Selective serotonin reuptake inhibitors and CNS drug interactions. A critical review of the evidence

Optimizing antidepressant and clozapine co-prescription in clinical practice: A systematic review and expert recommendations

OBJECTIVES

To synthesize the information relevant for clinical practice on clozapine-antidepressant co-prescription concerning pharmacokinetic drug-drug interactions (DDI), adverse drug reactions (ADRs) associated with the co-prescription, antidepressant add-on for clozapine-resistant symptoms and antidepressant add-on for clozapine-induced ADRs.

METHODS

Articles were identified with MEDLINE, Web of Sciences and PsycINFO search from inception through April 2023. Data were synthesized narratively.

RESULTS

ADRs are most often induced by the co-prescription of antidepressants that inhibit CYP enzymes (fluvoxamine, fluoxetine, paroxetine). Fluvoxamine add-on is hazardous because of its potent inhibition of clozapine metabolism and has few indications (lowering daily number of clozapine tablets, reducing norclozapine-induced metabolic disturbances and other dose-dependent clozapine-induced ADRs). ADR frequency may be reduced by therapeutic drug monitoring and knowledge of other factors impacting clozapine metabolism (pneumonia, inflammation, smoking, etc.). Improvement of negative symptoms is the most documented beneficial effect of antidepressant add-on for clozapine-resistant psychotic symptoms. The add-on antidepressant should be chosen according to its safety profile regarding DDI with clozapine: antidepressants inhibiting clozapine metabolism or increasing the anticholinergic load should be avoided. Other indications of antidepressant add-on (affective or obsessive compulsive symptoms, sialorrhea, and enuresis) are poorly documented.

CONCLUSION

Antidepressant add-on to clozapine is associated with potential benefits in clozapine users as this strategy may contribute to reduce the burden of clozapine-resistant symptoms or of clozapine-induced ADRs. Further studies are needed to determine whether antidepressant add-on can reduce the risk of clozapine discontinuation.

COVID-19 Outcomes: Does the Use of Psychotropic Drugs Make a Difference? Accumulating Evidence of a Beneficial Effect of Antidepressants-A Scoping Review

PURPOSE/BACKGROUND

Studies for repurposed drugs in severe acute respiratory syndrome coronavirus type 2-infected and coronavirus disease 2019 (COVID-19) patients are ongoing. According to preclinical research, antidepressants (ADs) might be useful in the treatment of COVID-19.

METHODS/PROCEDURES

We conducted a scoping review including clinical studies on AD effects on SARS-CoV-2 infection and COVID-19.

FINDING/RESULTS

As of January 2, 2022, we found 14 clinical studies, which could be included into this review. Among them, there were 2 randomized, placebo-controlled studies and 2 prospective parallel-group studies about the efficacy/effectiveness and tolerability of fluvoxamine. The remaining studies were mainly retrospective studies considering COVID-19 hospital populations predominantly exposed to fluoxetine (N = 3), other selective serotonin reuptake inhibitors (SSRI), selective norepinephrine reuptake inhibitors (SNRI), and trazodone. The vast majority were hospital studies and assessed COVID-19 severity (morbidity) and mortality as primary endpoints. The only outpatient study (fluvoxamine) investigated the COVID-19-related hospitalization rate, and 1 psychiatric hospital study (SSRI, SNRI, trazodone) focused on the SARS-CoV-2 infection rate.

IMPLICATIONS/CONCLUSIONS

At present, the best evidence of an "anti-COVID-19" potential of ADs exists for fluvoxamine and, to a lesser extent, for fluoxetine. Preliminary evidence had found that patients exposed to SSRI or SNRI substance classes might have a reduced mortality risk and that trazodone might reduce SARS-CoV-2 infection rates. Three studies found no relevant influence of ADs on COVID-19 morbidity and mortality, and 1 study described increased mortality. The latter study, however, did not differentiate between psychotropic medication and ADs. Tricyclics and monoamine oxidase inhibitors are still absolute "dark zones" in COVID-19 research. Further controlled studies testing the effectiveness/efficacy and tolerability/safety (as well as the treatment timing and duration) of different AD substance classes in COVID-19 and post/long-COVID patients of various populations are warranted.

Design, synthesis, structural and molecular characterization, toxicity, psychotropic activity and molecular docking evaluation of a novel phenytoin derivative: 3-decyl-5,5-diphenylimidazolidine-2,4-dione

The hydantoin scaffold is of substantial importance and it is commonly used in drug discovery. Herein, we report the synthesis of a novel phenytoine (a hydantoin derivative) with high yield by the reaction of phenytoin with 1-bromodecyl agent. Namely, 3-decyl-5,5- diphenylimidazolidine-2,4-dione (3DDID). The optimized geometry of the compound was calculated using density functional theory (DFT) method by B3LYP with 6-311++G(d,p) basis set. For this calculation, the X-ray data were used as initial values. Molecular electrostatic potential (MEP) surface and Frontier molecular orbitals (FOMs) were prepared for the compound. The crystal structure of the title compound contains intermolecular N-H···O, C-H···O hydrogen bonds and weak C-H···π interactions. Hirshfeld surface analysis and 2D fingerprint plots of the molecule aid comparison of intermolecular interactions and these analysis reveals that two close contacts are associated with intermolecular hydrogen bonds. The psychotropic activity evaluation of the synthesized compound was further explored using hole bored test for exploratory behaviors, dark//light box test for anxiolytic activity and Rota-road, traction, chimney testes were used to assess the myrelaxant effect. In addition, molecular modeling study was also conducted to rationalize the potential as neurotherapeutic drugs of our synthesized compound by predicting their binding modes, binding affinities and optimal orientation at the active site of the GABA-A receptor and Na⁺ channel. Finally, in silico ADMET predictions was also examined. HighlightsSynthesis, structural, and molecular characterization of a novel phenytoin derivative.DFT, XRD, and the Hirshfeld surface analysis of crystal structure was studied.Acute toxicity and psychotropic activity evaluation of 3-decyl-5,5 diphenylimidazolidine-2,4-dione (3DDID).Molecular modeling studies have been conducted to rationalize the obtained data and to determine the probable binding mode.Communicated by Ramaswamy H. Sarma.

Transcutaneous electrical acupoint stimulation for post-traumatic stress disorder: Assessor-blinded, randomized controlled study

AIM

Transcutaneous electrical acupoint stimulation (TEAS) has the potential to alleviate post-traumatic stress disorder (PTSD). The purpose of this study was to determine whether adding TEAS to sertraline or cognitive behavioral therapy (CBT) could improve the anti-PTSD efficacy.

METHODS

In this randomized controlled trial, 240 PTSD patients (60 in each group) were assigned to receive simulated TEAS combined with sertraline (group A) or with CBT (group B), active TEAS combined with CBT (group C), or active TEAS combined with CBT plus sertraline (group D) for 12 weeks. The outcomes were measured using the Clinician-Administered PTSD Scale, PTSD Check List-Civilian Version, and 17-item Hamilton Rating Scale for Depression.

RESULTS

While PTSD symptoms reduced over time in all patients, groups C and D had markedly greater improvement in both PTSD and depressive measures than groups A and B in all post-baseline measurement points, with moderate to very large effect sizes of 0.484-2.244. Groups C and D also had a significantly higher rate than groups A and B on clinical response (85.0% and 95.0% vs 63.3% and 60.0%, P < 0.001) and on remission (15.0% and 25.0% vs 3.3% and 1.7%, P < 0.001). The incidence of adverse events was similar between groups A and D and between groups B and C.

CONCLUSIONS

Additional TEAS augments the anti-PTSD and antidepressant efficacy of antidepressants or CBT, without increasing the incidence of adverse effects. TEAS could serve as an effective intervention for PTSD and comorbid depression. This trial was registered with www.chictr.org (no.: ChiCTR1800017255).

Cardiovascular Events Following Treatment Initiation with Atypical Antipsychotic Medications in Publicly Insured U.S. Youth

OBJECTIVE

To assess the risk of incident cardiovascular events that led to hospitalizations or emergency department visits following atypical antipsychotic (AAP) treatment initiation in youth according to dose, duration of use, and concomitant use of leading psychotropic medication classes.

