Fluoxetine- and norfluoxetine-mediated complex drug-drug interactions: in vitro to in vivo correlation of effects on CYP2D6, CYP2C19, and CYP3A4

Effects of two commonly used antidepressants amitriptyline and fluoxetine on the pharmacokinetics of abrocitinib in rats

Abrocitinib is approved to treat moderate-to-severe atopic dermatitis and eliminated mainly through cytochrome P450 (CYP450) enzyme. Two commonly used antidepressants, amitriptyline and fluoxetine, could inhibit the activities of CYP2C19 and CYP3A4. In this study, we developed a new and quick ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for quantitatively analyzing the plasma concentration of abrocitinib, and further investigated the effects of amitriptyline or fluoxetine on the pharmacokinetics of abrocitinib in rats. The selectivity, linearity, recovery, accuracy, precision, matrix effect and stability of UPLC-MS/MS assay were satisfied according to the United States Food and Drug Administration (FDA) and European Medicines Agency (EMA) guidelines. Our result showed that when co-administered with amitriptyline and fluoxetine, the CLz/F of abrocitinib was reduced by 44.4 % and 33.3 %, respectively, while the AUC(0-t) of abrocitinib was increased by 77.7 % and 49.4 %, respectively. It indicated that amitriptyline and fluoxetine could significantly increase the plasma concentration of abrocitinib in rats. Thus, dose adjustment of abrocitinib may be required when it is combined with amitriptyline or fluoxetine in ongoing clinical practice.

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialized tools are used. Three tools have been proven useful to personalize drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 50 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimize treatment effects, minimize side effects and ultimately reduce the global burden of diseases, personalized drug treatment has not yet become the standard of care in psychiatry.

Persistence of norfluoxetine in marine mussels

The concentration of pharmaceuticals in coastal waters is tending towards increasing due to a shift of the human population into coastal zones. In parallel, the number of prescriptions of antidepressants, mainly selective serotonin reuptake inhibitors (SSRI), is constantly growing. Most of the SSRI is metabolised into active compounds; for instance, norfluoxetine (NFLU) is the main active metabolite of fluoxetine. In this study, we tested the bioaccumulation and depuration of NFLU in Mytilus trossulus at two environmentally relevant concentrations (100 and 500 ng/L, after six days of exposure and five days of depuration at 10 °C). The concentration of NFLU in the mussels' tissue seems not to be directly proportional to the exposure concentration. The levels of NFLU in the mussels' tissues after the depuration period were comparable to the levels detected at the end of exposure. This indicates that NFLU is not efficiently removed by the mussels and points to a potential risk for consumers of such marine organisms.

Physiologically based pharmacokinetic (PBPK) modeling of the role of CYP2D6 polymorphism for metabolic phenotyping with dextromethorphan

The cytochrome P450 2D6 (CYP2D6) is a key xenobiotic-metabolizing enzyme involved in the clearance of many drugs. Genetic polymorphisms in CYP2D6 contribute to the large inter-individual variability in drug metabolism and could affect metabolic phenotyping of CYP2D6 probe substances such as dextromethorphan (DXM). To study this question, we (i) established an extensive pharmacokinetics dataset for DXM; and (ii) developed and validated a physiologically based pharmacokinetic (PBPK) model of DXM and its metabolites dextrorphan (DXO) and dextrorphan O-glucuronide (DXO-Glu) based on the data. Drug-gene interactions (DGI) were introduced by accounting for changes in CYP2D6 enzyme kinetics depending on activity score (AS), which in combination with AS for individual polymorphisms allowed us to model CYP2D6 gene variants. Variability in CYP3A4 and CYP2D6 activity was modeled based on in vitro data from human liver microsomes. Model predictions are in very good agreement with pharmacokinetics data for CYP2D6 polymorphisms, CYP2D6 activity as described by the AS system, and CYP2D6 metabolic phenotypes (UM, EM, IM, PM). The model was applied to investigate the genotype-phenotype association and the role of CYP2D6 polymorphisms for metabolic phenotyping using the urinary cumulative metabolic ratio (UCMR), DXM/(DXO + DXO-Glu). The effect of parameters on UCMR was studied via sensitivity analysis. Model predictions indicate very good robustness against the intervention protocol (i.e. application form, dosing amount, dissolution rate, and sampling time) and good robustness against physiological variation. The model is capable of estimating the UCMR dispersion within and across populations depending on activity scores. Moreover, the distribution of UCMR and the risk of genotype-phenotype mismatch could be estimated for populations with known CYP2D6 genotype frequencies. The model can be applied for individual prediction of UCMR and metabolic phenotype based on CYP2D6 genotype. Both, model and database are freely available for reuse.

Protective role of ellagic acid and taurine against fluoxetine induced hepatotoxic effects on biochemical and oxidative stress parameters, histopathological changes, and gene expressions of IL-1β, NF-κB, and TNF-α in male Wistar rats

PURPOSES

Hepatic bioactivation of fluoxetine (FXN) could increase free radicals' generation provoking hepatotoxicity. Therefore, the protective effects of ellagic acid (EA) and taurine (TAU) treatments against fluoxetine-induced liver damage in rats were examined.

MATERIALS AND METHODS

Sixty four male Wistar rats were randomly assigned to 8 groups (n = 8). Group (1) Control, group (2) FXN, group (3) FXN + EA, group (4) FXN + TAU, group (5) FXN + EA + TAU, group (6) EA, group (7) TAU, and group (8) EA + TAU. Then, the serum and tissue parameters of the oxidative stress were examined.

KEY FINDINGS

FXN significantly raised serum MDA, protein carbonyl, lipid profile, ALT, AST, ALP, total bilirubin, serum IL-1β; and gene expressions of IL-1β, NF-κB, and TNF-α. Moreover, it significantly decreased HDL-C, ferric reducing antioxidant power (FRAP), catalase activity, vitamin C, and SOD activity in the liver compared to group 1. When compared to group 2, EA and TAU treatment dramatically increased antioxidant capacity and lowered hepatotoxic biochemical markers and cellular inflammation. Results also showed a protective effect of treatment against oxidative damage caused by hepatocytes' cytoarchitecture.

SIGNIFICANCE

Our study concluded the beneficial effects of EA and TAU on FXN-induced hepatotoxicity. These effects were derived from free radical scavenging properties and the anti-inflammatory effects related to IL-1β, NF-κB, and TNF-α gene expression inhibition.

