Acute liver injury induced by drug interaction between dacomitinib and metoprolol due to the inhibition of CYP2D6 by dacomitinib.

INTRODUCTION: In recent years, oral antineoplastic agents are commonly used in antitumor therapy. The interaction between drugs may affect the efficacy of drugs or lead to adverse reactions. We describe the case of a patient who presented acute liver injury, possibly induced by the concomitant use of metoprolol and dacomitinib. CASE REPORT: A 62-year-old male patient with non-small cell lung cancer was admitted for anti-cancer treatment. He regularly took metoprolol tartrate 12.5 mg, 2/day for hypertension. He was treated with dacomitinib according to EGFR Exon21 L858R positive. After 3 days of dacomitinib, the patient's alanine aminotransferase (ALT) and glutathione aminotransferase (AST) increased, and the heart rate and systolic blood pressure of the patient decreased significantly. The patient was diagnosed with acute liver injury. MANAGEMENT AND OUTCOMES: Dacomitinib was discontinued and glutathione, magnesium isoglycyrrhizinate were given to treat acute liver injury. Two days after discontinued dacomitinib, the patient's heart rate increased, but the ALT and AST of the patient elevated again. Metoprolol tartrate was subsequently discontinued and the ALT and AST gradually decreased and the patient discharged from the hospital eight days later with his liver function improved. DISCUSSION: To our knowledge, this is the first case in the literature of acute liver injury possibly induced by the interaction between metoprolol and dacomitinib. The interaction most likely arose because dacomitinib is a CYP2D6 strong inhibitor and could therefore impair the metabolism of metoprolol (a CYP2D6 substrate) and increase its serum concentration. Therefore, hepatic function should be carefully monitored in patients treated with dacomitinib and metoprolol and other inhibitors or inducers of CYP2D6.

Co-prescription of metoprolol and CYP2D6-inhibiting antidepressants before and after implementation of an optimized drug interaction database in Norway.

PURPOSE: To compare the co-prescription of metoprolol and potent CYP2D6-inhibiting antidepressants before and during a 10-year period after implementation of an optimized drug interaction database into clinical decision support systems in Norway. METHODS: The study was a retrospective, cross-sequential nationwide analysis of drug-dispensing data retrieved from the Norwegian Prescription Database over a 1-year period before (2007) and two 1-year periods after (2012 and 2017) implementation of a drug interaction database providing recommendations on non-interacting alternative medications. Primary outcome was changes in co-prescription rates of metoprolol and the potent CYP2D6-inhibiting antidepressants fluoxetine, paroxetine, or bupropion relative to alternative antidepressants with no or limited CYP2D6 inhibitory potential. To control for potential secular trend bias, a comparison group consisting of atenolol/bisoprolol users was included. RESULTS: The co-prescription rate of metoprolol with potent CYP2D6 inhibitors declined following implementation of the optimized database, by 21% (P < 0.001) after 5 years and by 40% (P < 0.001) after 10 years. Compared with atenolol/bisoprolol users, patients treated with metoprolol had significantly reduced likelihood of being prescribed a CYP2D6-inhibiting antidepressant in the two post-implementation periods (OR 0.61 (95% CI 0.54-0.69) and OR 0.45 (95% CI 0.40-0.51), respectively, versus OR 0.84 (95% CI 0.74-0.94) prior to implementation). Small and mostly insignificant differences in average daily metoprolol dosage were found between patients treated with the various antidepressants. CONCLUSION: The present study suggests that implementation of a drug interaction database providing recommendations on non-interacting drug alternatives contributes to reduced co-prescribing of drug combinations associated with potentially serious adverse effects.

CYP2D6 as a treatment decision aid for ER-positive non-metastatic breast cancer patients: a systematic review with accompanying clinical practice guidelines.