METHODS

We used computerized Medicaid claims to conduct a retrospective cohort study of youth (5-20 years) who initiated AAP treatment. AAP use was operationalized in a time-dependent manner according to current vs. former use, average daily dose (in risperidone dose equivalents), and duration of use. In a secondary analysis, concomitant use of (1) stimulants and (2) serotonin-reuptake inhibitors (SSRI/SNRIs) with AAPs was also assessed. To account for confounding, disease risk score methodology was used in discrete time failure models.

RESULTS

There were 74,700 youth who initiated AAP treatment (average follow-up = 24.8 months). During follow-up, the risk of cardiovascular events was significantly greater during current than former AAP use (RR = 1.55, 95% CI = 1.09-2.21). Furthermore, for current users of AAPs, the risk of cardiovascular events intensified with average daily dose (RR = 2.04, 95% CI = 1.11-3.77 for >3.75 mg/day vs. ≤1.25 mg/day). The risk of cardiovascular events did not significantly differ according to duration of AAP use. In AAP-treated youth, concomitant SSRI/SNRI use was associated with an increased risk of cardiovascular events (RR = 1.61, 95% CI = 1.01-2.57). By contrast, stimulant use concomitant with AAPs was not significantly associated with an increased risk of cardiovascular events.

CONCLUSIONS

In publicly insured U.S. youth, current AAP use was associated with an increased risk of incident cardiovascular events, which intensified with increasing dose and with concomitant SSRI/SNRI use. Prudent interpretation of these findings suggests that further research is needed to identify youth subpopulations with the greatest risk of developing AAP treatment-emergent cardiovascular events.

Selective serotonin reuptake inhibitor use in pregnant women; pharmacogenetics, drug-drug interactions and adverse effects

INTRODUCTION

Possible negative effects of selective serotonin reuptake inhibitors (SSRIs) in pregnancy relate to congenital anomalies, negative perinatal events and neurodevelopmental outcome. Many studies are confounded by the underlying maternal disease and by pharmacogenetic and pharmacokinetic differences of these drugs. Areas covered: The possible interactions of SSRIs and serotonin and norepinephrine reuptake inhibitors with other drugs and the known effects of SSRIs on congenital anomalies, perinatal and neurodevelopmental outcome. Expert opinion: SSRIs should be given with caution when combined with other drugs that are metabolized by cytochrome P450 enzymes. SSRIs apparently increase the rate of severe cardiac malformations, induce neonatal adaptation problems in up to 30% of the offspring, increase the rate of persistent pulmonary hypertension of the newborn and possibly slightly increase the rate of prematurity and low birth weight. Most neurodevelopmental follow up studies did not find significant cognitive impairments except some transient gross motor delay, slight impairment of language abilities and possibly behavioral changes. The literature on the possible association of SSRIs with autism spectrum disorder is inconsistent; if an association exists, it is apparently throughout pregnancy. The risk associated with treatment discontinuation seems to outweigh the risk of treatment, as severe maternal depression may negatively affect the child's development. If needed, treatment should continue in pregnancy with the minimal effective dose.

The impact of pharmacists' input to reduce serotonin syndrome drug interactions in an Australian hospital

BACKGROUND

Drug interactions contribute significantly to adverse-related events and hospital admissions. Example of common drug interactions includes combinations of medications that induces serotonin syndrome. Pharmacists are well placed in the multidisciplinary team to alert prescribers of these drug interactions and offer an alternative management.

OBJECTIVE

The objective is to evaluate the effectiveness of pharmacists' input in preventing patients being discharged on clinically relevant drug interactions that have the potential to cause serotonin syndrome in an Australian hospital.

METHOD

A retrospective cross-sectional audit of patients' case notes who were prescribed a combination of drugs likely to induce serotonin syndrome on admission were examined over a 3-month period. A predefined list of serotonin syndrome-inducing drugs of severity 1 and 2 was used to search for patients on these drug combinations on admission. The severities of the drug combinations were classified as per the Monthly Index of Medical Specialties drug interactions guide. Subsequent pharmacists' interventions were recorded on discharge to observe any change in prescribing practice. Descriptive statistics were used to analyze the data. P values were obtained using the Student's t-test and Fisher's exact tests.

RESULTS

A total of 144 patients over 3 months were identified to have been prescribed a combination of drugs with a potential to cause serotonin syndrome during admission. Of these patients, 79 and 21% were prescribed combination of serotonergic drugs that were classified as severity 1 and 2, respectively, according to Monthly Index of Medical Specialties. A total of 56% (n = 81) of the audited patients were discharged with no serotonin syndrome-inducing drug combinations and 44% (n = 63) were discharged on serotonin syndrome-inducing drug combinations of severity 1 or 2. Pharmacist input has led to a significant reduction (relative risk reduction 44%; P < 0.0001) in the total number of patients who were discharged on severity 1 and 2 serotonin syndrome-inducing drug combinations. There were 87 patients (60%) who had a pharmacist input during admission. In this subset of the cohort, 36% (n = 31) of patients were discharged on serotonin syndrome-inducing drug combinations (combined both severity 1 and 2) compared with 56% (n = 32) in those who did not get a pharmacist input, P = 0.017. In addition, 64% (n = 56) of patients in this group were discharged on no serotonin syndrome-inducing drug combinations compared with 44% (n =  25) in the nonpharmacist group, P = 0.017.

CONCLUSION

The audit highlights the pharmacists' role in significantly reducing clinically relevant drug interaction in patients prescribed serotonin syndrome-inducing drug combination in a single-center Australian hospital on discharge.

Retrospective use of PBPK modelling to understand a clinical drug-drug interaction between dextromethorphan and GSK1034702

1. In a clinical trial, a strong drug-drug interaction (DDI) was observed between dextromethorphan (DM, the object or victim drug) and GSK1034702 (the precipitant or perpetrator drug), following single and repeat doses. This study determined the inhibition parameters of GSK1034702 in vitro and applied PBPK modelling approaches to simulate the clinical observations and provide mechanistic hypotheses to understand the DDI. 2. In vitro assays were conducted to determine the inhibition parameters of human CYP2D6 by GSK1034702. PBPK models were populated with the in vitro parameters and DDI simulations conducted and compared to the observed data from a clinical study with DM and GSK1034702. 3. GSK1034702 was a potent direct and metabolism-dependent inhibitor of human CYP2D6, with inhibition parameters of: IC₅₀=1.6 μM, K_inact = 3.7 h^-1 and K_I = 0.8 μM. Incorporating these data into PBPK models predicted a DDI after repeat, but not single, 5 mg doses of GSK1034702. 4. The DDI observed with repeat administration of GSK1034702 (5 mg) can be attributed to metabolism-dependent inhibition of CYP2D6. Further, in vitro data were generated and several potential mechanisms proposed to explain the interaction observed following a single dose of GSK1034702.

Influence of the selective antagonist of the NR2B subunit of the NMDA receptor, traxoprodil, on the antidepressant-like activity of desipramine, paroxetine, milnacipran, and bupropion in mice

Pre-clinical and clinical studies indicated that a blockade of the NMDA receptor complex creates new opportunities for the treatment of affective disorders, including depression. The aim of the present study was to assess the influence of traxoprodil (10 mg/kg) on the activity of desipramine (10 mg/kg), paroxetine (0.5 mg/kg), milnacipran (1.25 mg/kg), and bupropion (10 mg/kg), each at sub-therapeutic doses. Moreover, brain levels of traxoprodil and tested agents were determined using HPLC. The obtained results were used to ascertain the nature of occurring interaction between traxoprodil and studied antidepressants. The experiment was carried out on naïve adult male Albino Swiss mice. Traxoprodil and other tested drugs were administered intraperitoneally. The influence of traxoprodil on the activity of selected antidepressants was evaluated in forced swim test (FST). Locomotor activity was estimated to exclude false positive/negative data. To assess the influence of traxoprodil on the concentration of used antidepressants, their levels were determined in murine brains using HPLC. Results indicated that traxoprodil potentiated activity of all antidepressants examined in FST and the observed effects were not due to the increase in locomotor activity. Only in the case of co-administration of traxoprodil and bupropion, increased bupropion concentrations in brain tissue were observed. All tested agents increased the traxoprodil levels in the brain. Administration of a sub-active dose of traxoprodil with antidepressants from different chemical groups, which act via enhancing monoaminergic transduction, caused the antidepressant-like effect in FST in mice. The interactions of traxoprodil with desipramine, paroxetine, milnacipran, and bupropion occur, at least partially, in the pharmacokinetic phase.