Pregnancy Has No Clinically Significant Effect on the Pharmacokinetics of Bupropion or Its Metabolites

BACKGROUND

Bupropion (BUP) is a chiral antidepressant and smoking cessation aide with benefits and side effects correlated with parent and active metabolite concentrations. BUP is metabolized by CYP2B6, CYP2C19, and CYP3A4 to hydroxy-BUP (OH-BUP) as well as by 11β-hydroxysteroid dehydrogenase-1 and aldo-keto reductases to threohydrobupropion (Threo) and erythrohydrobupropion (Erythro), respectively. As pregnancy alters the activity of drug-metabolizing enzymes, the authors hypothesized that BUP metabolism and BUP metabolite concentrations would be altered during pregnancy, potentially affecting the efficacy and safety of BUP in pregnant women.

METHODS

Pregnant women (n = 8) taking BUP chronically were enrolled, and steady-state plasma samples and dosing interval urine samples were collected during pregnancy and postpartum. Maternal and umbilical cord venous blood samples were collected at delivery from 3 subjects, and cord blood/maternal plasma concentration ratios were calculated. The concentrations of BUP stereoisomers and their metabolites were measured. Paired t tests were used to compare pharmacokinetic parameters during pregnancy and postpartum.

RESULTS

No significant changes were observed in the steady-state plasma concentrations, metabolite to parent ratios, formation clearances, or renal clearance of any of the compounds during pregnancy when compared with postpartum. The umbilical cord venous plasma concentrations of BUP and its metabolites were 30%-60% lower than maternal plasma concentrations.

CONCLUSIONS

This study showed that there are no clinically meaningful differences in the stereoselective disposition of BUP or its metabolites during pregnancy, indicating that dose adjustment during pregnancy may not be necessary. The results also showed that the placenta provides a partial barrier for bupropion and its metabolite distribution to the fetus, with possible placental efflux transport of bupropion and its metabolites.

Factors associated with fluoxetine and norfluoxetine plasma concentrations and clinical response in Mexican patients with mental disorders

Over the last few years, fluoxetine has been one of the most prescribed medications for the treatment of diverse psychiatric conditions in Mexico. Fluoxetine therapeutic effect is consequence of the joint action of the parent drug and its active metabolite, norfluoxetine. However, the clinical efficacy of fluoxetine, can be affected due to diverse factors, such as drug-drug interactions and the large interindividual variability in the pharmacokinetics of this drug. The aim of this study was to determine the factors associated with variability in plasma concentrations of fluoxetine and norfluoxetine and its association with the therapeutic response. Fluoxetine and norfluoxetine plasma concentrations were quantified by liquid chromatography in 81 Mexican patients with mental disorders; 25% of the patients had no medication adherence and 40% were below the reference range of fluoxetine plus norfluoxetine plasma concentrations. The results showed that concentrations can be affected by fluoxetine metabolism caused by CYP2D6 phenotype and the concomitant administration of olanzapine. Furthermore, CYP3A5 and CYP2C19 phenotype were associated with lower anxiety and depression control during treatment with fluoxetine. This study can be a starting point to elucidate the causes of fluoxetine variable response in Mexican patients with mental disorders, as well as to detect and support medication adherence.

Combination Therapy with Fluoxetine and the Nucleoside Analog GS-441524 Exerts Synergistic Antiviral Effects against Different SARS-CoV-2 Variants In Vitro

The ongoing SARS-CoV-2 pandemic requires efficient and safe antiviral treatment strategies. Drug repurposing represents a fast and low-cost approach to the development of new medical treatment options. The direct antiviral agent remdesivir has been reported to exert antiviral activity against SARS-CoV-2. Whereas remdesivir only has a very short half-life time and a bioactivation, which relies on pro-drug activating enzymes, its plasma metabolite GS-441524 can be activated through various kinases including the adenosine kinase (ADK) that is moderately expressed in all tissues. The pharmacokinetics of GS-441524 argue for a suitable antiviral drug that can be given to patients with COVID-19. Here, we analyzed the antiviral property of a combined treatment with the remdesivir metabolite GS-441524 and the antidepressant fluoxetine in a polarized Calu-3 cell culture model against SARS-CoV-2. The combined treatment with GS-441524 and fluoxetine were well-tolerated and displayed synergistic antiviral effects against three circulating SARS-CoV-2 variants in vitro in the commonly used reference models for drug interaction. Thus, combinatory treatment with the virus-targeting GS-441524 and the host-directed drug fluoxetine might offer a suitable therapeutic treatment option for SARS-CoV-2 infections.

High risk of drug toxicity in social isolation stress due to liver dysfunction: Role of oxidative stress and inflammation

BACKGROUND

Previous studies have shown that social isolation stress (SIS) could associate with several systemic diseases; however, the role of SIS on liver dysfunction has yet to be established. This study aimed to investigate the effect of SIS on liver function and possible drug toxicity through liver inflammation and oxidative stress.

METHODS

Male Naval Medical Research Institute mice in two groups of SIS and control were treated with typical anti-depressant and anxiolytic agents including fluoxetine, norfluoxetine, desipramine, and imipramine in both groups. Then blood concentrations (or their active metabolites) of these drugs were assessed. Liver function test, including aspartate transaminase (AST), alanine aminotransferase (ALT), total bilirubin, and conjugated bilirubin), oxidative activity, inflammatory cytokines, and the gene expression of cytochrome P450 enzymes were assessed.

RESULTS

We observed that the liver enzymes including AST and ALT was slightly higher in SIS animals. The blood concentrations of fluoxetine, norfluoxetine, desipramine, and imipramine were significantly higher in SIS animals. The gene expression of CYP1A2, CYP2A6, CYP2C9, CYP2C29, and CYP2D were significantly decreased in SIS animals. Our results showed that SIS animals had significantly higher level of tumor necrosis factor-α, interleukin-1β, and interleukin-6. SIS could significantly decrease the activity of antioxidant agent (Glutathione).

CONCLUSION

We hypothesized that SIS could induce liver dysfunction and decrease the rate of drug clearance through liver inflammation and oxidative stress; therefore, the blood concentration of anti-depressant/anxiolytic agents should closely monitor in SIS due to the high toxicity of these agents.

