series. In each phase, 24 participants were allocated a different tramadol dose. Pain intensity was measured by face, legs, activity, cry, consolability (FLACC) measurement at 3-hour intervals. Tramadol was considered ineffective if the FLACC score was higher than 4 in 10 at anytime. In phase 1, seven dose levels were used within the range 0.1-0.4 mg·kg(-1)·h(-1). Phase 1 was insufficient to identify the MED, and we increased the dose to 0.4-0.8 mg·kg(-1)·h(-1) in phase 2. Phase 2 was insufficient to identify the MED. In phase 3, local anesthetic wound infiltration was introduced, and the tramadol dose levels tested were the same as in phase 1. The successful analgesia probability of tramadol 0.4 mg·kg(-1)·h(-1) was 82.1% (95% CI, 0.742-0.925) in phase 1. In phase 2, it was 84.7% (95% CI, 0.789-0.991) with the dose 0.8 mg·kg(-1)·h(-1). Phase 1 and phase 2 were insufficient to identify the MED. In phase 3, the successful analgesia probability for dose 0.35 mg·kg(-1)·h(-1) was 96.7% (95% CI, 0.853-0.997).We have demonstrated that tramadol provides insufficient analgesia for surgeries considered to cause moderate-to-severe postoperative pain in infants if used as the sole analgesic, and that local anesthetic wound infiltration enhances the efficacy of tramadol.

CYP2D6*4 polymorphism, tramadol treatment and its clinical impact in patients with postherpetic neuralgia

Aim: The aim of this study was to investigate the associations between the CYP2D6*4 polymorphism, interindividual differences in CYP2D6 activity and adverse drug effects in postherpetic neuralgia (PHN) patients receiving tramadol. Patients & methods: The study comprised 158 patients (including 78 nonresponders and 80 responders) with PHN who were undergoing analgesic treatment at the Pain Clinic in the Out Patient Department of the University College of Medical Sciences, Guru Teg Bahadur Hospital (New Delhi, India). The numerical rating scale scores were measured at the resting and movement stages; Neuropathic Pain Symptom Inventory scores were evaluated by the treating physician. WHO-brief questionnaire scores for quality of life and adverse drug effects during the time of study were recorded. All samples were analyzed for the CYP2D6*4 polymorphism using the PCR-restriction fragmentation length polymorphism method. Results: The genotype distribution did not vary significantly among different age groups in nonresponders and responders. The CYP2D6*4 polymorphism was significantly associated with lower Neuropathic Pain Symptom Inventory (burning, squeezing stabbing and pressure) scores. The quality-of-life (sociological, psychological and environmental domains) scores correlated with CYP2D6*4 and showed significant results (p < 0.05) using a generalized linear model. No association was found between the physiological domain compared with the CYP2D6*4 allele (p > 0.05). In addition, the homozygous mutated CYP2D6*4 allele was not related to adverse effects of analgesic therapy. Conclusion: The CYP2D6*4 polymorphism may not be a predictor for treatment outcome of patients with PHN receiving tramadol. However, further investigation is required to confirm these findings in a larger sample size.

Enzyme-based amperometric platform to determine the polymorphic response in drug metabolism by cytochromes P450

"Personalized medicine" is a new concept in health care, one aspect of which defines the specificity and dosage of drugs according to effectiveness and safety for each patient. Dosage strongly depends from the rate of metabolism which is primarily regulated by the activity of cytochrome P450. In addition to the need for a genetic characterization of the patients, there is also the necessity to determine the drug-clearance properties of the polymorphic P450 enzyme. To address this issue, human P450 2D6 and 2C9 were engineered and covalently linked to an electrode surface allowing fast, accurate, and reliable measurements of the kinetic parameters of these phase-1 drug metabolizing polymorphic enzymes. In particular, the catalytic activity of P450 2C9 on the electrode surface was found to be improved when expressed from a gene-fusion with flavodoxin from Desulfovibrio vulgaris (2C9/FLD). The results are validated using marker drugs for these enzymes, bufuralol for 2D6, and warfarin for 2C9/FLD. The platform is able to measure the same small differences in K(M), and it allows a fast and reproducible mean to generated the product identified by HPLC from which the k(cat) is calculated.

Tramadol use in zoologic medicine

Numerous analgesics are available for use in animals, but only a few have been used or studied in zoologic species. Tramadol is a relatively new analgesic that is available in an inexpensive, oral form, and is not controlled. Studies examining the effect of tramadol in zoologic species suggest that significant differences exist in pharmacokinetics parameters as well as analgesic dynamics. This article reviews the current literature on the use of tramadol in humans, domestic animals, and zoologic species.

Tolerance and withdrawal from prolonged opioid use in critically ill children

OBJECTIVE

After prolonged opioid exposure, children develop opioid-induced hyperalgesia, tolerance, and withdrawal. Strategies for prevention and management should be based on the mechanisms of opioid tolerance and withdrawal.

PATIENTS AND METHODS

Relevant manuscripts published in the English language were searched in Medline by using search terms "opioid," "opiate," "sedation," "analgesia," "child," "infant-newborn," "tolerance," "dependency," "withdrawal," "analgesic," "receptor," and "individual opioid drugs." Clinical and preclinical studies were reviewed for data synthesis.

RESULTS

Mechanisms of opioid-induced hyperalgesia and tolerance suggest important drug- and patient-related risk factors that lead to tolerance and withdrawal. Opioid tolerance occurs earlier in the younger age groups, develops commonly during critical illness, and results more frequently from prolonged intravenous infusions of short-acting opioids. Treatment options include slowly tapering opioid doses, switching to longer-acting opioids, or specifically treating the symptoms of opioid withdrawal. Novel therapies may also include blocking the mechanisms of opioid tolerance, which would enhance the safety and effectiveness of opioid analgesia.

CONCLUSIONS

Opioid tolerance and withdrawal occur frequently in critically ill children. Novel insights into opioid receptor physiology and cellular biochemical changes will inform scientific approaches for the use of opioid analgesia and the prevention of opioid tolerance and withdrawal.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.