Enantioselective analysis of fluoxetine in pharmaceutical formulations by capillary zone electrophoresis

Fluoxetine is an antidepressant, a selective serotonin reuptake inhibitor (SSRI) used primarily in the treatment of major depression, panic disorder and obsessive compulsive disorder. Chiral separation of racemic fluoxetine is necessary due to its enantioselective metabolism. In order to develop a suitable method for chiral separation of fluoxetine, cyclodextrin (CD) modified capillary electrophoresis (CE) was employed. A large number of native and derivatized, neutral and ionized CD derivatives were screened to find the optimal chiral selector. As a result of this process, heptakis(2,3,6-tri-O-methyl)-β-CD (TRIMEB) was selected for enantiomeric discrimination. A factorial analysis study was performed by orthogonal experimental design in which several factors are varied at the same time to optimize the separation method. The optimized method (50 mM phosphate buffer, pH = 5.0, 10 mM TRIMEB, 15 °C, + 20 kV, 50 mbar/1 s, detection at 230 nm) was successful for baseline separation of fluoxetine enantiomers within 5 min. Our method was validated according to ICH guidelines and proved to be sensitive, linear, accurate and precise for the chiral separation of fluoxetine.

Nanomedicine in Central Nervous System (CNS) Disorders: A Present and Future Prospective

Purpose: For the past few decades central nervous system disorders were considered as a major strike on human health and social system of developing countries. The natural therapeutic methods for CNS disorders limited for many patients. Moreover, nanotechnology-based drug delivery to the brain may an exciting and promising platform to overcome the problem of BBB crossing. In this review, first we focused on the role of the blood-brain barrier in drug delivery; and second, we summarized synthesis methods of nanomedicine and their role in different CNS disorder. Method: We reviewed the PubMed databases and extracted several kinds of literature on neuro nanomedicines using keywords, CNS disorders, nanomedicine, and nanotechnology. The inclusion criteria included chemical and green synthesis methods for synthesis of nanoparticles encapsulated drugs and, their in-vivo and in-vitro studies. We excluded nanomedicine gene therapy and nanomaterial in brain imaging. Results: In this review, we tried to identify a highly efficient method for nanomedicine synthesis and their efficacy in neuronal disorders. SLN and PNP encapsulated drugs reported highly efficient by easily crossing BBB. Although, these neuro-nanomedicine play significant role in therapeutics but some metallic nanoparticles reported the adverse effect on developing the brain. Conclusion: Although impressive advancement has made via innovative potential drug development, but their efficacy is still moderate due to limited brain permeability. To overcome this constraint,powerful tool in CNS therapeutic intervention provided by nanotechnology-based drug delivery methods. Due to its small and biofunctionalization characteristics, nanomedicine can easily penetrate and facilitate the drug through the barrier. But still, understanding of their toxicity level, optimization and standardization are a long way to go.

An evaluation of the CYP2D6 and CYP3A4 inhibition potential of metoprolol metabolites and their contribution to drug-drug and drug-herb interaction by LC-ESI/MS/MS

The aim of the present study was to evaluate the contribution of metabolites to drug-drug interaction and drug-herb interaction using the inhibition of CYP2D6 and CYP3A4 by metoprolol (MET) and its metabolites. The peak concentrations of unbound plasma concentration of MET, α-hydroxy metoprolol (HM), O-desmethyl metoprolol (ODM) and N-desisopropyl metoprolol (DIM) were 90.37 ± 2.69, 33.32 ± 1.92, 16.93 ± 1.70 and 7.96 ± 0.94 ng/mL, respectively. The metabolites identified, HM and ODM, had a ratio of metabolic area under the concentration-time curve (AUC) to parent AUC of ≥0.25 when either total or unbound concentration of metabolite was considered. In vitro CYP2D6 and CYP3A4 inhibition by MET, HM and ODM study revealed that MET, HM and ODM were not inhibitors of CYP3A4-catalyzed midazolam metabolism and CYP2D6-catalyzed dextromethorphan metabolism. However, DIM only met the criteria of >10% of the total drug related material and <25% of the parent using unbound concentrations. If CYP inhibition testing is solely based on metabolite exposure, DIM metabolite would probably not be considered. However, the present study has demonstrated that DIM contributes significantly to in vitro drug-drug interaction. Copyright © 2016 John Wiley & Sons, Ltd.

Drug-drug interactions and QT prolongation as a commonly assessed cardiac effect - comprehensive overview of clinical trials

Background

Proarrhythmia assessment is one of the major concerns for regulatory bodies and pharmaceutical industry. ICH guidelines recommending preclinical tests have been established in attempt to eliminate the risk of drug-induced arrhythmias. However, in the clinic, arrhythmia occurrence is determined not only by the inherent property of a drug to block ion currents and disturb electrophysiological activity of cardiac myocytes, but also by many other factors modifying individual risk of QT prolongation and subsequent proarrhythmia propensity. One of those is drug-drug interactions. Since polypharmacy is a common practice in clinical settings, it can be anticipated that there is a relatively high risk that the patient will receive at least two drugs mutually modifying their proarrhythmic potential and resulting either in triggering the occurrence or mitigating the clinical symptoms. The mechanism can be observed either directly at the pharmacodynamic level by competing for the molecular targets, or indirectly by modifying the physiological parameters, or at the pharmacokinetic level by alteration of the active concentration of the victim drug.

Methods

This publication provides an overview of published clinical studies on pharmacokinetic and/or pharmacodynamic drug-drug interactions in humans and their electrophysiological consequences (QT interval modification). Databases of PubMed and Scopus were searched and combinations of the following keywords were used for Title, Abstract and Keywords fields: interaction, coadministration, combination, DDI and electrocardiographic, QTc interval, ECG. Only human studies were included. Over 4500 publications were retrieved and underwent preliminary assessment to identify papers accordant with the topic of this review. 76 papers reporting results for 96 drug combinations were found and analyzed.

Results

The results show the tremendous variability of drug-drug interaction effects, which makes one aware of complexity of the problem, and suggests the need for assessment of an additional risk factors and careful ECG monitoring before administration of drugs with anticipated QT prolongation.

Conclusions

DDIs can play significant roles in drugs’ cardiac safety, as evidenced by the provided examples. Assessment of the pharmacodynamic effects of the drug interactions is more challenging as compared to the pharmacokinetic due to the significant diversity in the endpoints which should be analyzed specifically for various clinical effects. Nevertheless, PD components of DDIs should be accounted for as PK changes alone do not allow to fully explain the electrophysiological effects in clinic situations.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-016-0053-1) contains supplementary material, which is available to authorized users.

Adverse drug reactions in a psychiatric department of tertiary care teaching hospital in India: Analysis of spontaneously reported cases

The epidemiological data are limited for the spontaneous adverse drug reaction (ADR) reporting system in psychiatry and its comparison with intensive monitoring studies in terms of causative drugs, seriousness, preventability and drug interactions. This spontaneous ADR reporting study was carried out over a period of three years in the psychiatry department. We adopted WHO definition for an ADR, Naranjo's algorithm for causality, WHO-ADR terminology for the labeling of involved organ-system, International conference on harmonisation (ICH) E2A guidelines for seriousness, modified Schumock and Thornton's criteria for preventability and Medscape drug interaction checker for drug interactions. Two subgroup analyses were performed to find out the risk factors for the serious and preventable reactions. A total of 97 ADRs from 67 patients were included for analysis. The incidence of 'overall' and 'serious ADRs were 0.69% (95% CI: 0.54%, 0.88%) and 0.18% (95% CI: 0.12-0.29%), respectively. The females experienced more ADRs than males. The most commonly reported ADR, incriminated pharmacology group and drug, were extrapyramidal movement disorders (22.68%), atypical antipsychotics (35.62%) and escitalopram (13.91%), respectively. One out of five and one out three reactions were considered as 'serious' and 'preventable', respectively. The drug interactions contributed in 34.02% reactions. The factors significantly associated with 'serious' reactions were typical antipsychotics [OR: 5.47 (1.68, 17.87)], central and peripheral nervous system disorders [OR: 24.00 (5.12, 112.5)] and extrapyramidal reactions [OR: 14.03 (4.43, 44.43)]. The polypharmacy [OR: 5.85 (1.90, 18.03)] was significantly associated with 'preventable' reactions. The spontaneous reporting system is efficient to detect serious reactions and preventable reactions.