Prediction of Fluoxetine and Norfluoxetine Pharmacokinetic Profiles Using Physiologically Based Pharmacokinetic Modeling

Fluoxetine is a selective serotonin reuptake inhibitor that is metabolized to norfluoxetine by cytochrome P450 (CYP) 2D6, CYP2C19, and CYP3A4. A physiologically based pharmacokinetic model for fluoxetine and norfluoxetine metabolism was developed to predict and investigate changes in concentration-time profiles according to fluoxetine dosage in the Korean population. The model was developed based on the Certara repository model and information gleaned from the literature. Digitally extracted clinical study data were used to develop and verify the model. Simulations for plasma concentrations of fluoxetine and norfluoxetine after a single dose of 60 or 80 mg fluoxetine were made based on 1000 virtual healthy Korean individuals using the SimCYP version 19 simulator. The mean ratios (simulated/observed) after a single administration of 80 mg fluoxetine for maximum plasma concentration, area under the plasma concentration-time curve, and apparent clearance were 1.12, 1.08, and 0.93 for fluoxetine; the ratios of maximum plasma concentration and area under the plasma concentration-time curve were 1.08 and 1.08, respectively, for norfluoxetine, indicating that the simulated concentration-time profiles of fluoxetine and norfluoxetine fitted the observed profiles well. The developed model was used to predict plasma fluoxetine and norfluoxetine concentration-time profiles after repeated administrations of fluoxetine in Korean volunteers. This physiologically based pharmacokinetic model could provide basic understanding of the pharmacokinetic profiles of fluoxetine and its metabolite under various situations.

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.

Anemarsaponin BII inhibits the activity of CYP3A4, 2D6, and 2E1 with human liver microsomes

CONTEXT

Anemarsaponin BII is one of the most active saponins isolated from Anemarrhena asphodeloides Bunge (Asparagaceae), a commonly used Chinese traditional paediatric medicine.

OBJECTIVE

This study investigates the effects of anemarsaponin BII on the activity of CYP450s to provide more guidance for the clinical use of anemarsaponin BII.

MATERIALS AND METHODS

Using various diagnostic substrates, the effects of a fixed concentration of anemarsaponin BII (100 μM) on the activity of eight main isoforms of CYP450s (CYP1A2, 2A6, 3A4, 2C8, 2C9, 2C19, 2D6 and 2E1) was first studied with pooled human liver microsomes (HLMs). Then, dose-dependent (0, 2.5, 5, 10, 25, 50 and 100 μM anemarsaponin BII) and time-dependent (0, 5, 10, 15 and 30 min) experiments were performed to obtain corresponding kinetic parameters.

RESULTS

Anemarsaponin BII showed significant inhibitory effects on the activity of CYP3A4, 2D6 and 2E1 with the IC₅₀ values of 13.67, 16.26 and 19.72 μM. Anemarsaponin BII acted as a non-competitive inhibitor of CYP3A4 with the K_I value of 6.72 μM and competitive inhibitors of CYP2D6 and 2E1 with the K_I values of 8.26 and 9.82 μM, respectively. Additionally, the inhibition of CYP3A4 was revealed to be time-dependent with the K_I value of 4.88 μM and the K_inact value of 0.053/min.

CONCLUSIONS

The inhibitory effect of anemarsaponin BII on the activity of CYP3A4, 2D6 and 2E1 indicated the potential drug-drug interaction between anemarsaponin BII and drugs metabolized by these CYP450s. Further in vivo experiments are needed to validate the potential drug-drug interactions.

Alginate-based drug oral targeting using bio-micro/nano encapsulation technologies

INTRODUCTION

Oral delivery is the most common administrated drug delivery path. However, oral administration of lipophilic drugs has some limitations: they have poor dose-response due to low and varied dissolution kinetics and oral bioavailability with sub-optimal dissolution within the aqueous gastrointestinal microenvironment. Therefore, there is a need for robust formulating methods that protect the drug until it reaches to its optimum absorption site, allowing its optimum pharmacological effects via increasing its intestinal permeation and bioavailability.

AREA COVERED

Herein, we provide insights on orally administered lipophilic drug delivery systems. The detailed description of the obstacles associated with the oral bioavailability of lipophilic drugs are also discussed. Following this, techniques to overcome these obstacles with much emphasis on optimal safety and efficacy are addressed. Newly designed ionic vibrational jet flow encapsulation technology has enormous growth in lipophilic drug delivery systems, which is discussed thereafter.

EXPERT OPINION

Researchers have shown interest in drug's encapsulation. A combination of drug-bile acid and microencapsulation methods can be one promising strategy to improve the oral delivery of lipophilic drugs. However, the most critical aspect of this approach is the selection of bile acids, polymer, and encapsulation technology.

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.

Midazolam: an essential palliative care drug

Midazolam is a commonly used benzodiazepine in palliative care and is considered one of the four essential drugs needed for the promotion of quality care in dying patients. Acting on the benzodiazepine receptor, it promotes the action of gamma-aminobutyric acid. Gamma-aminobutyric acid action promotes sedative, anxiolytic, and anticonvulsant properties. Midazolam has a faster onset and shorter duration of action than other benzodiazepines such as diazepam and lorazepam lending itself to greater flexibility in dosing than other benzodiazepines. The kidneys excrete midazolam and its active metabolite. Metabolism occurs in the liver by the P450 system. This article examines the pharmacology, pharmacodynamics, and clinical uses of midazolam in palliative care.

Adverse pharmacokinetic interactions between illicit substances and clinical drugs

Adverse pharmacokinetic interactions between illicit substances and clinical drugs are of a significant health concern. Illicit substances are taken by healthy individuals as well as by patients with medical conditions such as mental illnesses, acquired immunodeficiency syndrome, diabetes mellitus and cancer. Many individuals that use illicit substances simultaneously take clinical drugs meant for targeted treatment. This concomitant usage can lead to life-threatening pharmacokinetic interactions between illicit substances and clinical drugs. Optimal levels and activity of drug-metabolizing enzymes and drug-transporters are crucial for metabolism and disposition of illicit substances as well as clinical drugs. However, both illicit substances and clinical drugs can induce changes in the expression and/or activity of drug-metabolizing enzymes and drug-transporters. Consequently, with concomitant usage, illicit substances can adversely influence the therapeutic outcome of coadministered clinical drugs. Likewise, clinical drugs can adversely affect the response of coadministered illicit substances. While the interactions between illicit substances and clinical drugs pose a tremendous health and financial burden, they lack a similar level of attention as drug-drug, food-drug, supplement-drug, herb-drug, disease-drug, or other substance-drug interactions such as alcohol-drug and tobacco-drug interactions. This review highlights the clinical pharmacokinetic interactions between clinical drugs and commonly used illicit substances such as cannabis, cocaine and 3, 4-Methylenedioxymethamphetamine (MDMA). Rigorous efforts are warranted to further understand the underlying mechanisms responsible for these clinical pharmacokinetic interactions. It is also critical to extend the awareness of the life-threatening adverse interactions to both health care professionals and patients.