PURPOSE: Tamoxifen is one of the principal treatments for estrogen receptor (ER)-positive breast cancer. Unfortunately, between 30 and 50% of patients receiving this hormonal therapy relapse. Since CYP2D6 genetic variants have been reported to play an important role in survival outcomes after treatment with tamoxifen, this study sought to summarize and critically appraise the available scientific evidence on this topic. METHODS: A systematic literature review was conducted to identify studies investigating associations between CYP2D6 genetic variation and survival outcomes after tamoxifen treatment. Critical appraisal of the retrieved scientific evidence was performed, and recommendations were developed for CYP2D6 genetic testing in the context of tamoxifen therapy. RESULTS: Although conflicting literature exists, the majority of the current evidence points toward CYP2D6 genetic variation affecting survival outcomes after tamoxifen treatment. Of note, review of the CYP2D6 genotyping assays used in each of the studies revealed the importance of comprehensive genotyping strategies to accurately predict CYP2D6 metabolizer phenotypes. CONCLUSIONS AND RECOMMENDATIONS: Critical appraisal of the literature provided evidence for the value of comprehensive CYP2D6 genotyping panels in guiding treatment decisions for non-metastatic ER-positive breast cancer patients. Based on this information, it is recommended that alternatives to standard tamoxifen treatments may be considered in CYP2D6 poor or intermediate metabolizers.

Rolapitant Is a Reversible Inhibitor of CYP2D6.

Rolapitant [(Varubi), 5S,8S)-8-[[(1R)-1-[3,5 bis(trifluoromethyl phenyl]ethoxy]methyl]-8-phenyl-1,7-diazaspiro[4.5]decan-2-one] is a high-affinity NK1 receptor antagonist that was approved in September 2015 as a treatment for nausea and vomiting caused by chemotherapy. In vivo rolapitant moderately inhibits CYP2D6 for at least 7 days after one 180 mg dose. Due to the long inhibition time, we investigated rolapitant as a possible mechanism-based inactivator of CYP2D6. Rolapitant docked in the active site of CYP2D6 and displayed type I binding to CYP2D6 with a K s value of 1.2 ± 0.4 µM. However, in NADPH-, time-, and concentration-dependent assays of CYP2D6 activity, no evidence for mechanism-based inactivation and no metabolites of rolapitant were observed. Stopped-flow binding studies yielded a kon /koff (K d) value of 6.2 µM. The IC50 value for rolapitant inhibition of CYP2D6 activity was 24 µM, suggesting that inhibition is not due to tight binding of rolapitant to CYP2D6. By Lineweaver-Burk analysis, rolapitant behaved as a mixed, reversible inhibitor. The K i values of 20 and 34 µM were determined by Dixon analysis, with bufuralol and dextromethorphan as reporter substrates, respectively, and drug-drug interaction modeling did not predict the reported in vivo inhibition. The interaction of rolapitant with CYP2D6 was also examined in 1 microsecond molecular dynamics simulations. Rolapitant adopted multiple low-energy binding conformations near the active site, but at distances not consistent with metabolism. Given these findings, we do not see evidence that rolapitant is a mechanism-based inactivator. Moreover, the reversible inhibition of CYP2D6 by rolapitant may not fully account for the moderate inhibition described in vivo.

Long-term safety and efficacy of deutetrabenazine for the treatment of tardive dyskinesia.

OBJECTIVE: To evaluate the long-term safety and efficacy of deutetrabenazine in patients with tardive dyskinesia (TD). METHOD: Patients with TD who completed the 12 week, phase 3, placebo-controlled trials were eligible to enter this open-label, single-arm study. The open-label study consisted of a 6 week dose-escalation phase and a long-term maintenance phase (clinic visits at Weeks 4, 6 and 15, and every 13 weeks until Week 106). Patients began deutetrabenazine at 12 mg/day, titrating up to a dose that was tolerable and provided adequate dyskinesia control, based on investigator judgement, with a maximum allowed dose of 48 mg/day (36 mg/day for patients taking strong cytochrome P450 2D6 (CYP2D6) inhibitors). Safety measures included incidence of adverse events (AEs) and scales used to monitor parkinsonism, akathisia/restlessness, anxiety, depression, suicidality and somnolence/sedation. Efficacy endpoints included the change in Abnormal Involuntary Movement Scale (AIMS) score (items 1 to 7) from baseline and the proportion of patients rated as 'Much Improved' or 'Very Much Improved' on the Clinical Global Impression of Change. RESULTS: A total of 343 patients enrolled in the extension study, and there were 331 patient-years of exposure in this analysis. The exposure-adjusted incidence rates of AEs with long-term treatment were comparable to or lower than those observed in the phase 3 trials. The mean (SE) change in AIMS score was -4.9 (0.4) at Week 54 (n = 146), - 6.3 (0.7) at Week 80 (n = 66) and -5.1 (2.0) at Week 106 (n = 8). CONCLUSIONS: Overall, long-term treatment with deutetrabenazine was efficacious, safe, and well tolerated in patients with TD. TRIAL REGISTRATION NUMBER: NCT02198794.