Pharmacological management of chronic neuropathic pain: revised consensus statement from the Canadian Pain Society

BACKGROUND

Neuropathic pain (NeP), redefined as pain caused by a lesion or a disease of the somatosensory system, is a disabling condition that affects approximately two million Canadians.

OBJECTIVE

To review the randomized controlled trials (RCTs) and systematic reviews related to the pharmacological management of NeP to develop a revised evidence-based consensus statement on its management.

METHODS

RCTs, systematic reviews and existing guidelines on the pharmacological management of NeP were evaluated at a consensus meeting in May 2012 and updated until September 2013. Medications were recommended in the consensus statement if their analgesic efficacy was supported by at least one methodologically sound RCT (class I or class II) showing significant benefit relative to placebo or another relevant control group. Recommendations for treatment were based on the degree of evidence of analgesic efficacy, safety and ease of use.

RESULTS

Analgesic agents recommended for first-line treatments are gabapentinoids (gabapentin and pregabalin), tricyclic antidepressants and serotonin noradrenaline reuptake inhibitors. Tramadol and controlled-release opioid analgesics are recommended as second-line treatments for moderate to severe pain. Cannabinoids are now recommended as third-line treatments. Recommended fourth-line treatments include methadone, anticonvulsants with lesser evidence of efficacy (eg, lamotrigine, lacosamide), tapentadol and botulinum toxin. There is support for some analgesic combinations in selected NeP conditions.

CONCLUSIONS

These guidelines provide an updated, stepwise approach to the pharmacological management of NeP. Treatment should be individualized for each patient based on efficacy, side-effect profile and drug accessibility, including cost. Additional studies are required to examine head-to-head comparisons among analgesics, combinations of analgesics, long-term outcomes and treatment of pediatric, geriatric and central NeP.

Interaction of different antidepressants with acute and chronic methadone in mice, and possible clinical implications

We studied the interaction of a single dose of different antidepressant medications with a single (acute) dose or implanted mini-pump (chronic) methadone administration in mice, using the hotplate assay. For the acute experiment, subthreshold doses of six antidepressant drugs were administered separately with a single dose of methadone. The addition of a subthreshold dose of desipramine or clomipramine to methadone produced significant augmentation of the methadone effect with each drug (p < 0.05). Fluvoxamine given at a fixed subthreshold dose induced a synergistic effect only with a low methadone dose. Escitalopram, reboxetine and venlafaxine given separately, each at a fixed subthreshold dose, induced no interaction. Possible clinical implications of these findings are that while escitalopram, reboxetine and venlafaxine do not affect methadone's antinociception in mice and are safe to be given together with methadone when indicated, fluvoxamine, clomipramine and desipramine considerably augment methadone-induced effects and should be avoided in this population due to the risk of inducing opiate overdose. For the chromic experiment, when a subthreshold dose of either escitalopram, desipramine or clomipramine was injected to mice following 2 weeks of methadone administration with the mini-pump, none of the antidepressant drugs strengthened methadone's analgesic effect. Further studies are needed before possible clinical implications can be drawn.

An unusual case of risperidone instability in a fatality presenting an analytical and interpretative challenge

This paper describes the detection and characterization of unusual metabolite/breakdown products of the anti-psychotic drug risperidone in post-mortem blood and urine as part of a toxicological investigation into an unexpected death of a male suffering from paranoid schizophrenia prescribed risperidone and previously paroxetine. Compounds detected in the post-mortem blood and urine specimens were shown to be benzisoxazole ring scission products of risperidone and a hydroxy metabolite. These compounds are never routinely detected in blood and urine but can be present in mammalian faeces indicating that gut bacteria could be responsible for their formation. In this case, evidence for this process was demonstrated by the controlled in vitro stability study of risperidone spiked into the case blood and urine leading to the hypothesis that the post-mortem blood and urine samples analyzed could have contained bacteria with the ability to breakdown risperidone and its metabolite in this way. This finding is very unusual and has not been encountered before in any previous risperidone cases investigated by the authors, or widely reported in the post-mortem toxicological literature. However, a recently published paper has supported these findings in blood. As a result of this work, it was shown that the deceased had taken risperidone prior to death, even in the absence of any risperidone or its hydroxy metabolite(s) in the blood and urine. Given that risperidone has been reported to interact with paroxetine, the ingestion of risperidone could have been a factor that contributed to the death.

A 6-week randomized controlled trial with 4-week follow-up of acupuncture combined with paroxetine in patients with major depressive disorder

Acupuncture possesses the antidepressant potential. In this 6-week randomized controlled trial with 4-week follow-up, 160 patients with major depressive disorder (MDD) were randomly assigned to paroxetine (PRX) alone (n = 48) or combined with 18 sessions of manual acupuncture (MA, n = 54) or electrical acupuncture (EA, n = 58). Treatment outcomes were measured mainly using the 17-item Hamilton Depression Rating Scale (HAMD-17), Self-rating Depression Scale (SDS), clinical response and remission rates. Average PRX dose taken and proportion of patients who required an increased PRX dose due to symptom aggravation were also obtained. Both additional MA and EA produced a significantly greater reduction from baseline in score on HAMD-17 and SDS at most measure points from week 1 through week 6 compared to PRX alone. The clinical response was markedly greater in MA (69.8%) and EA (69.6%) groups than the group treated with PRX alone (41.7%, P = 0.004). The proportion of patients who required an increase dose of PRX due to symptom aggravation was significantly lower with MA (5.7%) and EA (8.9%) than PRX alone (22.9%, P = 0.019). At 4 weeks follow-up after completion of acupuncture treatment, patients with EA, but not MA, continued to show significantly greater clinical improvement. Incidence of adverse events was not different in the three groups. Our study indicates that acupuncture can accelerate the clinical response to selective serotonin reuptake inhibitors (SSRIs) and prevent the aggravation of depression. Electrical acupuncture may have a long-lasting enhancement of the antidepressant effects (Trial Registration: ChiCTR-TRC-08000278).

Pharmacokinetics/Pharmacodynamics of Desloratadine and Fluoxetine in Healthy Volunteers

The authors assessed the potential for a pharmacokinetic/pharmacodynamic interaction between desloratadine and fluoxetine. This randomized, placebo-controlled, open-label study was conducted in 54 healthy volunteers. Subjects received 1 of 3 treatments: desloratadine 5 mg plus fluoxetine 20 mg, desloratadine 5 mg plus placebo, or fluoxetine 20 mg plus placebo. Serial electrocardiograms (ECGs) were performed at baseline and day 35. Treatment effects on C(max) and AUC were assessed. During coadministration of desloratadine with fluoxetine, the ratio of the mean log-transformed C(max) and AUC values for desloratadine following concomitant fluoxetine therapy revealed a small increase in C(max) values of 15% (90% confidence interval [CI], 95%-139%) but no increase for AUC values (90% CI, 82%-123%). Corresponding values for 3-OH desloratadine demonstrated small increases in mean log-transformed C(max) and AUC ratios: 17% (90% CI, 100%-136%) and 13% (90% CI, 96%-132%), respectively. Statistical evaluation of the ratio of the mean C(max) and AUC values for fluoxetine following concomitant desloratadine therapy revealed small decreases of 9% (90% CI, 72%-115%) and 11% (90% CI, 69%-113%), respectively. Corresponding values for norfluoxetine demonstrated modest increases in mean log-transformed C(max) and AUC ratios: 22% (90% CI, 100%-139%) and 18% (90% CI, 101%-136%), respectively. Coadministration of desloratadine with a potent inhibitor of CYP2D6 did not result in clinically relevant changes in its pharmacokinetic parameters. Desloratadine administration was not associated with clinically important changes in the pharmacokinetics of fluoxetine, a drug metabolized by CYP2D6. The most common adverse event in all groups was headache (65%). Desloratadine plus fluoxetine caused no significant changes in ECGs or ventricular rate.

