CYP2D6 inhibition by fluoxetine, paroxetine, sertraline, and venlafaxine in a crossover study: intraindividual variability and plasma concentration correlations

CYP2D6 phenotypes and opioid metabolism: the path to personalized analgesia

INTRODUCTION

Opioids play a fundamental role in chronic pain, especially considering when 1 of 5 Europeans adults, even more in older females, suffer from it. However, half of them do not reach an adequate pain relief. Could pharmacogenomics help to choose the most appropriate analgesic drug?

AREAS COVERED

The objective of the present narrative review was to assess the influence of cytochrome P450 2D6 (CYP2D6) phenotypes on pain relief, analgesic tolerability, and potential opioid misuse. Until December 2021, a literature search was conducted through the MEDLINE, PubMed database, including papers from the last 10 years. CYP2D6 plays a major role in metabolism that directly impacts on opioid (tramadol, codeine, or oxycodone) concentration with differences between sexes, with a female trend toward poorer pain control. In fact, CYP2D6 gene variants are the most actionable to be translated into clinical practice according to regulatory drug agencies and international guidelines.

EXPERT OPINION

CYP2D6 genotype can influence opioids' pharmacokinetics, effectiveness, side effects, and average opioid dose. This knowledge needs to be incorporated in pain management. Environmental factors, psychological together with genetic factors, under a sex perspective, must be considered when you are selecting the most personalized pain therapy for your patients.

The effect of potent CYP2D6 inhibition on the pharmacokinetics and safety of deutetrabenazine in healthy volunteers

Purpose

Deutetrabenazine is a deuterated form of tetrabenazine with a confirmed lower rate of CYP2D6 metabolism of the active metabolites, α- and β-HTBZ. In this study, we assessed the effect of paroxetine, a potent CYP2D6 inhibitor, on the pharmacokinetics and safety of deutetrabenazine and its metabolites.

Methods

In this open-label sequential drug-drug-interaction study, 24 healthy adults who were CYP2D6 extensive or intermediate metabolizers received a single deutetrabenazine 22.5-mg oral dose on days 1 and 11 and a single paroxetine 20-mg oral daily dose on days 4–12. Pharmacokinetics of deutetrabenazine and its metabolites were assessed on days 1–4 and 11–14. Paroxetine trough concentrations were obtained pre-dose on days 9–13. Safety examinations occurred throughout the study.

Results

Paroxetine administered under steady-state conditions, increased exposure of the deuterated active metabolites, α-HTBZ (1.2-fold C_max and 1.8-fold AUC_0–∞) and β-HTBZ (2.1-fold C_max and 5.6-fold AUC_0–∞), and correspondingly, 1.6-fold C_max and threefold AUC_0–∞ for total (α + β)-HTBZ. Sixteen subjects reported 45 adverse events and most were mild. Headache was the most common AE reported 8 times by 7 subjects (5 following paroxetine alone; 2 following deutetrabenazine + paroxetine).

Conclusions

Paroxetine-induced increases in exposure to the active deutetrabenazine metabolites were less than those previously reported for tetrabenazine, a finding expected to reduce the burden of drug interaction. In addition, single doses of 22.5 mg deutetrabenazine, when given alone or in the presence of steady-state paroxetine (20 mg daily), were safe.

Supplementary information

The online version contains supplementary material available at 10.1007/s00228-021-03202-0.

Toward predicting CYP2D6-mediated variable drug response from CYP2D6 gene sequencing data

Pharmacogenomics is a key component of personalized medicine that promises safer and more effective drug treatment by individualizing drug choice and dose based on genetic profiles. In clinical practice, genetic biomarkers are used to categorize patients into *-alleles to predict CYP450 enzyme activity and adjust drug dosages accordingly. However, this approach leaves a large part of variability in drug response unexplained. Here, we present a proof-of-concept approach that uses continuous-scale (instead of categorical) assignments to predict enzyme activity. We used full CYP2D6 gene sequences obtained with long-read amplicon-based sequencing and cytochrome P450 (CYP) 2D6-mediated tamoxifen metabolism data from a prospective study of 561 patients with breast cancer to train a neural network. The model explained 79% of interindividual variability in CYP2D6 activity compared to 54% with the conventional *-allele approach, assigned enzyme activities to known alleles with previously reported effects, and predicted the activity of previously uncharacterized combinations of variants. The results were replicated in an independent cohort of tamoxifen-treated patients (model R ² adjusted = 0.66 versus *-allele R ² adjusted = 0.35) and a cohort of patients treated with the CYP2D6 substrate venlafaxine (model R ² adjusted = 0.64 versus *-allele R ² adjusted = 0.55). Human embryonic kidney cells were used to confirm the effect of five genetic variants on metabolism of the CYP2D6 substrate bufuralol in vitro. These results demonstrate the advantage of a continuous scale and a completely phased genotype for prediction of CYP2D6 enzyme activity and could potentially enable more accurate prediction of individual drug response.

Genetic influence of CYP2D6 on pharmacokinetics and acute subjective effects of LSD in a pooled analysis

Lysergic acid diethylamide (LSD) is a classic psychedelic substance that is used recreationally and investigated in psychiatric research. There are no pharmacogenetic studies on LSD. In vitro metabolic studies indicate that several cytochrome P450 (CYP) isoforms (e.g., CYP2D6, CYP1A2, and CYP2C9) are involved in LSD metabolism, but in vivo data are scarce. The present study examined the influence of genetic polymorphisms of CYP genes on the pharmacokinetics and acute effects of LSD in healthy subjects. We identified common genetic variants of CYPs (CYP2D6, CYP1A2, CYP2C9, CYP2C19, and CYP2B6) in 81 healthy subjects who were pooled from four randomized, placebo-controlled, double-blind Phase 1 studies. We found that genetically determined CYP2D6 functionality significantly influenced the pharmacokinetics of LSD. Individuals with no functional CYP2D6 (i.e., poor metabolizers) had longer LSD half-lives and approximately 75% higher parent drug and main metabolite 2-oxo-3-hydroxy LSD area-under-the-curve blood plasma concentrations compared with carriers of functional CYP2D6. Non-functional CYP2D6 metabolizers also exhibited greater alterations of mind and longer subjective effect durations in response to LSD compared with functional CYP2D6 metabolizers. No effect on the pharmacokinetics or acute effects of LSD were observed with other CYPs. These findings indicate that genetic polymorphisms of CYP2D6 significantly influence the pharmacokinetic and subjective effects of LSD. Given the potential therapeutic use of psychedelics, including LSD, the role of pharmacogenetic tests prior to LSD-assisted psychotherapy needs to be further investigated.

Impact of study design and statistical model in pharmacogenetic studies with gene-treatment interaction

Gene-treatment interactions, just like drug-drug interactions, can have dramatic effects on a patient response and therefore influence the clinician decision at the patient's bedside. Crossover designs, although they are known to decrease the number of subjects in drug-interaction studies, are seldom used in pharmacogenetic studies. We propose to evaluate, via realistic clinical trial simulations, to what extent crossover designs can help quantifying the gene-treatment interaction effect. We explored different scenarios of crossover and parallel design studies comparing two symptom-modifying treatments in a chronic and stable disease accounting for the impact of a one gene and one gene-treatment interaction. We varied the number of subjects, the between and within subject variabilities, the gene polymorphism frequency and the effect sizes of the treatment, gene, and gene-treatment interaction. Each simulated dataset was analyzed using three models: (i) estimating only the treatment effect, (ii) estimating the treatment and the gene effects, and (iii) estimating the treatment, the gene, and the gene-treatment interaction effects. We showed how ignoring the gene-treatment interaction results in the wrong treatment effect estimates. We also highlighted how crossover studies are more powerful to detect a treatment effect in the presence of a gene-treatment interaction and more often lead to correct treatment attribution.