Neuron and neuroblast numbers and cytogenesis in the dentate gyrus of aged APPswe/PS1dE9 transgenic mice: Effect of long-term treatment with paroxetine.

Altered neurogenesis may influence hippocampal functions such as learning and memory in Alzheimer's disease. Selective serotonin reuptake inhibitors enhance neurogenesis and have been reported to reduce cerebral amyloidosis in both humans and transgenic mice. We have used stereology to assess the longitudinal changes in the number of doublecortin-expressing neuroblasts and number of granular neurons in the dentate gyrus of APPswe/PS1dE9 transgenic mice. Furthermore, we investigated the effect of long-term paroxetine treatment on the number of neuroblasts and granular neurons, hippocampal amyloidosis, and spontaneous alternation behaviour, a measure of spatial working memory, in transgenic mice. We observed no difference in granular neurons between transgenic and wild type mice up till 18months of age, and no differences with age in wild type mice. The number of neuroblasts and the performance in the spontaneous alternation task was reduced in aged transgenic mice. Paroxetine treatment from 9 to 18months of age reduced hippocampal amyloidosis without affecting the number of neuroblasts or granular neurons. These findings suggest that the amyloidosis affects the differentiation of neuroblasts and spatial working memory, independent of changes in total granular neurons. Furthermore, while long-term paroxetine treatment may be able to reduce hippocampal amyloidosis, it appears to have no effect on total number of granular neurons or spatial working memory.

Metoprolol-pridopidine drug-drug interaction and food effect assessments of pridopidine, a new drug for treatment of Huntington's disease.

AIMS: Pridopidine is an oral drug in clinical development for treatment of patients with Huntington's disease. This study examined the interactions of pridopidine with in vitro cytochrome P450 activity and characterized the effects of pridopidine on CYP2D6 activity in healthy volunteers using metoprolol as a probe substrate. The effect of food on pridopidine exposure was assessed. METHODS: The ability of pridopidine to inhibit and/or induce in vitro activity of drug metabolizing enzymes was examined in human liver microsomes and fresh hepatocytes. CYP2D6 inhibition potency and reversibility was assessed using dextromethorphan. For the clinical assessment, 22 healthy subjects were given metoprolol 100 mg alone and concomitantly with steady-state pridopidine 45 mg twice daily. Food effect on a single 90 mg dose of pridopidine was evaluated in a crossover manner. Safety assessments and pharmacokinetic sampling occurred throughout the study. RESULTS: Pridopidine was found to be a metabolism dependent inhibitor of CYP2D6, the main enzyme catalysing its own metabolism. Flavin-containing monooxygenase heat inactivation of liver microsomes did not affect pridopidine metabolism-dependent inhibition of CYP2D6 and its inhibition of CYP2D6 was not reversible with addition of FeCN3 . Exposure to metoprolol was markedly increased when coadministered with pridopidine; the ratio of the geometric means (90% confidence interval) for maximum observed plasma concentration, and area under the plasma concentration-time curve from time 0 to the time of the last quantifiable concentration and extrapolated to infinity were 3.5 (2.9, 4.22), 6.64 (5.27, 8.38) and 6.55 (5.18, 8.28), respectively. Systemic exposure to pridopidine was unaffected by food conditions. CONCLUSIONS: As pridopidine is a metabolism-dependent inhibitor of CYP2D6, systemic levels of drugs metabolized by CYP2D6 may increase with chronic coadministration of pridopidine. Pridopidine can be administered without regard to food.

Delirium associated with concomitant use of duloxetine and bupropion in an elderly patient.