Adverse Events Associated with Melatonin for the Treatment of Primary or Secondary Sleep Disorders: A Systematic Review

BACKGROUND

Melatonin is widely available either on prescription for the treatment of sleep disorders or as an over-the-counter dietary supplement. Melatonin has also recently been licensed in the UK for the short-term treatment of jetlag. Little is known about the potential for adverse events (AEs), in particular AEs resulting from long-term use. Concern has been raised over the possible risks of exposure in certain populations including pre-adolescent children and patients with epilepsy or asthma.

OBJECTIVES

The aim of this systematic review was to assess the evidence for AEs associated with short-term and longer-term melatonin treatment for sleep disorders.

METHODS

A literature search of the PubMed/Medline database and Google Scholar was conducted to identify randomised, placebo-controlled trials (RCTs) of exogenous melatonin administered for primary or secondary sleep disorders. Studies were included if they reported on both the types and frequencies of AEs. Studies of pre-term infants, studies of < 1 week in duration or involving single doses of melatonin and studies in languages other than English were excluded. Findings from open-label studies that raised concerns relating to AE reports in patients were also examined. Studies were assessed for quality of reporting against the Consolidated Standards of Reporting Trials (CONSORT) checklist and for risk of bias against the Cochrane Collaboration risk-of-bias criteria.

RESULTS

37 RCTs met criteria for inclusion. Daily melatonin doses ranged from 0.15 mg to 12 mg. Subjects were monitored for up to 29 weeks, but most studies were of much shorter duration (4 weeks or less). The most frequently reported AEs were daytime sleepiness (1.66%), headache (0.74%), other sleep-related AEs (0.74%), dizziness (0.74%) and hypothermia (0.62%). Very few AEs considered to be serious or of clinical significance were reported. These included agitation, fatigue, mood swings, nightmares, skin irritation and palpitations. Most AEs either resolved spontaneously within a few days with no adjustment in melatonin, or immediately upon withdrawal of treatment. Melatonin was generally regarded as safe and well tolerated. Many studies predated publication of the CONSORT checklist and consequently did not conform closely to the guidelines. Similarly, only eight studies were judged 'good' overall with respect to the Cochrane risk-of-bias criteria. Of the remaining papers, 16 were considered 'fair' and 13 'poor' but publication of almost half of the papers preceded that of the earliest version of the guidelines.

CONCLUSION

Few, generally mild to moderate, AEs were associated with exogenous melatonin. No AEs that were life threatening or of major clinical significance were identified. The scarcity of evidence from long-term RCTs, however, limits the conclusions regarding the safety of continuous melatonin therapy over extended periods. There are insufficient robust data to allow a meaningful appraisal of concerns that melatonin may result in more clinically significant adverse effects in potentially at-risk populations. Future studies should be designed to comply with appropriate quality standards for RCTs, which most past studies have not.

The Herb-Drug Pharmacokinetic Interaction of Fluoxetine and Its Metabolite Norfluoxetine with a Traditional Chinese Medicine in Rats by LC-MS/MS

Background

Fluoxetine (FLU) is the first-line and widely used medication for depression. The combination of Chaihu Shugan san (CSGS) and FLU is commonly used to enhance antidepressant effects and reduce side effects.

Objective

The primary objective of this study was to investigate the potential pharmacokinetic effect of CSGS on FLU.

Materials and Methods

Thirty-two healthy adult male Sprague-Dawley (SD) rats were randomly divided into four groups, the fluoxetine group and multiple dose groups A, B, and C. The rats in the different groups were orally administered with a combination of FLU and different doses of CSGS for 14 d. On the fifteenth day, serial blood samples were taken from the caudal vein before the administration and at 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 10, 12, 24, 36, and 48 h after the administration. A liquid-liquid extraction method was applied to extract the analytes from serum. Then, the concentrations of FLU and its metabolite, norfluoxetine (NOF), were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pharmacokinetic parameters were calculated by DAS 3.2.8 program and compared by statistic analysis.

Results

Compared with the FLU group, the FLU and NOF area under the plasma concentration-time curve (AUC) (0–∞) in multiple dose group C was significantly increased, while the NOF AUCs (0–∞) in multiple dose group A and multiple dose group B were decreased. Compared with the FLU group, the NOF clearance (CL) in multiple dose group C was decreased, while the CL in multiple dose groups A and B was increased.

Discussion and Conclusion

There were some differences in pharmacokinetic parameters between the FLU group and multiple dose groups, and CSGS can affect the pharmacokinetics of fluoxetine.

Computational and experimental studies on the interaction between butyrylcholinesterase and fluoxetine: implications in health and disease

Butyrylcholinesterase (BChE) is a serine esterase that plays a role in the detoxification of natural as well as synthetic ester-bond-containing compounds. Alterations in BChE activity are associated with a number of diseases. Cholinergic system abnormalities in particular are correlated with the formation of senile plaques in Alzheimer's disease (AD), and administration of cholinesterase inhibitors is a common therapeutic approach used to treat AD. Here, our aim was to study the interaction between BChE and fluoxetine. Molecular docking simulations revealed that fluoxetine penetrated deep into the active-site gorge of BChE and that it was engaged in stabilizing noncovalent interactions with multiple subsites. In substrate kinetic studies, the V_m, K_m, k_cat and k_cat/K_m values were found to be 20.59 ± 0.36 U mg^-1 protein, 194 ± 14 µM, 1.3 × 10⁸ s^-1 and 6.7 × 10⁵ µM^-1s^-1, respectively. Based on inhibitory studies, fluoxetine appeared to inhibit BChE competitively, with an IC₅₀ value of 104 µM and a K_i value of 36.3 ± 4.7 µM. Overall, both the low K_i value and the high number of BChE-fluoxetine interactions suggest that fluoxetine is a potent inhibitor of BChE, although in vivo mechanisms for the direct effects of BChE inhibition on various pathologies remain to be further investigated.

Pharmacokinetics and Transplacental Transfer of Fluoxetine Enantiomers and Their Metabolites in Pregnant Women

Considering that fluoxetine (FLX) is used to treat depressive states during pregnancy and that it is a cytochrome P450 (CYP)2D6 inhibitor, which is involved in the metabolism of both of its enantiomers, this study aims to describe the enantioselective distribution and metabolism of FLX and of its metabolite norfluoxetine (NorFLX) following a single oral dose. Nine healthy pregnant women received 20 mg FLX at 32 weeks of gestation and later at the day of delivery. The apparent clearance of (S)-(+)-FLX (1.45 vs. 0.66 L/hour/kg) and the area under the plasma concentration vs. time curve (AUC) of the (S)-(+)-NorFLX (AUC_0-∞ 942.7 vs. 498.6 ng hour/mL) were higher (P < 0.05) than those of the respective (R)-(-) enantiomers, indicating that the (S)-(+)-FLX enantiomer is preferentially metabolized to (S)-(+)-NorFLX. The placental transfer (umbilical vein/maternal vein) of FLX and NorFLX is low (30-40%), with the predominant transfer of (S)-(+)-FLX (44 vs. 33%). The distribution of the enantiomers of FLX and NorFLX to amniotic fluid is low (< 10%).