Impact of Paroxetine, a Strong CYP2D6 Inhibitor, on SPN-812 (Viloxazine Extended-Release) Pharmacokinetics in Healthy Adults

SPN‐812 (viloxazine extended‐release) is a novel nonstimulant recently approved as a treatment for attention‐deficit/hyperactivity disorder in children and adolescents. Given that SPN‐812 is metabolized by CYP2D6 and may be coadministered with CYP2D6 inhibitors, this trial investigated the pharmacokinetics and safety of SPN‐812 coadministered with the potent CYP2D6 inhibitor paroxetine. In this single‐sequence, 3‐treatment period study in healthy volunteers, subjects received a single oral dose of 700 mg SPN‐812 alone (period 1), 20 mg daily paroxetine (10 days, period 2), followed by concurrent administration of SPN‐812 and paroxetine (period 3). Blood samples were collected for 72 hours post‐SPN‐812 dosing and analyzed for viloxazine and its primary metabolite, 5‐HVLX‐gluc. Twenty‐two healthy adults were enrolled; all completed the trial. The potential for drug interaction between SPN‐812 and paroxetine was assessed using analysis of variance on the log‐transformed pharmacokinetic parameters C_max, AUC_0‐t, and AUC_inf. The least‐squares geometric mean ratios for viloxazine were (reported as the ratio of combination/SPN‐812 alone) C_max, 116.04%; 90%CI, 109.49%‐122.99%; AUC_0‐t, 134.65%; 90%CI, 127.65‐142.03; and AUC_inf, 134.80%; 90%CI, 127.94%‐142.03%. CYP2D6 inhibition resulted in a modest change (<35%) on viloxazine AUCs with no change in C_max. All adverse events were mild in severity.

Assessing the Mechanism of Fluoxetine-Mediated CYP2D6 Inhibition

Fluoxetine is still one of the most widely used antidepressants in the world. The drug is extensively metabolized by several cytochrome P450 (CYP450) enzymes and subjected to a myriad of CYP450-mediated drug interactions. In a multidrug regimen, preemptive mitigation of drug-drug interactions requires knowledge of fluoxetine actions on these CYP450 enzymes. The major metabolic pathway of fluoxetine leading to the formation of its active metabolite, norfluoxetine, is mediated by CYP2D6. Fluoxetine and norfluoxetine are strong affinity substrates of CYP2D6 and can inhibit, potentially through various mechanisms, the metabolism of other sensitive CYP2D6 substrates. Remarkably, fluoxetine-mediated CYP2D6 inhibition subsides long after fluoxetine first passes through the liver and even remains long after the discontinuation of the drug. Herein, we review pharmacokinetic and pharmacogenetic information to help us understand the mechanisms underlying the prolonged inhibition of CYP2D6 following fluoxetine administration. We propose that long-term inhibition of CYP2D6 is likely a result of competitive inhibition. This is due to strong affinity binding of fluoxetine and norfluoxetine to the enzyme and unbound fluoxetine and norfluoxetine levels circulating in the blood for a long period of time because of their long elimination half-life. Additionally, we describe that fluoxetine is a CYP2C9 substrate and a mechanism-based inhibitor of CYP2C19.

Influence of combinations of drugs that act on the CYP2D6 metabolic pathway in the treatment of major depressive disorder: A population-based study

Objective

To describe the frequency of drug combinations (substrate-substrate or substrate-inhibitor) with the potential to interfere with the CYP2D6 metabolic pathway in patients receiving antidepressant medication for major depressive disorder.

Methods

We carried out an observational study using outpatient medical records. We included adult subjects who initiated antidepressant medication during 2008–2010. Patients were assigned to three study groups: no combination, substrate-substrate, and substrate-inhibitor. Follow-up period was 12 months. Main measures: demographics, comorbidity and medication persistence. Statistical analysis included a logistic regression model, P < 0.05.

Results

Five thousand six hundred and thirty patients were recruited (61.9 years, 76.9% female), 24.4% (CI: 23.8 – 26.0%) received some kind of drug combination (substrate-substrate: 15.4%, substrate-inhibitor: 9.0%). Variables significantly associated with drugs combinations that may act on the CYP2D6 metabolic pathway were: dementia (OR = 4.2), neuropathy (OR = 4.2) and stroke (OR = 1.9), P < 0.001. Medication persistence at 12 months was longer in patients with no combination (55.3%) than in patients receiving substrate-substrate (50.5%) or substrate-inhibitor (45.0%) combinations, P < 0.001.

Conclusions

Twenty-five percent of major depressive disorder patients received a combination of drugs with the potential to interfere with CYP2D6 metabolic pathway. These combinations increased with comorbidity and resulted in shorter medication persistence of antidepressant treatment.

Cytochrome P450 (CYP450) Interactions Involving Atypical Antipsychotics are Common in Community-Dwelling Older Adults Treated for Behavioral and Psychological Symptoms of Dementia

Treatment of behavioral and psychological symptoms of dementia (BPSD) and comorbidities often necessitates the concomitant use of antipsychotics and non-antipsychotic drugs, thereby potentiating the risk for drug–drug interactions (DDIs). The primary objective of our study was to identify potentially clinically relevant cytochrome P450 (CYP)-mediated DDIs involving antipsychotics among participants enrolled in the Program of All-Inclusive Care for the Elderly (PACE) with BPSD. Additionally, we wanted to determine the prevalence of antipsychotic use in this population. The study included 10,001 PACE participants. The practice setting used a proprietary clinical decision support system (CDSS) to analyze simultaneous multidrug interactions. A retrospective analysis of pharmacy claims data was conducted to identify DDIs involving antipsychotics prescribed for BPSD, using snapshots of medication profiles paired with the CDSS. Of the participants who met inclusion criteria, 1190 (11.9%) were prescribed an antipsychotic; of those, 1071 (90.0%) were prescribed an atypical antipsychotic. Aripiprazole commonly caused (being a perpetrator drug 94.6% of the time) potential DDIs with antidepressants (e.g., duloxetine, venlafaxine, mirtazapine), opioids (e.g., hydrocodone, oxycodone, tramadol) and metoprolol via the CYP2D6 isoform. Risperidone commonly caused (85.7%) potential DDIs with donepezil, lamotrigine and trazodone via the CYP3A4 isoform. Quetiapine exclusively suffered (100%) from potential DDIs with amlodipine, buspirone, omeprazole or topiramate via the CYP3A4 isoform. Antipsychotics are commonly prescribed to PACE participants for BPSD treatment and they may interact with other drugs used to treat comorbidities. A thorough review of concomitant medications will help mitigate the likelihood of potentially dangerous CYP-mediated DDIs involving antipsychotics.

Interactive Effects of Sertraline and Diphenhydramine on Biochemical and Behavioral Responses in Crucian Carp (Carassius auratus)

The ecotoxicity of psychiatric pharmaceuticals to aquatic organisms is being increasingly recognized. However, current ecological studies focus on the effects of individual psychiatric pharmaceuticals, with little attention being given to their combined effects. In this study, the interactive effects of two psychiatric pharmaceuticals, sertraline (SER) and diphenhydramine (DPH), on bioconcentration and biochemical and behavioral responses were investigated in crucian carp (Carassius auratus) after seven days of exposure. DPH was found to increase the accumulation of SER in fish tissues relative to SER-alone exposure. In addition, the mixture of SER and DPH significantly changed the activities of antioxidant enzymes and led to significant increases in malondialdehyde content, relative to SER alone. Concerning the neurotoxicity, relative to SER-alone exposure, brain AChE activity was significantly enhanced in fish following the combined exposure. Regarding behavioral responses, swimming activity and shoaling behavior were significantly altered in co-exposure treatments compared with the SER alone. Moreover, the inhibition effects on the feeding rates were increased in co-exposure treatments compared to SER alone. Collectively, our results suggest that the mixtures of psychiatric pharmaceuticals may pose more severe ecological risks to aquatic organisms compared to these compounds individually.