Delirium is common in daily practice. Drug-induced delirium constitutes approximately one-third of all cases of delirium. In cases characterized by the limited efficacy of a single antidepressant, a combination of two antidepressants is required, which may induce a complex drug-drug interaction. We reviewed a case of duloxetine- and bupropion-related delirium in an elderly male patient in our clinical practice. The patient was diagnosed with major depressive disorder and was treated with duloxetine. However, he developed delirium 10 days after bupropion was added to his treatment regimen. Three days after the cessation of bupropion, his delirious condition gradually improved. Duloxetine and bupropion are both cytochrome P450 2D6 inhibitors that may result in a higher level of hydroxybupropion. An increased level of hydroxybupropion may cause the elevation of dopamine and a risk of subsequent delirium. We should be aware of the risk of delirium induced by drug-drug interactions.

Topical Treatment of Leishmania tropica Infection Using (-)-α-Bisabolol Ointment in a Hamster Model: Effectiveness and Safety Assessment.

There is currently no reliable treatment for the management of cutaneous leishmaniasis, and intralesional antimonial injections remain the main treatment. The present work aims at evaluating the antileishmanial effectiveness and safety of (-)-α-bisabolol (1) in a novel topical formulation on a cutaneous leishmaniasis model involving Leishmania tropica-infected Syrian hamsters. The topical treatment with 1 reduced lesion thickness to 56% at 2.5%, showing a higher efficacy than the reference control, meglumine antimoniate. Other regimens (ointment at 1% and 5% and oral treatment at 200 mg/kg) reduced the footpad thickness as well. The skin parasite load decreased after the experiment in all treatment groups, particularly in those animals treated with the 2.5% formulation (83.2%). Treatment with (-)-α-bisabolol at different concentrations or through an oral route did not lead to the appearance of toxicity or side effects in healthy hamsters or infected animals. Therefore, topical (-)-α-bisabolol was more effective than meglumine antimoniate in this cutaneous leishmaniasis model without showing toxicity effects on the hamsters. These results are of great interest and might be used for the development of alternatives for the treatment of cutaneous leishmaniasis, either in monotherapy or in combination with other drugs whose skin permeability could be enhanced by this sesquiterpene.

Response to CYP2D6 substrate antidepressants is predicted by a CYP2D6 composite phenotype based on genotype and comedications with CYP2D6 inhibitors.

The cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of most antidepressants. Comedication with a potent CYP2D6 inhibitor can convert patients with extensive metabolizer (EM) or ultra-rapid metabolizer (UM) genotypes into poor metabolizer (PM) phenotypes. Since comedication is frequent in depressed patients treated with antidepressants, we investigated the effect of the CYP2D6 composite phenotype on antidepressant efficacy, taking into account both the CYP2D6 genotype and comedication with CYP2D6 inhibitors. 87 Caucasian in patients with a major depressive episode were prospectively treated with flexible doses of antidepressant monotherapy as well as comedications and genotyped for the major CYP2D6 alleles (CYP2D6*3 rs35742686, *4 rs3892097, *5 del, *6 rs5030655, and *2xN). They were classified for CYP2D6 composite phenotype and assessed for antidepressant response after 4 weeks. In terms of genotypes (g), 6 subjects were UMg, 6 PMg, and 75 EMg. Ten patients were coprescribed a CYP2D6 inhibitor, resulting in the following composite phenotypes (cp): 5 UMcp, 16 PMcp, and 66 EMcp. Whereas none of the CYP2D6 genotypes were significantly associated with antidepressant response, UMcp had a lower antidepressant response than PMcp or EMcp (respectively: 39.0 ± 17.9, 50.0 ± 26.0, and 61.6 ± 23.4, p = 0.02). Despite small sample size, this study suggests that a CYP2D6 composite phenotype, taking into account both genotype and comedications with CYP2D6 inhibitors, could predict CYP2D6 substrate antidepressants response. Thus, to optimize antidepressant response, CYP2D6 genotype could be performed and comedications with CYP2D6 inhibitors should be avoided, when prescribing CYP2D6 substrate antidepressants.

Melperone but not bisoprolol or metoprolol is a clinically relevant inhibitor of CYP2D6: evidence from a therapeutic drug monitoring survey.