Pharmacotherapy Pearls in Rheumatology for the Care of Older Adult Patients: Focus on Oral Disease-Modifying Antirheumatic Drugs and the Newest Small Molecule Inhibitors

Providing safe and effective pharmacotherapy to geriatric patients with rheumatologic disorders is challenging. Multidisciplinary care involving rheumatologists, primary care physicians, and other specialties can optimize benefit and reduce adverse outcomes. Oral disease-modifying antirheumatic drugs, including methotrexate, hydroxychloroquine, sulfasalazine, and leflunomide, and the small molecule inhibitors tofacitinib and apremilast have distinctive monitoring requirements and specific adverse reaction profiles. This article provides clinically relevant pearls for use of these interventions in older patients.

Evaluation of In Vitro Cytochrome P450 Inhibition and In Vitro Fate of Structurally Diverse N-Oxide Metabolites: Case Studies with Clozapine, Levofloxacin, Roflumilast, Voriconazole and Zopiclone

BACKGROUND AND OBJECTIVES

The role of metabolite(s) to elicit potential clinical drug-drug interaction (DDI) via cytochrome P450 enzymes (CYP) is gaining momentum. In this context, the role of N-oxides for in vitro CYP inhibition has not been evaluated. The objectives of this study were: (a) to examine in vitro CYP inhibition of N-oxides of clozapine, levofloxacin, roflumilast, voriconazole and zopiclone in a tiered approach and (b) evaluate in vitro fate of aforementioned N-oxides examined in recombinant CYPs, human microsomes and hepatocytes.

METHODS

CYP enzymes evaluated in the work included: CYP1A2, 2B6, 2C9, 2C19, 2D6 and 3A4 using standard procedures for incubation with appropriate probe substrates. The initial cutoff for CYP inhibition was ≥50% using 2 and 10 µM concentrations of various N-oxide metabolites (Tier 1). IC₅₀ values were constructed for the CYP pathway(s) that showed ≥50% inhibition (Tier 2). In addition, co-incubation of N-oxides with parent was performed to evaluate potentiation of CYP inhibition (Tier 3).

RESULTS

N-oxides of clozapine (CYP2B6/2C19) and voriconazole (CYP2C9/3A4) showed CYP inhibition ≥50%. Clozapine-N-oxide inhibited CYP2B6 and CYP2C19 pathways with IC₅₀ of 8.3 and 8.7 µM, respectively. Voriconazole-N-oxide inhibited CYP2B6 and CYP2C19 pathways with IC₅₀ of 10.5 and 11.2 µM, respectively. Co-incubation of clozapine-N-oxide with clozapine potentiated CYP2B6/2C19 pathways; however, incubation of voriconazole-N-oxide with voriconazole did not appear to potentiate the CYP pathways because parent caused an inhibition of almost 80%. None of the N-oxides appeared to further undergo biotransformation as judged by the in vitro metabolic fate experiments (stage 2).

CONCLUSIONS

Clinical DDI potential of specific CYP enzymes needs to be considered arising due to circulatory concentrations of certain N-oxides depending on the dose size and/or frequency of dosing of the respective parent drugs.

Updating the Evidence of the Interaction Between Clopidogrel and CYP2C19-Inhibiting Selective Serotonin Reuptake Inhibitors: A Cohort Study and Meta-Analysis

INTRODUCTION

We previously found that patients who initiate clopidogrel while treated with a cytochrome P450 (CYP) 2C19-inhibiting selective serotonin reuptake inhibitor (SSRI) have a higher risk of subsequent ischemic events than patients treated with other SSRIs. It is not known whether initiating an inhibiting SSRI while treated with clopidogrel will also increase risk of ischemic events.

OBJECTIVE

The aim of this study was to assess clinical outcomes following initiation of a CYP2C19-inhibiting SSRI versus initiation of other SSRIs among patients treated with clopidogrel and to update existing evidence on the clinical impact of clopidogrel-SSRI interaction.

METHODS

Using five US databases (1998-2013), we conducted a cohort study of clopidogrel initiators who encountered treatment with SSRI during their clopidogrel therapy. Patients were matched by propensity score (PS) and followed for as long as they were exposed to both clopidogrel and index SSRI group. Outcomes were a composite ischemic event (myocardial infarction, ischemic stroke, or a revascularization procedure, whichever came first) and a composite major bleeding event (gastrointestinal bleed or hemorrhagic stroke, whichever came first). Results were combined via random-effects meta-analysis with previous evidence from subjects initiating clopidogrel while on SSRI therapy.

RESULTS

The PS-matched cohort comprised 2346 clopidogrel users starting CYP2C19-inhibiting SSRI therapy and 16,115 starting other SSRIs (mean age 61 years; 59% female). Compared with those treated with a non-inhibiting SSRI, the hazard ratio (HR) for patients treated with a CYP2C19-inhibiting SSRI was 1.07 (95% confidence interval [CI] 0.82-1.40) for the ischemic outcome and 1.00 (95% CI 0.42-2.36) for bleeding. The pooled estimates were 1.11 (95% CI 1.01-1.22) for ischemic events and 0.80 (95% CI 0.55-1.18) for bleeding.

CONCLUSIONS

We observed similar estimates of association between the two studies. The updated evidence still indicates a small decrease in clopidogrel effectiveness associated with concomitant exposure to clopidogrel and CYP2C19-inhibiting SSRIs.

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.

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.

Physiologically Based Pharmacokinetic Model of the CYP2D6 Probe Atomoxetine: Extrapolation to Special Populations and Drug-Drug Interactions

Physiologically based pharmacokinetic (PBPK) modeling of drug disposition and drug-drug interactions (DDIs) has become a key component of drug development. PBPK modeling has also been considered as an approach to predict drug disposition in special populations. However, whether models developed and validated in healthy populations can be extrapolated to special populations is not well established. The goal of this study was to determine whether a drug-specific PBPK model validated using healthy populations could be used to predict drug disposition in specific populations and in organ impairment patients. A full PBPK model of atomoxetine was developed using a training set of pharmacokinetic (PK) data from CYP2D6 genotyped individuals. The model was validated using drug-specific acceptance criteria and a test set of 14 healthy subject PK studies. Population PBPK models were then challenged by simulating the effects of ethnicity, DDIs, pediatrics, and renal and hepatic impairment on atomoxetine PK. Atomoxetine disposition was successfully predicted in 100% of healthy subject studies, 88% of studies in Asians, 79% of DDI studies, and 100% of pediatric studies. However, the atomoxetine area under the plasma concentration versus time curve (AUC) was overpredicted by 3- to 4-fold in end stage renal disease and hepatic impairment. The results show that validated PBPK models can be extrapolated to different ethnicities, DDIs, and pediatrics but not to renal and hepatic impairment patients, likely due to incomplete understanding of the physiologic changes in these conditions. These results show that systematic modeling efforts can be used to further refine population models to improve the predictive value in this area.