An in vivo evaluation of the ontogeny of stereoselective fluoxetine metabolism and disposition in lambs from birth to one year of age

1. The objective was to determine the ontogeny of stereoselective fluoxetine (FX) disposition in postnatal sheep from newborn to adulthood. 2. Catheters were implanted in a carotid artery and jugular vein. FX was administered intravenously, followed by serial arterial blood and cumulative urine collection. The concentrations of R,S-FX and R,S-norfluoxetine (R,S-NFX) in samples were measured using a validated enantioselective LC/MS/MS analytical method. 3. The metabolism of FX at 4.2 ± 0.4 days was limited compared to adults, but had developed compared to the fetus. Total body clearance (Cl_TB) did not significantly increase up to 33.6 ± 0.9 days, but significantly increased at 98.5 ± 2.0 days, with no further changes up to 397.3 ± 8.5 days. Up to 13.4 ± 0.8 days, the disposition of FX included Phase I metabolism to NFX and trifluoromethylphenol (TFMP), and renal elimination. At 32.9 ± 0.9 days, metabolism included Phase II conjugates of FX and NFX. Renal elimination of these compounds was low. 4. The elimination of FX increased in a non-linear manner during the first year in sheep. The metabolism and disposition of FX and NFX in plasma and urine were stereoselective and this appeared due to both stereoselective protein binding and metabolism.

Postnatal outcomes in lambs exposed antenatally and acutely postnatally to fluoxetine

BACKGROUND

Approximately 1/3 of newborns exposed antenatally to selective serotonin reuptake inhibitors (SSRIs) exhibit poor neonatal adaptation. Although several potential mechanisms have been proposed, the actual mechanism has not been elucidated.

METHODS

We investigated outcomes in neonatal lambs exposed prenatally or postnatally to fluoxetine (FX). Daily FX injections (50 mg) were given intravenously (i.v.) to five pregnant ewes via implanted catheters beginning at 131-132 days gestation (term = 147 days) for 2 weeks. In another group, lambs with implanted vascular catheters had sterile water (n = 9) or FX (1 mg/kg, n = 12) injected i.v. on ~postnatal day (PND) 4.

RESULTS

Prenatal FX-exposed lambs (n = 7) were hyperactive during PND 4 to 14 and their heart rate variability (HRV) was significantly lower than in control lambs (n = 7) on PND 2. In contrast, arterial pressure, heart rate, electrocardiogram, arterial blood gases, pH, glucose, lactate, cortisol, and sleep-activity cycles were not altered following postnatal FX injection.

CONCLUSION

This abnormal postnatal hyperactivity with antenatal FX exposure may reflect increased maturity in terms of locomotory activity. The results suggest that altered brain development may be involved in the poor neonatal adaptation in human infants exposed to FX in utero.

The use of clonidine in elderly patients with delirium; pharmacokinetics and hemodynamic responses

Background

The Oslo Study of Clonidine in Elderly Patients with Delirium (LUCID) is an RCT investigating the effect of clonidine in medical patients > 65 years with delirium. To assess the dosage regimen and safety measures of this study protocol, we measured the plasma concentrations and hemodynamic effects of clonidine in the first 20 patients.

Methods

Patients were randomised to clonidine (n = 10) or placebo (n = 10). The treatment group was given a loading dose (75μg every 3rd hour up to a maximum of 4 doses) to reach steady state, and further 75μg twice daily until delirium free for 2 days, discharge or a maximum of 7 days. Blood pressure (BP) and heart rate (HR) were measured just before every dose. If the systolic BP was < 100 mmHg or HR < 50 beats per minute the next dose was omitted. Plasma concentrations of clonidine were measured 3 h after each drug intake on day 1, just before intake (day 2 and at steady state day 4–6) and 3 h after intake at steady state (C_max). Our estimated pre-specified plasma concentration target range was 0.3–0.7μg/L.

Results

3 h after the first dose of 75μg clonidine, plasma concentration levels rose to median 0.35 (range 0.24–0.40)μg/L. Median trough concentration (C₀) at day 2 was 0.70 (0.47–0.96)μg/L. At steady state, median C₀ was 0.47 (0.36–0.76)μg/L, rising to C_max 0.74 (0.56–0.95)μg/L 3 h post dose. A significant haemodynamic change from baseline was only found at a few time-points during the loading doses within the clonidine group. There was however extensive individual BP and HR variation in both the clonidine and placebo groups, and when comparing the change scores (delta values) between the clonidine and the placebo groups, there were no significant differences.

Conclusions

The plasma concentration of clonidine was at the higher end of the estimated therapeutic range. Hemodynamic changes during clonidine treatment were as expected, with trends towards lower blood pressure and heart rate in patients treated with clonidine, but with dose adjustments based on SBP this protocol appears safe.

Trial registration

ClinicalTrials.gov NCT01956604, 09.25.2013. EudraCT Number: 2013–000815-26, 03.18.2013. Enrolment of first participant: 04.24.2014.

Discontinuation and dose adjustment of metoprolol after metoprolol-paroxetine/fluoxetine co-prescription in Dutch elderly

Purpose

Co‐prescription of paroxetine/fluoxetine (a strong CYP2D6 inhibitor) in metoprolol (a CYP2D6 substrate) users is common, but data on the clinical consequences of this drug‐drug interaction are limited and inconclusive. Therefore, we assessed the effect of paroxetine/fluoxetine initiation on the existing treatment with metoprolol on the discontinuation and dose adjustment of metoprolol among elderly.

Methods

We performed a cohort study using the University of Groningen IADB.nl prescription database (www.IADB.nl). We selected all elderly (≥60 years) who had ever been prescribed metoprolol and had a first co‐prescription of paroxetine/fluoxetine, citalopram (weak CYP2D6 inhibitor), or mirtazapine (negative control) from 1994 to 2015. The exposure group was metoprolol and paroxetine/fluoxetine co‐prescription, and the other groups acted as controls. The outcomes were early discontinuation and dose adjustment of metoprolol. Logistic regression was applied to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI).

Results

Combinations of metoprolol‐paroxetine/fluoxetine, metoprolol‐citalopram, and metoprolol‐mirtazapine were started in 528, 673, and 625 patients, respectively. Compared with metoprolol‐citalopram, metoprolol‐paroxetine/fluoxetine was not significantly associated with the early discontinuation and dose adjustment of metoprolol (OR = 1.07, 95% CI:0.77‐1.48; OR = 0.87, 95% CI:0.57‐1.33, respectively). In comparison with metoprolol‐mirtazapine, metoprolol‐paroxetine/fluoxetine was associated with a significant 43% relative increase in early discontinuation of metoprolol (OR = 1.43, 95% CI:1.01‐2.02) but no difference in the risk of dose adjustment. Stratified analysis by gender showed that women have a significantly high risk of metoprolol early discontinuation (OR = 1.62, 95% CI:1.03‐2.53).

Conclusion

Paroxetine/fluoxetine initiation in metoprolol prescriptions, especially for female older patients, is associated with the risk of early discontinuation of metoprolol.