Cytochrome P450 enzymes (CYP) can be inhibited or induced by drugs, resulting in clinically significant drug-drug interactions that can cause unanticipated adverse reactions or therapeutic failures. The objective of the study was to analyze the in vivo inhibitory potential of the beta-blockers bisoprolol and metoprolol as well as the low-potency antipsychotic melperone on CYP2D6. By utilizing a large therapeutic drug monitoring database of 2874 samples, data from patients who had been treated with venlafaxine (VEN) either without (control group) or with a concomitant medication with bisoprolol, metoprolol or melperone were evaluated retrospectively to study the CYP2D6-catalyzed O-demethylation to O-desmethylvenlafaxine (ODVEN). Dose-adjusted serum levels (C/D) of VEN and ODVEN as well as the metabolic ratios (ODVEN/VEN) were computed for the four groups and compared using Kruskal-Wallis test. In total, 381 patients could be included for analysis. No significant difference was found in the median C/D (VEN), C/D (ODVEN) or C/D of the active moiety (VEN + ODVEN) in either the metoprolol (N = 103) or bisoprolol group (N = 101), compared to the control group (N = 108). In contrast, a significantly higher median C/D (VEN) (0.79 ng/ml/mg, range 0.13-5.73 ng/ml/mg) (P < 0.01) was found in the melperone group (N = 69), compared to the control group (0.46 ng/ml/mg, range 0.02-7.39 ng/ml/mg). A significant decrease (P < 0.01) was solely found in the median metabolic ratios of ODVEN/VEN between the melperone group (0.90, range 0.14-15.15), compared to the control group (2.39, range 0.06-15.31). The results of this study provided evidence that melperone but not bisoprolol or metoprolol has a clinically relevant inhibitory potential on CYP2D6.

The Effect of Tamoxifen Dose Increment in Patients With Impaired CYP2D6 Activity.

BACKGROUND: The effect of tamoxifen dose elevation on endoxifen serum concentration was investigated in patients with reduced CYP2D6 activity resulting from genetic variation and/or CYP2D6 inhibitor use. Additionally, baseline differences in endoxifen concentrations between the different CYP2D6 phenotypes were studied. METHODS: Patients, treated with tamoxifen 20 mg once daily (QD) for at least 4 weeks, were classified as phenotypic extensive (EM), intermediate (IM), or poor (PM) metabolizer based on their genotype and comedication. In patients with an IM or PM phenotype, the tamoxifen dose was increased to 40 mg QD for 4 weeks. Tamoxifen, 4-OH-tamoxifen, N-desmethyltamoxifen, and endoxifen serum concentrations were measured at baseline and 4 weeks after the dose increment. Side effects of tamoxifen were assessed using the validated Functional Assessment of Cancer Therapy-Endocrine Symptom subscale (FACT-ESS-19). RESULTS: The median baseline endoxifen concentration differed between EMs (11.4 mcg/L: n = 19), IMs (8.3 mcg/L: n = 16), and PMs (4.0 mcg/L: n = 7), P = 0.040. Tamoxifen dose elevation significantly increased the median endoxifen concentrations in 12 IMs from 9.5 to 17.4 mcg/L (P < 0.001) and in 4 PMs from 3.8 to 7.8 mcg/L (P = 0.001), without influencing median FACT-ESS-19 scores. CONCLUSIONS: Raising the tamoxifen dose to 40 mg QD significantly increased endoxifen concentrations in IMs and PMs without increasing side effects. The tamoxifen dose increment in PMs was insufficient to reach endoxifen concentrations equal to those observed in EMs. Future studies will clarify the direct effect of endoxifen exposure on tamoxifen efficacy and may reveal a threshold endoxifen concentration that is critical for its efficacy.

Paroxetine markedly increases plasma concentrations of ophthalmic timolol; CYP2D6 inhibitors may increase the risk of cardiovascular adverse effects of 0.5% timolol eye drops.