Antidepressant prescribing patterns: a comparison of blacks and whites in a medicaid population

OBJECTIVE

This paper reports results stemming from a retrospective inquiry designed to determine the prescribing pattern of tricyclic antidepressants (TCAs) relative to selective serotonin reuptake inhibitors (SSRIs), and the subsequent effect on regimen adherence among African American (Black) and White beneficiaries enrolled in the state of South Carolina Medicaid programme.

PATIENTS AND METHODS

Adjudicated patient-level paid-claims data for the time-frame 1 January 1990 to 31 December 1994 were abstracted resulting in a statewide cohort of 8596 ambulatory beneficiaries, 18 to 64 years of age, without receipt of antidepressant pharmacotherapy in the 1-year time-frame prior to initiating a regimen of either a TCA or SSRI, and remaining Medicaid-eligible for 1 year thereafter.

RESULTS

Black race [odds ratio (OR) = 1.56, 95% confidence interval (CI) = 1.43 to 1.70], age 40 to 64 years (OR = 1.15, 95% CI = 1.06 to 1.26), and male gender (OR = 1.27, 95% CI = 1.14 to 1.41) were significant predictors of initiating antidepressant pharmacotherapy with a TCA. Relative to Whites, Blacks were found to be less likely to have obtained at least a 3-month (>/=90 days) supply of a TCA (22.1 vs 31.7%) or an SSRI (30.7 vs 36.1%), or to have obtained a 6-month (>/=180 days) supply of a TCA (6.4 vs 10.9%) or an SSRI (8.1 vs 13.2%).

CONCLUSION

Further prospective research is required to discern the reasons for observed differences in prescribing and adherence patterns for antidepressant pharmacotherapy by age, gender and race, and to foster the development of educational programming designed to ensure clinically rational and equitable access to pharmacotherapeutic innovation.

The importance of drug-drug interactions as a cause of adverse drug reactions: a pharmacovigilance study of serotoninergic reuptake inhibitors in France

PURPOSE

To quantify the importance of drug-drug interactions (DDIs) in the occurrence of adverse drug reactions (ADRs) reported with serotoninergic reuptake inhibitors in a pharmacovigilance database.

METHODS

All spontaneous reports of ADRs registered in 2008 by the Midi-Pyrénées PharmacoVigilance Centre that contained mention of one of the serotoninergic reuptake inhibitor (SRI) antidepressants marketed in France were reviewed. DDIs were identified according to the French National Drug Formulary (Vidal) and the interaction supplement of the French independent drug bulletin La Revue Prescrire. ADRs explained by DDIs were characterised.

RESULTS

Among the 2,101 spontaneous reports recorded, 177 involved at least one SRI antidepressant. Among the 156 ADRs with at least one theoretical DDI, 41% (95% confidence interval 34-49%) could be explained by a DDI. The most frequent antidepressant involved in DDIs was escitalopram, followed by fluoxetine and citalopram. Among the 65 ADRs related to DDIs, 37 (52.9%) were "serious", mainly bleedings, confusion and falls, hyponatremia and serotoninergic syndromes. The most frequent drug interactions occurred with psychotropics (antipsychotics, benzodiazepines, among others), followed by antithrombotic agents (antagonists of vitamin K, antiplatelets), diuretics and angiotensin II antagonists. The group with ADRs related to DDIs was older than the group with ADRs not related to DDIs. ADRs were threefold more "serious" in the case of DDIs.

CONCLUSION

Around 40% of ADRs reported with SRIs were related to DDIs. Most of these occurred after association with psychotropics, antithrombotics, or diuretics, especially in the elderly.

The relationship between clinical pharmacokinetics of aripiprazole and CYP2D6 genetic polymorphism: effects of CYP enzyme inhibition by coadministration of paroxetine or fluvoxamine

Purpose

To investigate the effects of coadministration of paroxetine or fluvoxamine on the pharmacokinetics of aripiprazole in healthy adult Japanese with different CYP2D6 genotypes.

Methods

Fourteen CYP2D6 extensive metabolizer (EM) and 14 CYP2D6 intermediate metabolizer (IM) subjects were coadministered a single oral dose of aripiprazole 3 mg after steady-state plasma concentrations of the SSRIs paroxetine (20 mg/day) or fluvoxamine (100 mg/day) were reached by repeated oral doses for 6–7 days. The pharmacokinetics of aripiprazole with and without coadministration of SSRIs were compared according to CYP2D6 genotypes.

Results

Coadministration of paroxetine, a potent CYP2D6 inhibitor, decreased systemic clearance (CL/F) of aripiprazole by 58 and 23% in CYP2D6 EMs and IMs, respectively, demonstrating that the percentage inhibition of CYP2D6 activity by coadministration of paroxetine was apparently greater in CYP2D6 EMs than in IMs. Coadministration of fluvoxamine, a less potent CYP3A4 inhibitor, decreased the CL/F of aripiprazole by 39% in CYP2D6 EMs and 40% in IMs, indicating the same inhibitory effect on CYP enzymes, regardless of the CYP2D6 genotype. Percent contribution of CYP2D6 to total CL/F (CYP2D6 plus CYP3A4) of aripiprazole estimated as a reduced percentage of CL/F by CYP enzyme inhibition was 62% for CYP2D6 EMs and 24% for IMs in paroxetine coadministration, and 40% for CYP2D6 EMs and 18% for IMs in fluvoxamine coadministration.

Conclusions

There were marked differences in the degree of influence of paroxetine coadministration on the pharmacokinetics of aripiprazole between CYP2D6 EMs and IMs, but no apparent differences were found between two CYP2D6 genotypes in fluvoxamine coadministration. Aripiprazole can be used safely in combination with SSRIs that have a CYP enzyme-inhibitory action.

Acute anxiogenic-like effects of selective serotonin reuptake inhibitors are attenuated by the benzodiazepine diazepam in BALB/c mice

Selective serotonin re-uptake inhibitors (SSRIs), which are used commonly to treat anxiety disorders, have characteristic anxiogenic effects following acute administration. Treatment with anxiolytic benzodiazepines (BZs) may reduce these effects, although little is known about potential drug interactions. Our study evaluated acute anxiogenic-like effects of SSRIs, alone and combined with a BZ. Adult male BALB/c mice received fluoxetine (3.0-30.0mg/kg, i.p.) or citalopram (3.0-30.0mg/kg, i.p.) alone or in combination with diazepam (0.3-10.0mg/kg, i.p.), after which they were evaluated with the light/dark and open-field tests for anxiogenesis/anxiolysis. In addition, release of the stress hormone corticosterone was assessed following combined SSRI/BZ administration. In the light/dark and open-field tests, acute SSRIs produced a behavioral profile consistent with anxiogenesis, while diazepam produced an anxiolytic-like profile. Pre-treatment with diazepam (0.3-10mg/kg) reversed the effects of an anxiogenic-like dose of an SSRI (18mg/kg fluoxetine, 30mg/kg citalopram) in both light/dark and open-field tests. Diazepam, fluoxetine or citalopram, and their combination all significantly increased plasma corticosterone levels to the same degree. These findings suggest that a BZ-type drug can attenuate acute anxiogenic-like effects of an SSRI via a mechanism independent of corticosterone regulation.