The burden and management of cytochrome P450 2D6 (CYP2D6)-mediated drug-drug interaction (DDI): co-medication of metoprolol and paroxetine or fluoxetine in the elderly

PURPOSE

Metoprolol and paroxetine/fluoxetine are inevitably co-prescribed because cardiovascular disorders and depression often coexist in the elderly. This leads to CYP2D6-mediated drug-drug interactions (DDI). Because systematic evaluations are lacking, we assessed the burden of metoprolol-paroxetine/fluoxetine interaction in the elderly and how these interactions are managed in Dutch community pharmacies.

METHOD

Dispensing data were collected from the University of Groningen pharmacy database (IADB.nl, 1999-2014) for elderly patients (≥60 years) starting beta-blockers and/or antidepressants. Based on the two main DDI alert systems (G-Standard and Pharmabase), incidences were divided between signalled (metoprolol-fluoxetine/paroxetine) and not-signalled (metoprolol-alternative antidepressants and alternative beta-blockers-paroxetine/fluoxetine) combinations. Incident users were defined as patients starting at least one signalled or a non-signalled combination. G-Standard signalled throughout the study period, whereas Pharmabase stopped after 2005.

RESULTS

A total of 1763 patients had 2039 metoprolol-paroxetine/fluoxetine co-prescriptions, despite DDI alert systems, and about 57.3% were signalled. The number of metoprolol-alternative antidepressant combinations (incidences = 3150) was higher than alternative beta-blocker-paroxetine/fluoxetine combinations (incidences = 1872). Metoprolol users are more likely to be co-medicated with an alternative antidepressant (incidences = 2320) than paroxetine/fluoxetine users (incidences = 1232) are. The number of paroxetine/fluoxetine users co-prescribed with alternative beta-blockers was comparable to those co-medicated with metoprolol (about 50%). Less than 5% of patients received a substitute therapy after using metoprolol-paroxetine/fluoxetine. Most of the metoprolol users (90%) received a low dose (mean DDD = 0.47) regardless whether they were prescribed paroxetine/fluoxetine.

CONCLUSION

Despite the signalling software, metoprolol-paroxetine/fluoxetine combinations are still observed in the elderly population. The clinical impact of these interactions needs further investigation. Copyright © 2017 John Wiley & Sons, Ltd.

CYP2D6 polymorphisms and their influence on risperidone treatment

Cytochrome P450 enzyme especially CYP2D6 plays a major role in biotransformation. The interindividual variations of treatment response and toxicity are influenced by the polymorphisms of this enzyme. This review emphasizes the effect of CYP2D6 polymorphisms in risperidone treatment in terms of basic knowledge, pharmacogenetics, effectiveness, adverse events, and clinical practice. Although the previous studies showed different results, the effective responses in risperidone treatment depend on the CYP2D6 polymorphisms. Several studies suggested that CYP2D6 polymorphisms were associated with plasma concentration of risperidone, 9-hydroxyrisperidone, and active moiety but did not impact on clinical outcomes. In addition, CYP2D6 poor metabolizer showed more serious adverse events such as weight gain and prolactin than other predicted phenotype groups. The knowledge of pharmacogenomics of CYP2D6 in risperidone treatment is increasing, and it can be used for the development of personalized medication in term of genetic-based dose recommendation. Moreover, the effects of many factors in risperidone treatment are still being investigated. Both the CYP2D6 genotyping and therapeutic drug monitoring are the important steps to complement the genetic-based risperidone treatment.

Characterization of oxycodone in vitro metabolism by human cytochromes P450 and UDP-glucuronosyltransferases

The hepatic metabolism of oxycodone by cytochromes P450 (CYP) and the UDP-glucuronosyltransferases (UGT), the main metabolic enzymes of phase I and phase II, respectively, was assessed in vitro. The N-demethylation by CYP3A4/5 and the O-demethylation by CYP2D6 in human liver microsomes (HLM) followed Michaelis-Menten kinetics, with intrinsic clearances of 1.46μL/min/mg and 0.35μL/min/mg, respectively. Although noroxycodone and oxymorphone mainly contribute to the elimination of oxycodone, the simulated total in vivo clearance using in vitro phase I metabolism was underestimated. For the first time, metabolism of oxycodone by UGT was deeply investigated using HLM, recombinant enzymes and selective inhibitors. Oxycodone-glucuronide was mainly produced by UGT2B7 (K_m=762±153μM, V_max=344±20 peak area/min/mg) and to a lesser extent by UGT2B4 (K_m=2454±497μM, V_max=201±19 peak area/min/mg). Finally, the kinetics of the drug-drug interactions were assessed using two CYP and UGT cocktail approaches. Incubations of HLM with phase I and phase II drug probes showed that oxycodone mainly decreased the in vitro activities of CYP2D6, CYP3A4/5, UGT1A3, UGT1A6 and UGT2B subfamily with an important impact on UGT2B7.

Pre-clinical evaluation of CYP 2D6 dependent drug-drug interactions between primaquine and SSRI/SNRI antidepressants

Background

The liver-stage anti-malarial activity of primaquine and other 8-aminoquinoline molecules has been linked to bio-activation through CYP 2D6 metabolism. Factors such as CYP 2D6 poor metabolizer status and/or co-administration of drugs that inhibit/interact with CYP 2D6 could alter the pharmacological properties of primaquine.

Methods

In the present study, the inhibitory potential of the selective serotonin reuptake inhibitor (SSRI) and serotonin norepinephrine reuptake inhibitor (SNRI) classes of antidepressants for CYP 2D6-mediated primaquine metabolism was assessed using in vitro drug metabolism and in vivo pharmacological assays.

Results

The SSRI/SNRI classes of drug displayed a range of inhibitory activities on CYP 2D6-mediated metabolism of primaquine in vitro (IC₅₀ 1–94 μM). Fluoxetine and paroxetine were the most potent inhibitors (IC₅₀ ~1 µM) of CYP 2D6-mediated primaquine metabolism, while desvenlafaxine was the least potent (IC₅₀ ~94 µM). The most potent CYP 2D6 inhibitor, fluoxetine, was chosen to investigate the potential pharmacological consequences of co-administration with primaquine in vivo. The pharmacokinetics of a CYP 2D6-dependent primaquine metabolite were altered upon co-administration with fluoxetine. Additionally, in a mouse malaria model, co-administration of fluoxetine with primaquine reduced primaquine anti-malarial efficacy.

Conclusions

These results are the first from controlled pre-clinical experiments that indicate that primaquine pharmacological properties can be modulated upon co-incubation/administration with drugs that are known to interact with CYP 2D6. These results highlight the potential for CYP 2D6-mediated drug–drug interactions with primaquine and indicate that the SSRI/SNRI antidepressants could be used as probe molecules to address the primaquine-CYP 2D6 DDI link in clinical studies. Additionally, CYP 2D6-mediated drug–drug interactions can be considered when examining the possible causes of human primaquine therapy failures.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1329-z) contains supplementary material, which is available to authorized users.

CYP450 genotype and pharmacogenetic association studies: a critical appraisal

Despite strong pharmacological support, association studies using genotype-predicted phenotype as a variable have yielded conflicting or inconclusive evidence to promote personalized pharmacotherapy. Unless the patient is a genotypic poor metabolizer, imputation of patient's metabolic capacity (or metabolic phenotype), a major factor in drug exposure-related clinical response, is a complex and highly challenging task because of limited number of alleles interrogated, population-specific differences in allele frequencies, allele-specific substrate-selectivity and importantly, phenoconversion mediated by co-medications and inflammatory co-morbidities that modulate the functional activity of drug metabolizing enzymes. Furthermore, metabolic phenotype and clinical outcomes are not binary functions; there is large intragenotypic and intraindividual variability. Therefore, the ability of association studies to identify relationships between genotype and clinical outcomes can be greatly enhanced by determining phenotype measures of study participants and/or by therapeutic drug monitoring to correlate drug concentrations with genotype and actual metabolic phenotype. To facilitate improved analysis and reporting of association studies, we propose acronyms with the prefixes ‘g’ (genotype-predicted phenotype) and ‘m’ (measured metabolic phenotype) to better describe this important variable of the study subjects. Inclusion of actually measured metabolic phenotype, and when appropriate therapeutic drug monitoring, promises to reveal relationships that may not be detected by using genotype alone as the variable.