Although ophthalmic timolol is generally well tolerated, a significant fraction of topically administered timolol can be systemically absorbed. We investigated the effect of the strong CYP2D6 inhibitor paroxetine on the pharmacokinetics of timolol after ophthalmic administration. In a four-phase crossover study, 12 healthy volunteers ingested either paroxetine (20 mg) or placebo daily for 3 days. In phases 1-2, timolol 0.1% gel, and in phases 3-4, timolol 0.5% drops were administered to both eyes. Paroxetine increased the plasma concentrations of timolol with both timolol formulations to a similar degree. The geometric mean ratio (95% confidence interval) of timolol peak concentration was 1.53-fold (1.23-1.91) with 0.1% timolol and 1.49-fold (0.94-2.36) with 0.5% timolol, and that of timolol area under the plasma concentration-time curve (AUC) from time 0 to 12 hours was 1.61-fold (1.26- to 2.06-fold) and 1.78-fold (1.21-2.62), respectively. During paroxetine administration, six subjects on 0.5% timolol drops, but none on 0.1% timolol gel, had plasma timolol concentrations exceeding 0.7 ng/ml, which can cause systemic adverse effects in patients at risk. There was a positive correlation between the AUC from time 0 to 13 hours of paroxetine and the placebo phase AUC from time 0 to infinity of timolol after timolol 0.5% drops (P < 0.05), and a nonsignificant trend after timolol 0.1% gel, consistent with the role of CYP2D6 in the metabolism of both agents. In the orthostatic test, heart rate immediately after upright standing was significantly lower (P < 0.05) during the paroxetine phase than during the placebo phase at 1 and 3 hours after 0.5% timolol dosing. In conclusion, paroxetine and other CYP2D6 inhibitors can have a clinically important interaction with ophthalmic timolol, particularly when patients are using 0.5% timolol formulations.

Bupropion Ameliorates Acetic Acid-Induced Colitis in Rat: the Involvement of the TLR4/NF-kB Signaling Pathway.

Inflammatory bowel disease composed of ulcerative colitis and Crohn's disease is a disorder that may involve entire gastrointestinal tract. Its pathogenesis is mainly an immune-mediated inflammation. Recently, it has been indicated that bupropion possesses anti-inflammatory properties; hence, the objective of this experiment is the investigation of the anti-inflammatory influence of bupropion on colonic lesions that emerged following the intrarectal administration of acetic acid. Thirty-six male Wistar rats were allocated randomly into six groups, including control, acetic acid, dexamethasone (2 mg/kg), and bupropion (40, 80, and 160 mg/kg). Colitis was induced by intrarectal administration of acetic acid in all study groups except control group, and animals were treated by oral administration of dexamethasone and bupropion. While macroscopic and microscopic lesions were observed after colitis induction, administration of dexamethasone and bupropion 160 mg/kg led to the remarkable improvement in lesions. In addition, the expression of TLR4 and NF-ĸB was decreased after colitis induction; however, treatment with dexamethasone (2 mg/kg) and bupropion (160 mg/kg) resulted in a significant decrease in their expression. Regarding biochemical factors, following colitis induction, TNF-α level and MPO activity were increased; nevertheless, dexamethasone (2 mg/kg) and bupropion (160 mg/kg) decreased the TNF-α and MPO activity. In conclusion, bupropion exerts anti-inflammatory influence through suppressing the TLR4 and NF-ĸB expression in the rat model of acute colitis.

Efficacy of Tramadol for Pain Management in Patients Receiving Strong Cytochrome P450 2D6 Inhibitors.

STUDY OBJECTIVE: Tramadol is metabolized by cytochrome P450 (CYP) 2D6 to form an active metabolite that exhibits its analgesic effect. Medications that inhibit this enzyme are used often in practice, yet the clinical impact of this interaction on the analgesic effects of tramadol has yet to be fully described. The objective was to determine whether a clinically relevant decrease in pain control is observed in patients taking scheduled tramadol concomitantly with a strong CYP2D6 inhibitor. DESIGN: Retrospective cohort study. SETTING: Large health care system. PATIENTS: One hundred fifty-two adult inpatients who received scheduled tramadol for at least 24 hours with (76 patients) or without (76 patients) a strong CYP2D6 inhibitor between January 1, 2012, and February 28, 2017, were included in the analysis. Patients hospitalized for opioid use disorder or those receiving substandard dosing of tramadol were excluded. MEASUREMENTS AND MAIN RESULTS: The primary outcome was mean breakthrough opiate consumption in the presence and absence of CYP2D6 inhibitors. Secondary outcomes included mean pain scores, length of hospital stay, tramadol discontinuation rates, and prespecified subgroup analyses based on patient sex, race, and specific CYP2D6 inhibitor administered. Patients receiving concurrent CYP2D6 inhibitors required significantly more breakthrough morphine milligram equivalents per day compared with patients receiving scheduled tramadol without CYP2D6 inhibitors (geometric mean ± SD 18.2 ± 6.3 vs 5.7 ± 6.7 mg morphine milligram equivalents, p<0.001). No significant differences existed between cohorts for mean pain score, length of hospital stay, or tramadol discontinuation rate. CONCLUSION: This study demonstrated a clinically relevant decrease in the efficacy of tramadol when used for pain control in patients receiving a strong CYP2D6 inhibitor. These results should encourage clinicians to review medication lists for this interaction and adjust regimens accordingly to ensure adequate pain control.