Effects of cigarette smoking and cytochrome P450 2D6 genotype on fluvoxamine concentration in plasma of Japanese patients

Fluvoxamine is a selective serotonin reuptake inhibitor widely used in the treatment of depression and other psychiatric diseases. The aim of this study was to assess the clinical impact of cigarette smoking on plasma fluvoxamine concentration in Japanese patients, and evaluate whether the cytochrome P450 (CYP) 1A2 and CYP2D6 genotypes have effects on that concentration. Thirty-two Japanese patients receiving fluvoxamine were enrolled. They were maintained on the same daily dose of fluvoxamine (mean + or - S.D., 109.4 + or - 66.2 mg/d) for at least 4 weeks to obtain the steady-state plasma concentration. The steady-state plasma concentration-to-dose (C/D) ratio of fluvoxamine in patients who smoked (n = 6, 11.8 + or - 6.5 ng/ml/dose) was significantly lower than that in non-smoker patients (n = 26, 22.8 + or - 11.2 ng/ml/dose). There was no significant difference for the C/D ratio of fluvoxamine in patients with CYP1A2 -3860G/G, -3860G/A, and -3860A/A between non-smokers and smokers. Among non-smoker patients, the C/D ratios of fluvoxamine in those with one and two mutated alleles of CYP2D6 were 1.6- and 1.4-fold higher, respectively, than those with no mutated alleles, though the differences among those three genotype groups were not significant. Furthermore, stepwise multiple regression analysis revealed that cigarette smoking and daily dose had significant positive correlations with the plasma concentration of fluvoxamine. Our findings suggest that cigarette smoking has a significant impact on the steady-state plasma concentration of fluvoxamine in Japanese patients.

Pharmacogenetic testing and therapeutic drug monitoring are complementary tools for optimal individualization of drug therapy

Genetic factors contribute to the phenotype of drug response, but the translation of pharmacogenetic outcomes into drug discovery, drug development or clinical practice has proved to be surprisingly disappointing. Despite significant progress in pharmacogenetic research, only a few drugs, such as cetuximab, dasatinib, maraviroc and trastuzumab, require a pharmacogenetic test before being prescribed. There are several gaps that limit the application of pharmacogenetics based upon the complex nature of the drug response itself. First, pharmacogenetic tests could be more clinically applicable if they included a comprehensive survey of variation in the human genome and took into account the multigenic nature of many phenotypes of drug disposition and response. Unfortunately, much of the existing research in this area has been hampered by limitations in study designs and the nonoptimal selection of gene variants. Secondly, although responses to drugs can be influenced by the environment, only fragmentary information is currently available on how the interplay between genetics and environment affects drug response. Third, the use of a pharmacogenetic test as a standard of care for drug therapy has to overcome significant scientific, economic, commercial, political and educational barriers, among others, in order for clinically useful information to be effectively communicated to practitioners and patients. Meanwhile, the lack of efficacy is in this process is quite as costly as drug toxicity, especially for very expensive drugs, and there is a widespread need for clinically and commercially robust pharmacogenetic testing to be applied. In this complex scenario, therapeutic drug monitoring of parent drugs and/or metabolites, alone or combined with available pharmacogenetic tests, may be an alternative or complementary approach when attempts are made to individualize dosing regimen, maximize drug efficacy and enhance drug safety with certain drugs and populations (e.g. antidepressants in older people).

The effect of 1-furan-2-yl-3-pyridine-2-yl-propenone on pharmacokinetic parameters of theophylline

The pharmacokinetic parameters of theophylline in rats did not change significantly when the drug was intravenously administered after three consecutive days of pretreatment with 17 mg/kg, orally, of 1-furan-2-yl-3-pyridine-2-yl-propenone (FPP-3), an investigatory drug having dual inhibitory action on cyclooxygenase (COX) and 5-lipoxygenase (5-LOX). However, significant changes were found in the pharmacokinetic parameters of the drug at doses of 34 mg/kg and more of FPP-3. Results of cytochrome P450 activity test indicated that the alteration in pharmacokinetic parameters of the drug appears to be due to the inhibitory effect of FPP-3 on cytochrome P450 1A which is responsible for the metabolism of theophylline. Methoxyresorufin-O-demethylase (MROD) and ethoxyresorufin-O-deethylase (EROD) activity assays revealed that the relative activities of cytochrome P450 1A1 and 1A2 were dose-dependently reduced in the presence of 1, 5, and 10 microM FPP-3 concentrations. Taking into consideration that FPP-3 is intended to be primarily used by geriatric patients with chronic diseases and therefore may be used in long-term basis, the investigatory drug needs to be assessed thoroughly in terms of drug interaction with other commonly prescribed medications.

Prediction of pharmacokinetic drug-drug interaction caused by changes in cytochrome P450 activity using in vivo information

The aim of the present paper was to present an overview of the current status of the methods used to predict the magnitude of pharmacokinetic drug-drug interactions (DDIs) which are caused by apparent changes in cytochrome P450 (CYP) activity with an emphasis on a method using in vivo information. In addition, more than a hundred representative CYP substrates, inhibitor and inducer drugs involved in significant pharmacokinetic DDIs were selected from the literature and are listed. Although the magnitude of DDIs has been conventionally predicted based on in vitro experiments, their predictability is restricted occasionally due to several difficulties, including a precise determination of the unbound inhibitor concentrations at the enzyme site and a reliable in vitro measurement of the inhibition constant (K(i)). Alternatively, a simple method has been recently proposed for the prediction of the magnitude of DDIs based on information fully available from in vivo clinical studies. The new in vivo-based method would be applicable to the adjustment of dose regimens in actual pharmacotherapy situations although it requires a prior clinical study for the prediction. In this review, theoretical and quantitative relationships between the in vivo- and the in vitro-based prediction methods are considered. One of the interesting outcomes of the consideration is that the K(i)-normalized dose (dose/in vitro K(i)) of larger than approximately 20L (2-200L, when variability is considered) may be a pragmatic index which predicts significant in vivo DDIs. In the last part of the article, the relevance of the inclusion of the in vivo-based method into the process of new drug development is discussed for good prediction of in vivo DDIs.

Spirocyclic delta opioid receptor agonists for the treatment of pain: discovery of N,N-diethyl-3-hydroxy-4-(spiro[chromene-2,4'-piperidine]-4-yl) benzamide (ADL5747)

Selective, nonpeptidic delta opioid receptor agonists have been the subject of great interest as potential novel analgesic agents. The discoveries of BW373U86 (1) and SNC80 (2) contributed to the rapid expansion of research in this field. However, poor drug-like properties and low therapeutic indices have prevented clinical evaluation of these agents. Doses of 1 and 2 similar to those required for analgesic activity produce convulsions in rodents and nonhuman primates. Recently, we described a novel series of potent, selective, and orally bioavailable delta opioid receptor agonists. The lead derivative, ADL5859 (4), is currently in phase II proof-of-concept studies for the management of pain. Further structure activity relationship exploration has led to the discovery of ADL5747 (36), which is approximately 50-fold more potent than 4 in an animal model of inflammatory pain. On the basis of its favorable efficacy, safety, and pharmacokinetic profile, 36 was selected as a clinical candidate for the treatment of pain.

Pulmonary embolism from persistent dilatation of the bladder secondary to anticholinergic side effects

OBJECTIVE

To discuss the risk that bladder distention resulting from anticholinergic side effects of antipsychotics can cause iliac vein compression syndrome (IVCS) and subsequent pulmonary embolism (PE).

METHOD

Case report, review of the literature and discussion.

RESULTS

We report the case of a 65-year-old man with depression who experienced PE associated with IVCS due to a distended urinary bladder resulting from anticholinergic side effects. PE disappeared after conservative therapy with heparin followed by warfarin.

CONCLUSION

When drugs with anticholinergic effects are given to immobilized patients such as those with severe depression, close observation including monitoring of urine volume is needed to prevent IVCS caused by drug-induced urinary retention, and subsequent PE.

Effect of smoking and CYP2D6 polymorphisms on the extent of fluvoxamine-alprazolam interaction in patients with psychosomatic disease

PURPOSE

Fluvoxamine (FVX) is metabolized by cytochrome P450 (CYP) 2D6 and CYP1A2 and inhibits CYP3A4. The aim of this study was to investigate the factors responsible for interindividual variability in the extent of interaction between FVX and alprazolam (ALP).