Inhibition of Efavirenz Metabolism by Sertraline and Nortriptyline and Their Effect on Efavirenz Plasma Concentrations

Between 22 and 45% of HIV-positive subjects are likely to report symptoms of depression. Considering this background, a potential pharmacokinetic interaction between the nonnucleoside reverse transcriptase inhibitor efavirenz (EFV) and two antidepressants, sertraline (SRT) and nortriptyline (NT), was studied. Rats were administered EFV alone or together with the antidepressants, and changes in the plasma levels and pharmacokinetic parameters of EFV were analyzed. Additional in vitro experiments with rat and human hepatic microsomes were carried out to evaluate the inhibitory effect of SRT and NT on EFV metabolism by determining the formation rate of the major EFV metabolite (8-OH-EFV). In vivo studies showed similar increases in the plasma levels of EFV when it was coadministered with SRT or NT. However, the studies using rat hepatic microsomes showed a more potent inhibitory effect of NT than of SRT on the metabolism of EFV, with values for the 50% inhibition constant (IC50) and inhibitory constant (Ki) for NT about 9-fold lower than those for SRT. An equation was deduced that explains the similar in vivo effects of SRT and NT in spite of the different in vitro performance data. Using human hepatic microsomes, the strongest inhibitory effect was observed with SRT. In summary, pharmacokinetic interactions between EFV, SRT, and NT, associated with the inhibition of hepatic metabolism of EFV, have been detected in rats. Both antidepressants also inhibit EFV metabolism in human hepatic microsomes, but additional in vivo studies in humans are required to evaluate the clinical implication of this interaction.

Effects of paroxetine, a CYP2D6 inhibitor, on the pharmacokinetic properties of hydrocodone after coadministration with a single-entity, once-daily, extended-release hydrocodone tablet

PURPOSE

A single-entity, once-daily, extended-release formulation of hydrocodone bitartrate (HYD) has been developed for the management of moderate to severe chronic pain. Hydrocodone undergoes cytochrome P-450 (CYP)-mediated metabolism involving the CYP3A4 and CYP2D6 isozymes. CYP3A4 yields norhydrocodone, a major inactive metabolite, whereas CYP2D6 yields hydromorphone, a minor active metabolite. This study examined the influence of the coadministration of paroxetine, a strong selective CYP2D6 inhibitor, on the pharmacokinetic properties of hydrocodone (and hydromorphone) in healthy adults.

METHODS

In this randomized, double-blind, 2-period, 2-treatment crossover study, 24 healthy subjects received paroxetine 20 mg or placebo once daily for 12 days and an HYD 20-mg tablet on day 10 of each period.

FINDINGS

Hydrocodone mean Cmax and t½ and median Tmax values were similar with paroxetine or placebo coadministration (16.8 vs 15.9 ng/mL, 8.5 vs 8.4 hours, and 18.0 vs 18.0 hours, respectively), as were mean AUC0-t and AUC0-∞ values (342.9 vs 325.3 ng · h/mL and 346.3 vs 328.5 ng · h/mL). The 90% CIs of the geometric mean ratios of the hydrocodone AUC and Cmax values were fully within the predetermined range of 80% to 125%, suggesting that there was no effect of multiple doses of paroxetine on systemic exposure to hydrocodone. Mean hydromorphone AUC0-t and Cmax values were decreased with paroxetine versus placebo (0.64 vs 3.8 ng · h/mL and 0.06 vs 0.19 ng/mL), whereas Tmax values remained similar (18.0 vs 16.1 hours, respectively). The mean hydromorphone AUC0-∞ value could not be calculated. Both regimens were well tolerated; after HYD administration, the numbers of adverse events were similar between the 2 treatment regimens, and all adverse events were mild.

IMPLICATIONS

In this study, the coadministration of single-dose HYD with paroxetine at steady state did not alter systemic exposure to hydrocodone, suggesting that HYD can be coadministered with CYP2D6 inhibitors at therapeutic doses, without dosage modification.

COMBINED MIRTAZAPINE AND SSRI TREATMENT OF PTSD: A PLACEBO-CONTROLLED TRIAL

BACKGROUND

Combined treatment with a selective serotonin reuptake inhibitor (SSRI) plus mirtazapine has shown superior efficacy in some studies of depression, but has not been studied in posttraumatic stress disorder (PTSD). This study aimed to assess acceptability of combined sertraline plus mirtazapine treatment for PTSD and to estimate its effect size relative to sertraline plus placebo.

METHODS

Thirty-six adults with PTSD were randomized to 24 weeks of double-blind treatment with sertraline plus mirtazapine or sertraline plus placebo. Outcomes were analyzed with mixed effects models.

RESULTS

The combined treatment group showed a significantly greater remission rate (P = .042) and improvement in depressive symptoms (P = .023) than the sertraline plus placebo group. There were no significant group differences in the two primary outcomes of treatment retention and PTSD severity, or in other secondary outcomes (sleep impairment, sexual functioning, quality of life, and physical and mental functioning), but the combined treatment group showed numerical advantages on all of these outcomes, and effect sizes relative to sertraline plus placebo ranged from small to moderate (d = .26-.63). Both treatments were well-tolerated, with significantly increased appetite but not weight gain in the combined treatment group.

CONCLUSION

Findings suggest that combined treatment of PTSD with sertraline plus mirtazapine may have clinically meaningful advantages in symptomatic improvement, relative to SSRI treatment alone, and acceptable tolerability. Combined treatment with an SSRI plus mirtazapine in PTSD deserves additional study as initial treatment or as an augmentation strategy for nonresponders to an SSRI.

Altering metabolic profiles of drugs by precision deuteration: reducing mechanism-based inhibition of CYP2D6 by paroxetine

Selective deuterium substitution as a means of ameliorating clinically relevant pharmacokinetic drug interactions is demonstrated in this study. Carbon-deuterium bonds are more stable than corresponding carbon-hydrogen bonds. Using a precision deuteration platform, the two hydrogen atoms at the methylenedioxy carbon of paroxetine were substituted with deuterium. The new chemical entity, CTP-347 [(3S,4R)-3-((2,2-dideuterobenzo[d][1,3]dioxol-5-yloxy)methyl)-4-(4-fluorophenyl)piperidine], demonstrated similar selectivity for the serotonin receptor, as well as similar neurotransmitter uptake inhibition in an in vitro rat synaptosome model, as unmodified paroxetine. However, human liver microsomes cleared CTP-347 faster than paroxetine as a result of decreased inactivation of CYP2D6. In phase 1 studies, CTP-347 was metabolized more rapidly in humans and exhibited a lower pharmacokinetic accumulation index than paroxetine. These alterations in the metabolism profile resulted in significantly reduced drug-drug interactions between CTP-347 and two other CYP2D6-metabolized drugs: tamoxifen (in vitro) and dextromethorphan (in humans). Our results show that precision deuteration can improve the metabolism profiles of existing pharmacotherapies without affecting their intrinsic pharmacologies.

Fluoxetine: juvenile pharmacokinetics in a nonhuman primate model

RATIONALE

The selective serotonin reuptake inhibitor (SSRI) fluoxetine is the only psychopharmacological agent approved for use in children. While short-term studies of side effects have been performed, long-term consequences for brain development are not known. Such studies can be performed in appropriate animal models if doses modeling therapeutic use in children are known.