Pharmacogenomic-pharmacokinetic study of selective estrogen-receptor modulators with intra-patient dose escalation in breast cancer.

BACKGROUND: An association between CYP2D6 polymorphisms and tamoxifen (TAM) efficacy has not been confirmed, partly due to unreliable prediction of active metabolite exposure solely by CYP2D6 activity. The efficacy of TAM dose escalation appears limited in poor TAM metabolizers. Since the chlorine atom on the side chain of toremifene (TOR) prevents 4-hydroxylation by CYP2D6, its contribution to active conversion of TOR is minor. We examined the role of TOR and its dose escalation among poor TAM metabolizers. METHODS: The pharmacokinetics (PK) and pharmacogenomics (PGx) of TAM and TOR were studied. Correlation between PK and CYP2D6 inhibitor use, smoking status, and PGx were examined by regression analysis. For patients showing low endoxifen levels, an intra-patient dose escalation of TOR was conducted, and TOR was increased from 40 to 120 mg for ≥ 24 weeks with PK sampling. Total activity was calculated as the sum of the concentration of each active metabolite adjusted by their respective in vitro activities. RESULTS: Fifty and 11 of the 273 participating patients had endoxifen levels < 15 and < 7.5 ng/mL, respectively. The CYP2D6 genotype was the major determinant for TAM activity (p < 0.01). Smoking status (p = 0.07) and the CYP2C19 phenotype (p = 0.07), but not the CYP2D6 genotype (p = 0.61), showed marginally significant effects on TOR activity. TOR activity increased significantly with dose escalation, even among poor TAM metabolizers, and was maintained for ≥ 24 weeks. CONCLUSION: TOR might be a valid alternative to TAM in patients predicted to be poor TAM metabolizers.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and Tamoxifen Therapy.

Tamoxifen is biotransformed by CYP2D6 to 4-hydroxytamoxifen and 4-hydroxy N-desmethyl tamoxifen (endoxifen), both with greater antiestrogenic potency than the parent drug. Patients with certain CYP2D6 genetic polymorphisms and patients who receive strong CYP2D6 inhibitors exhibit lower endoxifen concentrations and a higher risk of disease recurrence in some studies of tamoxifen adjuvant therapy of early breast cancer. We summarize evidence from the literature and provide therapeutic recommendations for tamoxifen based on CYP2D6 genotype.

Predictors of medication adherence and smoking cessation among smokers under community corrections supervision.

INTRODUCTION: Individuals in the U.S. criminal justice system now represent over 12% of all current U.S. smokers. With smoking banned in most U.S. jails and prisons, the cessation focus for this population has shifted to individuals who are under community correction supervision (e.g., probation, parole). The aim of this study was to examine predictors of successful smoking cessation among criminal justice individuals supervised in the community. METHODS: Five hundred participants under community corrections supervision were randomized to receive either four sessions of smoking cessation counseling or no counseling in conjunction with 12weeks of bupropion treatment plus brief physician advice to quit. Logistic regression analyses examined associations of smoking variables with medication adherence and successful abstinence. Mediation analysis evaluated the indirect effects of medication adherence on smoking abstinence. RESULTS: The strongest associate of medication adherence was previous use of bupropion, while the strongest associate of smoking abstinence was medication adherence. Mediation analysis indicated that previous use of bupropion indirectly increased cessation rates through the pathway of increased medication adherence. CONCLUSIONS: These results highlight the importance of medication adherence for smoking cessation among community corrections smokers. Providing exposure to medication may be a promising intervention to increase medication adherence and subsequent cessation rates in this population.