A strategy for early-risk predictions of clinical drug-drug interactions involving the GastroPlusTM DDI module for time-dependent CYP inhibitors

1. A set of reference compounds for time-dependent inhibition (TDI) of cytochrome P450 with available literature data for k_inact and K_I was used to predict clinical implications using the GastroPlus^TM software. Comparisons were made to in vivo literature interaction data. 2. The predicted AUC ratios (AUC_+inhibitor/AUC_control) could be compared with the observed ratios from literature for all compounds with detailed information about in vivo administration, pharmacokinetics and in vivo interactions (N = 21). For this dataset, the difference between predicted and observed AUC ratios for interactions with midazolam was within twofold for all compounds except one (telaprevir, for which non-CYP-mediated metabolism likely plays a role after multiple dosing). 3. The sensitivity, specificity and accuracy of the GastroPlus^TM predictions using a binary classification as no-to-weak interaction versus moderate-to-strong interaction for all compounds with available in vivo interaction data, were 80%, 82% and 81%, respectively (N = 31). 4. As a result of our evaluations of the DDI module in GastroPlus^TM, we have implemented an early TDI risk assessment decision tree for our drug discovery projects involving in vitro screening and early GastroPlus^TM predictions. Shifted IC₅₀ values are determined and k_inact/K_I estimated (by using a regression line established with in house-shifted IC₅₀ values and literature k_inact/K_I ratios), followed by GastroPlus^TM predictions.

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

Aims

Pridopidine is an oral drug in clinical development for treatment of patients with Huntington's disease. This study examined the interactions of pridopidine with in vitro cytochrome P450 activity and characterized the effects of pridopidine on CYP2D6 activity in healthy volunteers using metoprolol as a probe substrate. The effect of food on pridopidine exposure was assessed.

Methods

The ability of pridopidine to inhibit and/or induce in vitro activity of drug metabolizing enzymes was examined in human liver microsomes and fresh hepatocytes. CYP2D6 inhibition potency and reversibility was assessed using dextromethorphan. For the clinical assessment, 22 healthy subjects were given metoprolol 100 mg alone and concomitantly with steady‐state pridopidine 45 mg twice daily. Food effect on a single 90 mg dose of pridopidine was evaluated in a crossover manner. Safety assessments and pharmacokinetic sampling occurred throughout the study.

Results

Pridopidine was found to be a metabolism dependent inhibitor of CYP2D6, the main enzyme catalysing its own metabolism. Flavin‐containing monooxygenase heat inactivation of liver microsomes did not affect pridopidine metabolism‐dependent inhibition of CYP2D6 and its inhibition of CYP2D6 was not reversible with addition of FeCN₃. Exposure to metoprolol was markedly increased when coadministered with pridopidine; the ratio of the geometric means (90% confidence interval) for maximum observed plasma concentration, and area under the plasma concentration–time curve from time 0 to the time of the last quantifiable concentration and extrapolated to infinity were 3.5 (2.9, 4.22), 6.64 (5.27, 8.38) and 6.55 (5.18, 8.28), respectively. Systemic exposure to pridopidine was unaffected by food conditions.

Conclusions

As pridopidine is a metabolism‐dependent inhibitor of CYP2D6, systemic levels of drugs metabolized by CYP2D6 may increase with chronic coadministration of pridopidine. Pridopidine can be administered without regard to food.

Simultaneous administration of fluoxetine and simvastatin ameliorates lipid profile, improves brain level of neurotransmitters, and increases bioavailability of simvastatin

Simvastatin (STT), a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, is widely prescribed for dyslipidemia, whereas fluoxetine (FLX) is the first-choice drug for the treatment of depression and anxiety. A recent report suggests that selective serotonin reuptake inhibitors can interact with the cytochrome P450 3A4 substrate, and another one suggests that STT enhances the antidepressant activity of FLX. However, the data are inconclusive. The present study was designed to explore the pharmacokinetic and pharmacodynamic consequences of coadministration of STT and FLX in experimental animals. For this, Wistar rats weighing 250±10 g were divided into four groups, including control, STT (40 mg/kg/day), FLX (20 mg/kg/day), and STT+FLX group, respectively. After the dosing period of 4 weeks, the animals were sacrificed, and the blood and brain samples were collected for the analysis of STT, simvastatin acid (STA), FLX, total cholesterol, triglyceride, high-density lipoprotein (HDL), 5-hydroxytryptamine, dopamine, and hydroxy indole acetic acid. It was found that the coadministration resulted in a significant increase in the bioavailability of STT in the plasma (41.8%) and brain (68.7%) compared to administration of STT alone (p<0.05). The maximum drug concentration (C_max) of STT was also found to be increased significantly in the plasma and brain compared to that achieved after monotherapy (p<0.05). However, STT failed to improve the pharmacokinetics of FLX up to a significant level. The results of this study showed that the combined regimen significantly reduced the level of cholesterol and triglyceride and increased the level of HDL when compared to STT monotherapy. Furthermore, the coadministration of STT with FLX led to an elevated level of neurotransmitters in the brain (p<0.05). FLX increased the concentration of STT in the plasma and brain. The coadministration of these drugs also led to an improved lipid profile. However, in the long-term, this interaction may have a vital clinical importance because the increase in STT level may lead to life-threatening side effects associated with statins.