OBJECTIVES

The goal of this study was to identify a daily dose of fluoxetine in juvenile monkeys which would result in serum fluoxetine and norfluoxetine concentrations in the therapeutic range for children.

METHODS

Juvenile (2.5-year-old rhesus monkeys, n = 6) received single administration of doses of 1, 2, and 4 mg/kg day fluoxetine on a background of chronic dosing at an intermediate level to provide steady-state conditions to model therapeutic administration. Using nonlinear modeling, standard pharmacokinetic parameters were derived. Cerebrospinal fluid monoamine neurotransmitters were assayed to confirm the pharmacological effects.

RESULTS

Dose-dependent area under the curve (AUC) and C max values were seen, while T max and absorption/elimination half-lives were minimally influenced by dose. A dosage of 2 mg/kg day given over a 14-week period led to steady-state serum concentrations of active agent (fluoxetine + norfluoxetine) similar to those recorded from drug monitoring studies in children. Cisternal cerebrospinal fluid concentrations of serotonin increased significantly over the 14-week period, while concentrations of the serotonin metabolite (5-HIAA) were lower but not significantly different.

CONCLUSIONS

A dose of 2 mg/kg day fluoxetine in juvenile rhesus monkeys provides an internal dose similar to therapeutic use in children and will help establish a valuable animal model for understanding fluoxetine's therapeutic and potential adverse effects in children.

Risperidone metabolic ratio as a biomarker of individual CYP2D6 genotype in schizophrenic patients

PURPOSE

The purpose of the present study was to investigate the predictive value of the risperidone metabolic ratio for the individual CYP2D6 genotype.

METHODS

The determination of risperidone, 9-hydroxyrisperidone, and CYP2D6 genotype was performed in 89 schizophrenic patients. The receiver operator characteristic (ROC) method and the area under the ROC curve (AUC) were used to illustrate the predictive value of risperidone metabolic ratio for the individual CYP2D6 genotype. The area under the ROC curve (AUC) was used as a global measure of this predictive value. To evaluate the proposed cutoff levels of >1 and <0.1 to identify individuals with a poor or ultrarapid CYP2D6 genotype the sensitivity, specificity, positive predictive value and negative predictive were calculated.

RESULTS

The area under the ROC curve (AUC) for poor and ultrarapid metabolisers was 0.85 and 0.86, respectively. The sensitivity, specificity, positive predictive value and negative predictive value of a risperidone/9-OH-risperidone ratio >1 to CYP2D6 poor metaboliser genotype were 75 %, 95 %, 60 % and 97 %, respectively. The corresponding measures for a metabolic ratio < 0.1 to predict ultrarapid metabolisers were 80 %, 77 %, 18 % and 98 %.

CONCLUSIONS

A metabolic ratio > 1 or < 0.1 may be a useful therapeutic biomarker to recommend CYP2D6 genetic testing to guide the present or future treatment of patients in need of psychotropic drugs.

Are health technology assessments of pharmacogenetic tests feasible? A case study of CYP2D6 testing in the treatment of breast cancer with tamoxifen

This paper reports the process and experience of the design and conduct of a UK-based health technology assessment (HTA) of CYP2D6 pharmacogenetic testing to inform the targeted use of tamoxifen for the treatment of breast cancer. Examples of particular challenges for conducting a HTA are highlighted. It is clear from the HTA process described here that a common finding of similar future HTAs will have gaps in the evidence base, particularly in relation to evidence to inform cost–effectiveness. The lack of evidence is likely to be sufficiently large to result in extreme uncertainty and possibly decisions not to recommend a pharmacogenetic test for use in clinical practice. This has clear negative implications, which may hamper moving pharmacogenetic tests from the research environment into clinical practice and requires attention from both manufacturers of pharmacogenetic tests and key decision-makers responsible for market authorization and reimbursement.

Pharmacokinetic properties of once-daily oral low-dose mesylate salt of paroxetine (LDMP 7.5 mg) following single and multiple doses in healthy postmenopausal women

BACKGROUND

Low-dose mesylate salt of paroxetine (LDMP 7.5 mg) is being investigated for the treatment of vasomotor symptoms associated with menopause.

OBJECTIVE

This Phase I, open-label, single- and multiple-dose study evaluated the pharmacokinetic properties, safety and tolerability of LDMP in postmenopausal, nonsmoking women aged ≥40 years.

METHODS

After a 3-week screening period, subjects received LDMP 7.5-mg capsules as a single dose on day 1 and then as multiple doses (once daily for 14 days) on Days 6-19. Blood samples were collected predose and up to 120 hours postdose on day 1 (single-dose pharmacokinetic profile), at predose (after 12 doses) on day 18, and at predose and up to 24 hours postdose on day 19 (multiple-dose pharmacokinetic profile). Capsules were taken with 240 mL of water while subjects were fasted. Safety was evaluated throughout the study.

RESULTS

Twenty-four women (mean age, 56 years) completed the study. On day 1, median Tmax was ~6 hours, and mean t1/2 was 17.30 hours. Mean plasma concentrations attained predose on days 18 and 19 (days 13 and 14 of multiple dosing) and at 24 hours postdose (day 20) were similar, suggesting that steady state was achieved by day 13 of multiple dosing after 12 daily doses. Mean AUC0-24 h at steady state (day 14 of multiple dosing) was ~3-fold greater than AUC0-∞ on day 1, indicating nonlinear pharmacokinetics. Mean Cmax on day 14 of multiple dosing was ~5-fold greater than that attained on day 1, and the accumulation index (AUCday 19/AUCday 1) at steady state was 9.71. Fluctuation index (calculated as [(Cmax - Cmin)/Cavg ss] × 100) was 75.8%. Most subjects (23/24 [95.8%]) experienced at least 1 treatment-emergent adverse event (AE); however, most AEs (67 events in 22/24 subjects [91.7%]) were mild, and the remainder were moderate. Seventeen subjects experienced 33 AEs that were deemed possibly or probably related to LDMP. No serious AEs were reported, and no clinically meaningful changes in laboratory values, vital signs, or ECGs were observed.

CONCLUSIONS

On multiple dosing, LDMP exhibited nonlinear pharmacokinetics and was well tolerated in these healthy postmenopausal women; the extent of accumulation was consistent with data from the published literature.

Scientific challenges and implementation barriers to translation of pharmacogenomics in clinical practice

The mapping of the human genome and subsequent advancements in genetic technology had provided clinicians and scientists an understanding of the genetic basis of altered drug pharmacokinetics and pharmacodynamics, as well as some examples of applying genomic data in clinical practice. This has raised the public expectation that predicting patients' responses to drug therapy is now possible in every therapeutic area, and personalized drug therapy would come sooner than later. However, debate continues among most stakeholders involved in drug development and clinical decision-making on whether pharmacogenomic biomarkers should be used in patient assessment, as well as when and in whom to use the biomarker-based diagnostic tests. Currently, most would agree that achieving the goal of personalized therapy remains years, if not decades, away. Realistic application of genomic findings and technologies in clinical practice and drug development require addressing multiple logistics and challenges that go beyond discovery of gene variants and/or completion of prospective controlled clinical trials. The goal of personalized medicine can only be achieved when all stakeholders in the field work together, with willingness to accept occasional paradigm change in their current approach.