METHODS

Blood samples were taken from 49 depressive patients to determine plasma concentration of FVX, ALP or both. Twenty-four samples were taken during the FVX-alone period, 21 samples during the ALP-alone period and 30 samples during the FVX-ALP period. Subjects were also genotyped for CYP2D6.

RESULTS

The concentration-to-dose (C/D) ratio of ALP during the FVX-treatment period was significantly higher than that during the ALP-alone period. The CYP2D6 genotype affected neither the C/D ratios of FVX nor the extent of interaction. The mean C/D ratio of FVX in smokers was reduced by more than 30% in comparison with that in non-smokers. The mean C/D ratio of ALP in non-smokers was increased by FVX, while that in smokers was unchanged.

CONCLUSIONS

The extent of interaction between FVX and ALP may be affected by smoking, which alters the C/D ratio of FVX. Therefore, when FVX and ALP are concomitantly administered, it should be noted that non-smokers may exhibit greater drug interaction than smokers.

Clinically relevant pharmacokinetic drug interactions with second-generation antidepressants: an update

BACKGROUND

The second-generation antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), and other compounds with different mechanisms of action. All second-generation antidepressants are metabolized in the liver by the cytochrome P450 (CYP) enzyme system. Concomitant intake of inhibitors or inducers of the CYP isozymes involved in the biotransformation of specific antidepressants may alter plasma concentrations of these agents, although this effect is unlikely to be associated with clinically relevant interactions. Rather, concern about drug interactions with second-generation antidepressants is based on their in vitro potential to inhibit > or = 1 CYP isozyme.

OBJECTIVE

The goal of this article was to review the current literature on clinically relevant pharmacokinetic drug interactions with second-generation antidepressants.

METHODS

A search of MEDLINE and EMBASE was conducted for original research and review articles published in English between January 1985 and February 2008. Among the search terms were drug interactions, second-generation antidepressants, newer antidepressants, SSRIs, SNRIs, fluoxetine, paroxetine, fluvoxamine, sertraline, citalopram, escitalopram, venlafaxine, duloxetine, mirtazapine, reboxetine, bupropion, nefazodone, pharmacokinetics, drug metabolism, and cytochrome P450. Only articles published in peer-reviewed journals were included, and meeting abstracts were excluded. The reference lists of relevant articles were hand-searched for additional publications.

RESULTS

Second-generation antidepressants differ in their potential for pharmacokinetic drug interactions. Fluoxetine and paroxetine are potent inhibitors of CYP2D6, fluvoxamine markedly inhibits CYP1A2 and CYP2C19, and nefazodone is a substantial inhibitor of CYP3A4. Therefore, clinically relevant interactions may be expected when these antidepressants are coadministered with substrates of the pertinent isozymes, particularly those with a narrow therapeutic index. Duloxetine and bupropion are moderate inhibitors of CYP2D6, and sertraline may cause significant inhibition of this isoform, but only at high doses. Citalopram, escitalopram, venlafaxine, mirtazapine, and reboxetine are weak or negligible inhibitors of CYP isozymes in vitro and are less likely than other second-generation antidepressants to interact with co-administered medications.

CONCLUSIONS

Second-generation antidepressants are not equivalent in their potential for pharmacokinetic drug interactions. Although interactions may be predictable in specific circumstances, use of an antidepressant with a more favorable drug-interaction profile may be justified.

Role of cytochrome P450 in drug interactions

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.

Identification of human cytochrome P450 enzymes involved in the major metabolic pathway of fluvoxamine

The metabolism of fluvoxamine to fluvoxamino acid is known to involve a two-step oxidation process via an alcohol intermediate, fluvoxamino alcohol. The present study was carried out to identify the cytochrome P450 (CYP) enzyme(s) involved in the metabolism offluvoxamine to fluvoxamino alcohol using human liver microsomes and cDNA-expressed human CYP enzymes. The mean Km and Vmax values for the formation of fluvoxamino alcohol from fluvoxamine in human liver microsomes were 76.3 microM and 37.5 pmol min(-1) mg(-1) protein, respectively. The formation of fluvoxamino alcohol from fluvoxamine in pooled human liver microsomes was significantly inhibited by quinidine, a relatively specific CYP2D6 inhibitor, with a Ki value of 2.2 microM, whereas other several relatively specific CYP inhibitors did not inhibit the formation of fluvoxamino alcohol. In addition, only CYP2D6 of several cDNA-expressed human CYP enzymes examined showed substantial activity for the formation of fluvoxamino alcohol. Furthermore, the formation of fluvoxamino acid from fluvoxamino alcohol is potently inhibited by 4-methylpyrazole in human liver cytosol. These data suggest that CYP2D6 is the only enzyme predominantly responsible for the first-step oxidation of fluvoxamine to fluvoxamino alcohol, and alcohol dehydrogenase is involved in the second-step oxidation of fluvoxamino alcohol to the corresponding carbolic acid.

Pharmacological management of chronic neuropathic pain - consensus statement and guidelines from the Canadian Pain Society

Neuropathic pain (NeP), generated by disorders of the peripheral and central nervous system, can be particularly severe and disabling. Prevalence estimates indicate that 2% to 3% of the population in the developed world suffer from NeP, which suggests that up to one million Canadians have this disabling condition. Evidence-based guidelines for the pharmacological management of NeP are therefore urgently needed. Randomized, controlled trials, systematic reviews and existing guidelines focusing on the pharmacological management of NeP were evaluated at a consensus meeting. Medications are recommended in the guidelines if their analgesic efficacy was supported by at least one methodologically sound, randomized, controlled trial showing significant benefit relative to placebo or another relevant control group. Recommendations for treatment are based on degree of evidence of analgesic efficacy, safety, ease of use and cost-effectiveness. Analgesic agents recommended for first-line treatments are certain antidepressants (tricyclics) and anticonvulsants (gabapentin and pregabalin). Second-line treatments recommended are serotonin noradrenaline reuptake inhibitors and topical lidocaine. Tramadol and controlled-release opioid analgesics are recommended as third-line treatments for moderate to severe pain. Recommended fourth-line treatments include cannabinoids, methadone and anticonvulsants with lesser evidence of efficacy, such as lamotrigine, topiramate and valproic acid. Treatment must be individualized for each patient based on efficacy, side-effect profile and drug accessibility, including cost. Further studies are required to examine head-to-head comparisons among analgesics, combinations of analgesics, long-term outcomes, and treatment of pediatric and central NeP.

Metabolic drug interactions with newer antipsychotics: a comparative review

Newer antipsychotics introduced in clinical practice in recent years include clozapine, risperidone, olanzapine, quetiapine, sertindole, ziprasidone, aripiprazole and amisulpride. These agents are subject to drug-drug interactions with other psychotropic agents or with medications used in the treatment of concomitant physical illnesses. Most pharmacokinetic interactions with newer antipsychotics occur at the metabolic level and usually involve changes in the activity of the major drug-metabolizing enzymes involved in their biotransformation, i.e. the cytochrome P450 (CYP) monooxygenases and/or uridine diphosphate-glucuronosyltransferases (UGT). Clozapine is metabolized primarily by CYP1A2, with additional contribution by other CYP isoforms. Risperidone is metabolized primarily by CYP2D6 and, to a lesser extent, CYP3A4. Olanzapine undergoes both direct conjugation and CYP1A2-mediated oxidation. Quetiapine is metabolized by CYP3A4, while sertindole and aripiprazole are metabolized by CYP2D6 and CYP3A4. Ziprasidone pathways include aldehyde oxidase-mediated reduction and CYP3A4-mediated oxidation. Amisulpride is primarily excreted in the urine and undergoes relatively little metabolism. While novel antipsychotics are unlikely to interfere with the elimination of other drugs, co-administration of inhibitors or inducers of the major enzymes responsible for their metabolism may modify their plasma concentrations, leading to potentially significant effects. Most documented metabolic interactions involve antidepressant and anti-epileptic drugs. Of a particular clinical significance is the interaction between fluvoxamine, a potent CYP1A2 inhibitor, and clozapine. Differences in the interaction potential among the novel antipsychotics currently available may be predicted based on their metabolic pathways. The clinical relevance of these interactions should be interpreted in relation to the relative width of their therapeutic index. Avoidance of unnecessary polypharmacy, knowledge of the interaction profiles of individual agents, and careful individualization of dosage based on close evaluation of clinical response and, possibly, plasma drug concentrations are essential to prevent and minimize potentially adverse drug interactions in patients receiving newer antipsychotics.