Impact of an Interaction Between Clopidogrel and Selective Serotonin Reuptake Inhibitors

Clopidogrel is a pro-drug that requires activation by the cytochrome P450 (CYP) enzyme system. Patients receiving clopidogrel are often treated with selective serotonin reuptake inhibitors (SSRIs) for co-existing depression. SSRIs that inhibit the CYP2C19 enzyme have the potential to reduce the effectiveness of clopidogrel. Using 5 US databases (1998 to 2013), we conducted a cohort study of adults who initiated clopidogrel while being treated with either an SSRI that inhibits CYP2C19 (fluoxetine and fluvoxamine) or a noninhibiting SSRI. Patients were matched by propensity score and followed for as long as they were exposed to both clopidogrel and the index SSRI group (primary analysis) or for 180 days after clopidogrel initiation (sensitivity analysis). Outcomes included a composite ischemic event (myocardial infarction, ischemic stroke, or a revascularization procedure) and a composite major bleeding event (gastrointestinal bleed or hemorrhagic stroke). The final propensity score-matched cohort comprised 9,281 clopidogrel initiators on CYP2C19-inhibiting SSRIs and 44,278 clopidogrel initiators on a noninhibiting SSRIs. Compared with those treated with a noninhibiting SSRI, patients on a CYP2C19-inhibiting SSRI had an increased risk of ischemic events (hazard ratio [HR] 1.12; 95% confidence interval [CI] 1.01 to 1.24), which was more pronounced in patients ≥65 years (HR 1.22; 95% CI 1.00 to 1.48). The HR for major bleeding was 0.76 (95% CI 0.50 to 1.17). In conclusion, the findings from this large, population-based study suggest that being treated with a CYP2C19-inhibiting SSRI when initiating clopidogrel may be associated with slight decrease in effectiveness of clopidogrel.

Impact of Drug Treatment at Neonatal Ages on Variability of Drug Metabolism and Drug-drug Interactions in Adult Life

PURPOSE OF REVIEW

As the number of patients taking more than one medication concurrently continues to increase, predicting and preventing drug-drug interactions (DDIs) is now more important than ever. Administration of one drug can cause changes in the expression and activity of drug metabolizing enzymes (DMEs) and alter the efficacy or toxicity of other medications that are substrates for these enzymes, resulting in a DDI. In today's medical practice, potential DDIs are evaluated based on the current medications a patient is taking with little regard to drugs the patient has been exposed to in the past. The purpose of this review is to discuss potential impacts of drug treatment at neonatal ages on the variability of drug metabolism and DDIs in adult life.

RECENT FINDINGS

Existing evidence from the last thirty years has shown that exposure to certain xenobiotics during neonatal life has the potential to persistently alter DME expression through adult life. With recent advancements in the understanding of epigenetic regulation on gene expression, this phenomenon is resurfacing in the scientific community in hopes of defining possible mechanisms. Exposure to compounds that have the ability to bind nuclear receptors and trigger epigenetic modifications at neonatal and pediatric ages may have long-term, if not permanent, consequences on gene expression and DME activity.

SUMMARY

The information summarized in this review should challenge the way current healthcare providers assess DDI potential and may offer an explanation to the significant interindividual variability in drug metabolism that is observed among patients.

Use of Human Plasma Samples to Identify Circulating Drug Metabolites that Inhibit Cytochrome P450 Enzymes

Drug interactions elicited through inhibition of cytochrome P450 (P450) enzymes are important in pharmacotherapy. Recently, greater attention has been focused on not only parent drugs inhibiting P450 enzymes but also on possible inhibition of these enzymes by circulating metabolites. In this report, an ex vivo method whereby the potential for circulating metabolites to be inhibitors of P450 enzymes is described. To test this method, seven drugs and their known plasma metabolites were added to control human plasma at concentrations previously reported to occur in humans after administration of the parent drug. A volume of plasma for each drug based on the known inhibitory potency and time-averaged concentration of the parent drug was extracted and fractionated by high-pressure liquid chromatography-mass spectrometry, and the fractions were tested for inhibition of six human P450 enzyme activities (CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4). Observation of inhibition in fractions that correspond to the retention times of metabolites indicates that the metabolite has the potential to contribute to P450 inhibition in vivo. Using this approach, norfluoxetine, hydroxyitraconazole, desmethyldiltiazem, desacetyldiltiazem, desethylamiodarone, hydroxybupropion, erythro-dihydrobupropion, and threo-dihydrobupropion were identified as circulating metabolites that inhibit P450 activities at a similar or greater extent as the parent drug. A decision tree is presented outlining how this method can be used to determine when a deeper investigation of the P450 inhibition properties of a drug metabolite is warranted.

An ex Vivo Model for Evaluating Blood-Brain Barrier Permeability, Efflux, and Drug Metabolism

The metabolism of drugs in the brain is difficult to study in most species because of enzymatic instability in vitro and interference from peripheral metabolism in vivo. A locust ex vivo model that combines brain barrier penetration, efflux, metabolism, and analysis of the unbound fraction in intact brains was evaluated using known drugs. Clozapine was analyzed, and its major metabolites, clozapine N-oxide (CNO) and N-desmethylclozapine (NDMC), were identified and quantified. The back-transformation of CNO into clozapine observed in humans was also observed in locusts. In addition, risperidone, citalopram, fluoxetine, and haloperidol were studied, and one preselected metabolite for each drug was analyzed, identified, and quantified. Metabolite identification studies of clozapine and midazolam showed that the locust brain was highly metabolically active, and 18 and 14 metabolites, respectively, were identified. The unbound drug fraction of clozapine, NDMC, carbamazepine, and risperidone was analyzed. In addition, coadministration of drugs with verapamil or fluvoxamine was performed to evaluate drug-drug interactions in all setups. All findings correlated well with the data in the literature for mammals except for the stated fact that CNO is a highly blood-brain barrier permeant compound. Overall, the experiments indicated that invertebrates might be useful for screening of blood-brain barrier permeation, efflux, metabolism, and analysis of the unbound fraction of drugs in the brain in early drug discovery.

Development and Characterization of Novel and Selective Inhibitors of Cytochrome P450 CYP26A1, the Human Liver Retinoic Acid Hydroxylase

Cytochrome P450 CYP26 enzymes are responsible for all-trans-retinoic acid (atRA) clearance. Inhibition of CYP26 enzymes will increase endogenous atRA concentrations and is an attractive therapeutic target. However, the selectivity and potency of the existing atRA metabolism inhibitors toward CYP26A1 and CYP26B1 is unknown, and no selective CYP26A1 or CYP26B1 inhibitors have been developed. Here the synthesis and potent inhibitory activity of the first CYP26A1 selective inhibitors is reported. A series of nonazole CYP26A1 selective inhibitors was identified with low nM potency. The lead compound 3-{4-[2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)-1,3-dioxolan-2-yl] phenyl}4-propanoic acid (24) had 43-fold selectivity toward CYP26A1 with an IC50 of 340 nM. Compound 24 and its two structural analogues also inhibited atRA metabolism in HepG2 cells, resulting in increased potency of atRA toward RAR activation. The identified compounds have potential to become novel treatments aiming to elevate endogenous atRA concentrations and may be useful as cotreatment with atRA to combat therapy resistance.