Antidepressants, metoprolol and the risk of bradycardia

Case reports and pharmacologic theory suggest that some antidepressants can interfere with the hepatic metabolism of metoprolol by cytochrome P450 2D6 (CYP2D6), potentially increasing the risk of bradycardia. The objective of this study was to characterize the clinical consequences of this potential drug interaction at the population level. We conducted a population-based, nested case-control study of Ontario residents 66 years of age or older receiving metoprolol. Cases hospitalized for bradycardia were compared with matched controls (4:1) to explore the odds ratio for initiation of antidepressants that inhibit CYP2D6 (fluoxetine and paroxetine) and those that do not inhibit CYP2D6 (fluvoxamine, citalopram, venlafaxine, and sertraline) 30 days before hospitalization. From April 1997 to March 2009, we identified 332,254 older patients continuously receiving metoprolol, of whom 8232 (2.5%) were treated in hospital for bradycardia. The adjusted odds ratio for exposure to fluoxetine or paroxetine compared with other antidepressants 30 days prior to hospitalization for bradycardia was 0.76 (95% confidence interval 0.42-1.37). Among older patients receiving metoprolol, the initiation of antidepressants that inhibit CYP2D6 was not associated with a significant increase in the risk of bradycardia compared with antidepressants that do not inhibit CYP2D6.

Adjunctive sleep medications and depression outcome in the treatment of serotonin-selective reuptake inhibitor resistant depression in adolescents study

OBJECTIVE

In the Treatment of Resistant Depression in Adolescents, study participants who received medication for sleep had a lower response rate. This report sought to clarify this finding.

METHOD

Depressed adolescents who had not responded to a previous adequate serotonin-selective reuptake inhibitor (SSRI) trial were randomly assigned to another SSRI, venlafaxine, another SSRI+cognitive behavior therapy (CBT), or venlafaxine+CBT. Augmentation with sleep medication was permitted as clinically indicated.

RESULTS

Youth who received trazodone were six times less likely to respond than those with no sleep medication (adjusted odds ratio [OR]=0.16, 95% confidence interval [CI]: 0.05-0.50, p=0.001) and were three times more likely to experience self-harm (OR=3.0, 95% CI: 1.1-7.9, p=0.03), even after adjusting for baseline differences associated with trazodone use. None (0/13) of those cotreated with trazodone and either paroxetine or fluoxetine responded. In contrast, those treated with other sleep medications had similar rates of response (60.0% vs. 50.4%, χ(2)=0.85, p=0.36) and of self-harm events (OR=0.5, 95% CI: 0.1-2.6, p=0.53) as those who received no sleep medication.

CONCLUSIONS

These findings should be interpreted cautiously because these sleep agents were not assigned randomly, but at clinician discretion. Nevertheless, they suggest that the use of trazodone for the management of sleep difficulties in adolescent depression should be re-evaluated and that future research on the management of sleep disturbance in adolescent depression is needed. The very low response rate of participants cotreated with trazodone and either fluoxetine or paroxetine could be due to inhibition of CYP 2D6 by these antidepressants.

Fluoxetine counteracts the cognitive and cellular effects of 5-fluorouracil in the rat hippocampus by a mechanism of prevention rather than recovery

5-Fluorouracil (5-FU) is a cytostatic drug associated with chemotherapy-induced cognitive impairments that many cancer patients experience after treatment. Previous work in rodents has shown that 5-FU reduces hippocampal cell proliferation, a possible mechanism for the observed cognitive impairment, and that both effects can be reversed by co-administration of the antidepressant, fluoxetine. In the present study we investigate the optimum time for administration of fluoxetine to reverse or prevent the cognitive and cellular effects of 5-FU.

Male Lister-hooded rats received 5 injections of 5-FU (25 mg/kg, i.p.) over 2 weeks. Some rats were co-administered with fluoxetine (10 mg/kg/day, in drinking water) for 3 weeks before and during (preventative) or after (recovery) 5-FU treatment or both time periods (throughout). Spatial memory was tested using the novel location recognition (NLR) test and proliferation and survival of hippocampal cells was quantified using immunohistochemistry. 5-FU-treated rats showed cognitive impairment in the NLR task and a reduction in cell proliferation and survival in the subgranular zone of the dentate gyrus, compared to saline treated controls. These impairments were still seen for rats administered fluoxetine after 5-FU treatment, but were not present when fluoxetine was administered both before and during 5-FU treatment. The results demonstrate that fluoxetine is able to prevent but not reverse the cognitive and cellular effects of 5-FU. This provides information on the mechanism by which fluoxetine acts to protect against 5-FU and indicates when it would be beneficial to administer the antidepressant to cancer patients.

Depression screening and patient outcomes in cancer: a systematic review

Background

Several practice guidelines recommend screening for depression in cancer care, but no systematic reviews have examined whether there is evidence that depression screening benefits cancer patients. The objective was to evaluate the potential benefits of depression screening in cancer patients by assessing the (1) accuracy of depression screening tools; (2) effectiveness of depression treatment; and (3) effect of depression screening, either alone or in the context of comprehensive depression care, on depression outcomes.

Methods

Data sources were CINAHL, Cochrane, EMBASE, ISI, MEDLINE, PsycINFO and SCOPUS databases through January 24, 2011; manual journal searches; reference lists; citation tracking; trial registry reviews. Articles on cancer patients were included if they (1) compared a depression screening instrument to a valid criterion for major depressive disorder (MDD); (2) compared depression treatment with placebo or usual care in a randomized controlled trial (RCT); (3) assessed the effect of screening on depression outcomes in a RCT.

Results

There were 19 studies of screening accuracy, 1 MDD treatment RCT, but no RCTs that investigated effects of screening on depression outcomes. Screening accuracy studies generally had small sample sizes (median = 17 depression cases) and used exploratory methods to set sample-specific cutoff scores that varied substantially across studies. A nurse-delivered intervention for MDD reduced depressive symptoms moderately (effect size = 0.37).

Conclusions

The one treatment study reviewed reported modest improvement in depressive symptoms, but no evidence was found on whether or not depression screening in cancer patients, either alone or in the context of optimal depression care, improves depression outcomes compared to usual care. Depression screening in cancer should be evaluated in a RCT in which all patients identified as depressed, either through screening or via physician recognition and referral in a control group, have access to comprehensive depression care.

CYP2D6 genotyping and tamoxifen: an unfinished story in the quest for personalized medicine

The philosophy behind personalized medicine is that each patient has a unique biologic profile that should guide the choice of therapy, resulting in an improved treatment outcome, ideally with reduced toxicity. Thus, there has been increasing interest in identifying genetic variations that are predictive of a drug's efficacy or toxicity. Although it is one of the most effective drugs for treating breast cancer, tamoxifen is not effective in all estrogen receptor (ER)-positive breast cancer patients, and it is frequently associated with side effects, such as hot flashes. Relative resistance to tamoxifen treatment may be a result, in part, from impaired drug activation by cytochrome P450 2D6 (CYP2D6). Indeed, recent studies have identified allelic variations in CYP2D6 to be an important determinant of tamoxifen's activity (and toxicity). This article will summarize the current information regarding the influence of the major genotypes and CYP2D6 inhibitors on tamoxifen metabolism, with a focus on its clinical utility and the current level of evidence for CYP2D6 genotyping of patients who are candidates for tamoxifen treatment.

Pharmacogenetics of endocrine therapy for breast cancer

The selective estrogen receptor modulator tamoxifen has been used for more than three decades for the treatment, and more recently prevention, of breast cancer in women of all ages. The conversion of tamoxifen to active metabolites involves several cytochrome P450 (CYP) enzymes. CYP2D6 is the key enzyme responsible for the conversion of N-desmethyl tamoxifen to endoxifen. Single nucleotide polymorphisms in the CYP2D6 gene are not uncommon, and some alleles code for enzymes with reduced, null, or increased activity. Multiple studies suggest that women who carry one or two variant CYP2D6 alleles that encode enzymes with null or reduced activity may have an inferior breast cancer outcome when treated with tamoxifen in the adjuvant setting compared to women carrying two alleles encoding an enzyme with normal activity. Unfortunately, the data are not uniformly concordant, and definitive evidence that would change routine clinical practice is not yet available. CYP2D6 activity can also be reduced by concomitant use of drugs that inhibit the enzyme, including antidepressants used for psychiatric conditions or to relieve hot flashes, and these should be avoided in tamoxifen users whenever possible. Emerging data suggest that host factors may also predict interpatient variability in response to aromatase inhibitors.