Cytochrome P450-catalyzed pathways in human brain: Metabolism meets pharmacology or old drugs with new mechanism of action?

The true importance of cytochrome P450 enzymes, not just in drug metabolism but also in pharmacology, is only beginning to be appreciated. Though originally discovered through their role in the biotransformation of xenobiotics, the P450 enzyme super family is ubiquitous in nature and necessarily evolved around endogenous pathways. The extent of tissue- and cell-specific expression of individual P450 isoforms has led many investigators to hypothesize localized roles in endogenous biochemical pathways for isoforms traditionally thought of as drug-metabolizing. In some cases, direct evidence from humanized transgenic animal models can confirm the degree to which such enzymes modulate endogenous pathways. However, overlapping P450 substrate specificities may mask genetic or biochemical deficiencies, such that many of these reactions appear nonessential. Nonetheless, the drug-induced alteration of local biochemical concentrations in extrahepatic tissues due to metabolism by and inhibition of P450 isoforms has tremendous potential for introducing unexpected pharmacological effects. Nowhere is this truer than in the CNS. On the other hand, if we can harness the power of in silico modeling to create highly specific inhibitors of identified brain isoforms, a novel avenue for drug design using P450 as drug targets may be at hand. This article highlights some notable examples in which the catalytic state of specific P450 isoforms involved in endogenous biochemical reaction pathways are influenced by pharmacological agents. The implications of inhibition of P450-catalzyed oxidation steps that are known or speculated to influence arachadonic acid, cholesterol, and catecholamine neurotransmitters pathways in human brain will be considered.

The effect of tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs) and newer antidepressant drugs on the activity and level of rat CYP3A

The aim of the present study was to investigate the influence of tricyclic antidepressants (TADs: imipramine, amitriptyline, clomipramine, and desipramine), selective serotonin reuptake inhibitors (SSRIs: fluoxetine and sertraline) and novel antidepressant drugs (mirtazapine and nefazodone) on the activity of CYP3A measured as a rate of testosterone 2beta- and 6beta-hydroxylation. The reaction was studied in control liver microsomes in the presence of the antidepressants, as well as in microsomes of rats treated intraperitoneally (i.p.) for 1 day or 2 weeks with pharmacological doses of the drugs (imipramine, amitriptyline, clomipramine, nefazodone 10 mg kg(-1) i.p.; desipramine, fluoxetine, sertraline 5 mg kg(-1) i.p.; mirtazapine 3 mg kg(-1) i.p.), in the absence of the antidepressants in vitro. The investigated antidepressants added to control liver microsomes produced some inhibitory effects on CYP3A activity, which were very weak (most of TADs, K(i)=145-212 microM), modest (clomipramine and sertraline, K(i)=67.5 and 62 microM, respectively) or moderate (nefazodone and fluoxetine, K(i)=42 and 43 microM, respectively). Mirtazapine did not display this kind of properties. One-day exposure of rats to TADs substantially decreased the activity of CYP3A in liver microsomes, which was maintained during chronic treatment. The observed decreases in the enzyme activity were in contrast to the increased CYP3A protein level found after chronic treatment with TADs. On the other hand, sertraline increased the activity of the enzyme after its prolonged administration and its effect correlated positively with the observed elevation in CYP3A protein level. Fluoxetine, mirtazapine and nefazodone did not change the activity of CYP3A in liver microsomes after their administration to rats. Three different mechanisms of the antidepressants-CYP3A interaction are postulated: 1) a direct inhibition of CYP3A by nefazodone, SSRIs and clomipramine, shown in vitro, with the inhibitory effect of nefazodone being the strongest, but weaker than the effects of this drug on human CYP3A4; 2) in vivo inhibition of CYP3A produced by 1 day and maintained during chronic treatment with TADs, which suggests inactivation of the enzyme by reactive metabolites; 3) in vivo induction by sertraline of CYP3A produced only by chronic treatment with the antidepressant, which suggests its influence on the enzyme regulation.

Tolerability and safety of fluvoxamine and other antidepressants

Selective serotonin [5-hydroxytryptamine (5-HT)] reuptake inhibitors (SSRIs) and the 5-HT noradrenaline reuptake inhibitor, venlafaxine, are mainstays in treatment for depression. The highly specific actions of SSRIs of enhancing serotonergic neurotransmission appears to explain their benefit, while lack of direct actions on other neurotransmitter systems is responsible for their superior safety profile compared with tricyclic antidepressants. Although SSRIs (and venlafaxine) have similar adverse effects, certain differences are emerging. Fluvoxamine may have fewer effects on sexual dysfunction and sleep pattern. SSRIs have a cardiovascular safety profile superior to that of tricyclic antidepressants for patients with cardiovascular disease; fluvoxamine is safe in patients with cardiovascular disease and in the elderly. A discontinuation syndrome may develop upon abrupt SSRI cessation. SSRIs are more tolerable than tricyclic antidepressants in overdose, and there is no conclusive evidence to suggest that they are associated with an increased risk of suicide. Although the literature suggests that there are no clinically significant differences in efficacy amongst SSRIs, treatment decisions need to be based on considerations such as patient acceptability, response history and toxicity.

Interactions between Antiepileptic and Antipsychotic Drugs

Antiepileptic and antipsychotic drugs are often prescribed together. Interactions between the drugs may affect both efficacy and toxicity. This is a review of human clinical data on the interactions between the antiepileptic drugs carbamazepine, valproic acid (sodium valproate), vigabatrin, lamotrigine, gabapentin, topiramate, tiagabine, oxcarbazepine, levetiracetam, pregabalin, felbamate, zonisamide, phenobarbital and phenytoin with the antipsychotic drugs risperidone, olanzapine, quetiapine, clozapine, amisulpride, sulpiride, ziprasidone, aripiprazole, haloperidol and chlorpromazine; the limited information on interactions between antiepileptic drugs and zuclopenthixol, periciazine, fluphenazine, flupenthixol and pimozide is also presented. Many of the interactions depend on the induction or inhibition of the cytochrome P450 isoenzymes, but other important mechanisms involve the uridine diphosphate glucuronosyltransferase isoenzymes and protein binding. There is some evidence for the following effects. Carbamazepine decreases the plasma concentrations of both risperidone and its active metabolite. It also decreases concentrations of olanzapine, clozapine, ziprasidone, haloperidol, zuclopenthixol, flupenthixol and probably chlorpromazine and fluphenazine. Quetiapine increases the ratio of carbamazepine epoxide to carbamazepine and this may lead to toxicity. The data on valproic acid are conflicting; it may either increase or decrease clozapine concentrations, and it appears to decrease aripiprazole concentrations. Chlorpromazine possibly increases valproic acid concentrations. Lamotrigine possibly increases clozapine concentrations. Phenobarbital decreases clozapine, haloperidol and chlorpromazine concentrations. Phenytoin decreases quetiapine, clozapine, haloperidol and possibly chlorpromazine concentrations. There are major gaps in the data. In many cases there are no published clinical data on interactions that would be predicted on theoretical grounds.

Clinical efficacy of fluvoxamine and functional polymorphism in a serotonin transporter gene on childhood autism

We studied the correlation between response to fluvoxamine and serotonin transporter gene promoter region polymorphism (5-HTTLPR). Eighteen children with autistic disorder completed a 12-week double-blind, placebo-controlled, randomized crossover study of fluvoxamine. Behavioral assessments were obtained before and at 12 weeks of treatment. 5-HTTLPR (long (l) or short(s)), was analyzed by the PCR method. Ten out of 18 patients responded to fluvoxamine treatment; allele type analysis revealed that clinical global effectiveness was noted significantly more in the l allele than in the s allele. However, with respect to language use, a significant effectiveness was noted in the s allele. 5-HTTLPR may influence the individual responses to fluvoxamine administration.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.