Physiologically Based Pharmacokinetic (PBPK) Modeling and Simulation Approaches: A Systematic Review of Published Models, Applications, and Model Verification

Modeling and simulation of drug disposition has emerged as an important tool in drug development, clinical study design and regulatory review, and the number of physiologically based pharmacokinetic (PBPK) modeling related publications and regulatory submissions have risen dramatically in recent years. However, the extent of use of PBPK modeling by researchers, and the public availability of models has not been systematically evaluated. This review evaluates PBPK-related publications to 1) identify the common applications of PBPK modeling; 2) determine ways in which models are developed; 3) establish how model quality is assessed; and 4) provide a list of publically available PBPK models for sensitive P450 and transporter substrates as well as selective inhibitors and inducers. PubMed searches were conducted using the terms "PBPK" and "physiologically based pharmacokinetic model" to collect published models. Only papers on PBPK modeling of pharmaceutical agents in humans published in English between 2008 and May 2015 were reviewed. A total of 366 PBPK-related articles met the search criteria, with the number of articles published per year rising steadily. Published models were most commonly used for drug-drug interaction predictions (28%), followed by interindividual variability and general clinical pharmacokinetic predictions (23%), formulation or absorption modeling (12%), and predicting age-related changes in pharmacokinetics and disposition (10%). In total, 106 models of sensitive substrates, inhibitors, and inducers were identified. An in-depth analysis of the model development and verification revealed a lack of consistency in model development and quality assessment practices, demonstrating a need for development of best-practice guidelines.

Physiologically based pharmacokinetic modeling to predict complex drug-drug interactions: a case study of AZD2327 and its metabolite, competitive and time-dependent CYP3A inhibitors

4-{(R)-(3-Aminophenyl)[4-(4-fluorobenzyl)-piperazin-1-yl]methyl}-N,N-diethylbenzamide (AZD2327) is a highly potent and selective agonist of the δ-opioid receptor. AZD2327 and N-deethylated AZD2327 (M1) are substrates of cytochrome P450 3A (CYP3A4) and comprise a complex multiple inhibitory system that causes competitive and time-dependent inhibition of CYP3A4. The aim of the current work was to develop a physiologically based pharmacokinetic (PBPK) model to predict quantitatively the magnitude of CYP3A4 mediated drug-drug interaction with midazolam as the substrate. Integrating in silico, in vitro and in vivo PK data, a PBPK model was successfully developed to simulate the clinical accumulation of AZD2327 and its primary metabolite. The inhibition of CYP3A4 by AZD2327, using midazolam as a probe drug, was reasonably predicted. The predicted maximum concentration (Cmax) and area under the concentration-time curve (AUC) for midazolam were increased by 1.75 and 2.45-fold, respectively, after multiple dosing of AZD2327, indicating no or low risk for clinically relevant drug-drug interactions (DDI). These results are in agreement with those obtained in a clinical trial with a 1.4 and 1.5-fold increase in Cmax and AUC of midazolam, respectively. In conclusion, this model simulated DDI with less than a two-fold error, indicating that complex clinical DDI associated with multiple mechanisms, pathways and inhibitors (parent and metabolite) can be predicted using a well-developed PBPK model.

Quantitative Rationalization of Gemfibrozil Drug Interactions: Consideration of Transporters-Enzyme Interplay and the Role of Circulating Metabolite Gemfibrozil 1-O-β-Glucuronide

Gemfibrozil has been suggested as a sensitive cytochrome P450 2C8 (CYP2C8) inhibitor for clinical investigation by the U.S. Food and Drug Administration and the European Medicines Agency. However, gemfibrozil drug-drug interactions (DDIs) are complex; its major circulating metabolite, gemfibrozil 1-O-β-glucuronide (Gem-Glu), exhibits time-dependent inhibition of CYP2C8, and both parent and metabolite also behave as moderate inhibitors of organic anion transporting polypeptide 1B1 (OATP1B1) in vitro. Additionally, parent and metabolite also inhibit renal transport mediated by OAT3. Here, in vitro inhibition data for gemfibrozil and Gem-Glu were used to assess their impact on the pharmacokinetics of several victim drugs (including rosiglitazone, pioglitazone, cerivastatin, and repaglinide) by employing both static mechanistic and dynamic physiologically based pharmacokinetic (PBPK) models. Of the 48 cases evaluated using the static models, about 75% and 98% of the DDIs were predicted within 1.5- and 2-fold of the observed values, respectively, when incorporating the interaction potential of both gemfibrozil and its 1-O-β-glucuronide. Moreover, the PBPK model was able to recover the plasma profiles of rosiglitazone, pioglitazone, cerivastatin, and repaglinide under control and gemfibrozil treatment conditions. Analyses suggest that Gem-Glu is the major contributor to the DDIs, and its exposure needed to bring about complete inactivation of CYP2C8 is only a fraction of that achieved in the clinic after a therapeutic gemfibrozil dose. Overall, the complex interactions of gemfibrozil can be quantitatively rationalized, and the learnings from this analysis can be applied in support of future predictions of gemfibrozil DDIs.

Prolonged neuropsychiatric effects following management of chloroquine intoxication with psychotropic polypharmacy

Susceptibility to quinoline antimalarial intoxication may reflect individual genetic and drug-induced variation in neuropharmacokinetics. In this report, we describe a case of chloroquine intoxication that appeared to be prolonged by subsequent use of multiple psychotropic medications. This case highlights important new considerations for the management of quinoline antimalarial intoxication.

[Carbamazepine and psychotropic treatment interaction: Two case studies of carbamazepine overdosage]

Drug interaction is a frequent situation in pediatrics and child psychiatry. Carbamazepine (CBZ) is an antiepileptic drug used as a mood stabilizer in child psychiatry. CBZ is known to be a potent inducer of various CYP isoenzymes of cytochrome P450, which might result in a decrease in the plasma concentration of associated treatments. We describe two cases of CBZ overdosage in adolescent inpatients (14 and 16 years). The patients were treated with risperidone associated with fluoxetine in one and with loxapine in the other case, and CBZ was introduced as a mood stabilizer. Patients presented typical clinical symptoms (fatigue, dizziness, gastrointestinal signs, blurred vision). Overdosage was confirmed by an elevated CBZ plasma concentration (17 and 15.5 mg/L, therapeutic range 4-12 mg/L). We recommend introducing CBZ very progressively in patients treated with psychotropics, particularly when it is associated to several treatments. An intensification of clinical and biological follow-up with early plasma concentration testing should allow for better treatment adjustment.