Predictors of risperidone and 9-hydroxyrisperidone serum concentration in children and adolescents

INTRODUCTION

Little is known about risperidone metabolism in a clinical sample, where polypharmacy is common. Such knowledge is important since several of its side effects are dose dependent.

METHODS

Medically healthy patients aged 7 to 17 years old treated with risperidone for at least 6 months were enrolled. Trough serum risperidone and 9-hydroxyrisperidone concentrations were measured.

RESULTS

One hundred seven participants (92% males) were recruited, representing a heterogenous clinical group with attention-deficit/hyperactivity disorder, disruptive behavior disorders, pervasive developmental disorders, anxiety disorders, mood disorders, tic disorders, or psychotic disorders. Risperidone had been used at a mean dose of 0.03 mg/kg, for a mean 2.5 years, predominantly to treat irritability and aggression. Cytochrome CYP2D6 inhibitors were divided into prominent (fluoxetine, bupropion, and lamotrigine), intermediate (sertraline), and weak inhibition groups (citalopram or escitalopram). The concentrations of risperidone and its metabolite were strongly associated with the dose of risperidone and time since the last dose and, to a lesser extent, with male sex. In addition, risperidone concentration increased with pubertal stage (p < 0.05), while body mass index z-score (p = 0.001) predicted a higher 9-hydroxyrisperidone concentration. The use of CYP2D6 inhibitors was much more strongly associated with risperidone concentration (p < 0.0001) than with its metabolite's (p = 0.06).

CONCLUSIONS

In chronically treated youths, the metabolism of risperidone depends on the stage of sexual development, whereas that of 9-hydroxyrisperidone varies with body fat. Moreover, CYP2D6 inhibitors more strongly affect risperidone metabolism than that of its metabolite. The clinical implications of these findings, in relation to efficacy and tolerability, deserve further investigation.

Impact of multiple inhibitors or substrates of cytochrome P450 2D6 on plasma risperidone levels in patients on polypharmacy

Studies that focus on multidrug interactions in natural settings are sparse. In this investigation, data from therapeutic drug monitoring (TDM) were used to study the impact of multiple cytochrome P450 enzyme (CYP) 2D6 substrates and inhibitors on plasma risperidone levels. CYP2D6 catalyzes the conversion of risperidone to the active metabolite 9-OH-risperidone. The question whether CYP2D6 activity is important for the level of the "active moiety" (ie, the sum of risperidone and 9-OH-risperidone) is controversial. Concentration-to-dose (C:D) ratios of risperidone and 9-OH-risperidone in 218 patients were associated with the number of concomitantly used substrates or inhibitors of CYP2D6. The C:D ratios of risperidone in patients with 0, 1, and >1 numbers of CYP2D6 inhibitors were 2.6, 8.5, and 17 nmol L mg, respectively. Differences between the groups were highly significant (P < 0.001). All patients with >1 CYP2D6 inhibitors were administered at least 1 potent CYP2D6 inhibitor, that is fluoxetine, paroxetine, thioridazine, and/or levomepromazine. The C:D ratios of the active moiety (risperidone + 9-OH-risperidone) in patients with 0, 1, and >1 numbers of concomitant CYP2D6 inhibitors were 17, 24, and 30 nmol L mg, respectively (P = 0.001), which was explained by higher levels of risperidone without any change in the levels of 9-OH-risperidone. Concomitant use of 1 or several drugs recognized as substrates for CYP2D6, without any proven inhibitory effect, had no apparent influence on the levels of risperidone or 9-OH-risperidone, suggesting that the risk of drug-drug interactions between different substrates of CYP2D6 is low when used in therapeutic doses. In conclusion, the results suggest that an increase in the number of concomitant inhibitors may be associated with a lower CYP2D6 activity, although the type of inhibitor is probably more important. Drug-dependent inhibition of CYP2D6 increases the active moiety of risperidone. An indication for risperidone TDM should therefore include concomitant medication with established CYP inhibitors.

An evaluation of the drug interaction potential of pazopanib, an oral vascular endothelial growth factor receptor tyrosine kinase inhibitor, using a modified Cooperstown 5+1 cocktail in patients with advanced solid tumors

Pazopanib, an oral inhibitor of vascular endothelial growth factor receptor, platelet-derived growth factor receptor, and c-kit kinases, inhibits multiple cytochrome P450 (CYP450) enzymes in vitro. This study in patients with advanced cancer evaluated the effect of pazopanib on CYP450 function by comparing the pharmacokinetics of CYP-specific probe drugs in the presence and absence of pazopanib. The probes used included midazolam (CYP3A specific), warfarin (CYP2C9 specific), omeprazole (CYP2C19 specific), caffeine (CYP1A2 specific), and dextromethorphan (CYP2D6 specific). The estimated ratios of the geometric means (90% confidence interval (CI)) for the area under the curve to the last measurable point (AUC(0-t)) for these probe drugs with/without pazopanib were as follows: midazolam, 1.35 (1.18-1.54); omeprazole, 0.81 (0.59-1.12); caffeine, 1.00 (0.77-1.30); and S-warfarin, 0.93 (0.84-1.03). The geometric least-squares (LS) mean ratio of urine dextromethorphan:dextrorphan ranged from 1.33 (0-4-h interval) to 1.64 (4-8-h interval). The data suggest that pazopanib is a weak inhibitor of CYP3A4 and CYP2D6 and has no effect on CYP1A2, CYP2C9, and CYP2C19 in patients with advanced cancer.

Selective serotonin reuptake inhibitors and breast cancer mortality in women receiving tamoxifen: a population based cohort study

OBJECTIVE

To characterise whether some selective serotonin reuptake inhibitor (SSRI) antidepressants reduce tamoxifen's effectiveness by inhibiting its bioactivation by cytochrome P450 2D6 (CYP2D6).

DESIGN

Population based cohort study.

PARTICIPANTS

Women living in Ontario aged 66 years or older treated with tamoxifen for breast cancer between 1993 and 2005 who had overlapping treatment with a single SSRI.

MAIN OUTCOME MEASURES

Risk of death from breast cancer after completion of tamoxifen treatment, as a function of the proportion of time on tamoxifen during which each SSRI had been co-prescribed.

RESULTS

Of 2430 women treated with tamoxifen and a single SSRI, 374 (15.4%) died of breast cancer during follow-up (mean follow-up 2.38 years, SD 2.59). After adjustment for age, duration of tamoxifen treatment, and other potential confounders, absolute increases of 25%, 50%, and 75% in the proportion of time on tamoxifen with overlapping use of paroxetine (an irreversible inhibitor of CYP2D6) were associated with 24%, 54%, and 91% increases in the risk of death from breast cancer, respectively (P<0.05 for each comparison). By contrast, no such risk was seen with other antidepressants. We estimate that use of paroxetine for 41% of tamoxifen treatment (the median overlap in our sample) would result in one additional breast cancer death within five years of cessation of tamoxifen for every 19.7 (95% confidence interval 12.5 to 46.3) patients so treated; the risk with more extensive overlap would be greater.

CONCLUSION

Paroxetine use during tamoxifen treatment is associated with an increased risk of death from breast cancer, supporting the hypothesis that paroxetine can reduce or abolish the benefit of tamoxifen in women with breast cancer.