Pharmacokinetic/pharmacodynamic modelling of venlafaxine: pupillary light reflex as a test system for noradrenergic effects

CYP2D6 Phenotype Influences Pharmacokinetic Parameters of Venlafaxine: Results from a Population Pharmacokinetic Model in Older Adults with Depression

In this study, we aimed to improve upon a published population pharmacokinetic (PK) model for venlafaxine (VEN) in the treatment of depression in older adults, then investigate whether CYP2D6 metabolizer status affected model-estimated PK parameters of VEN and its active metabolite O-desmethylvenlafaxine. The model included 325 participants from a clinical trial in which older adults with depression were treated with open-label VEN (maximum 300 mg/day) for 12 weeks and plasma levels of VEN and O-desmethylvenlafaxine were assessed at weeks 4 and 12. We fitted a nonlinear mixed-effect PK model using NONMEM to estimate PK parameters for VEN and O-desmethylvenlafaxine adjusted for CYP2D6 metabolizer status and age. At both lower doses (up to 150 mg/day) and higher doses (up to 300 mg/day), CYP2D6 metabolizers impacted PK model-estimated VEN clearance, VEN exposure, and active moiety (VEN + O-desmethylvenlafaxine) exposure. Specifically, compared with CYP2D6 normal metabolizers, (i) CYP2D6 ultra-rapid metabolizers had higher VEN clearance; (ii) CYP2D6 intermediate metabolizers had lower VEN clearance; (iii) CYP2D6 poor metabolizers had lower VEN clearance, higher VEN exposure, and higher active moiety exposure. Overall, our study showed that including a pharmacogenetic factor in a population PK model could increase model fit, and this improved model demonstrated how CYP2D6 metabolizer status affected VEN-related PK parameters, highlighting the importance of genetic factors in personalized medicine.

Heart Rate Variability: A Measure of Cardiovascular Health and Possible Therapeutic Target in Dysautonomic Mental and Neurological Disorders

Mental illness such as depression and anxiety as well as cerebrovascular disease are linked to impairment of neurocardiac function mediated by changes to the autonomic nervous system with increased sympathetic and decreased parasympathetic activity. Autonomic neurocardiac function can be evaluated by computing heart rate variability (HRV). Over the past decades, research has demonstrated the diagnostic value of HRV as independent predictor of cardiovascular mortality and as disease marker in progressive autonomic nervous system disorders such as Parkinson’s disease. Here we summarize our studies on HRV and its therapeutic modulation in the context of psychopharmacology as well as psychiatric and neurological disorders to honor the life of Professor Evgeny Vaschillo, the true pioneer of HRV research who sadly passed away on November 21st, 2020.

Semimechanistic models to relate noxious stimulation, movement, and pupillary dilation responses in the presence of opioids

Intraoperative targeting of the analgesic effect still lacks an optimal solution. Opioids are currently the main drug used to achieve antinociception, and although underdosing can lead to an increased stress response, overdose can also lead to undesirable adverse effects. To better understand how to achieve the optimal analgesic effect of opioids, we studied the influence of remifentanil on the pupillary reflex dilation (PRD) and its relationship with the reflex movement response to a standardized noxious stimulus. The main objective was to generate population pharmacodynamic models relating remifentanil predicted concentrations to movement and to pupillary dilation during general anesthesia. A total of 78 patients undergoing gynecological surgery under general anesthesia were recruited for the study. PRD and movement response to a tetanic stimulus were measured multiple times before and after surgery. We used nonlinear mixed effects modeling to generate a population pharmacodynamic model to describe both the time profiles of PRD and movement responses to noxious stimulation. Our model demonstrated that movement and PRD are equally depressed by remifentanil. Using the developed model, we changed the intensity of stimulation and simulated remifentanil predicted concentrations maximizing the probability of absence of movement response. An estimated effect site concentration of 2 ng/ml of remifentanil was found to inhibit movement to a tetanic stimulation with a probability of 81%.

Simultaneous Semi-Mechanistic Population Pharmacokinetic Modeling Analysis of Enalapril and Enalaprilat Serum and Urine Concentrations From Child Appropriate Orodispersible Minitablets

Enalapril is recommended as the first line of therapy and is proven to improve survival rates for treatment of Pediatric Heart Failure; however, an approved drug and child appropriate dosage formulation is still absent. The present analysis was conducted to perform a detailed model informed population pharmacokinetic analysis of prodrug enalapril and its active metabolite enalaprilat in serum and urine. Further, a model informed dosage form population-pharmacokinetic analysis was conducted to evaluate differences in pharmacokinetics of enalapril and its active metabolite enalaprilat when prodrug was administered to 24 healthy adults in a crossover, two periods, two treatments, phase I clinical trial using child-appropriate orodispersible mini-tablets (ODMT) and reference (Renitec®) dosage formulation. A simultaneous semi-mechanistic population-pharmacokinetic model was developed using NONMEM software, which predicted full profile serum and urine concentrations of enalapril and enalaprilat. First-order conditional estimation with interaction was used for parameter estimation. Transit compartments added using Erlang distribution method to predicted enalapril absorption and enalaprilat formation phases. Normalized body weight was identified as covariate related to enalapril volume of distribution. Visual predictive check (VPC) plots and conducted bootstrap analysis validated the model. The data from the two formulations were pooled for population-pharmacokinetic analysis and covariate effect of the formulation was found on mean transit time (MTT1) of enalapril absorption. In addition, data of each formulation were modeled separately and the estimated parameters of each individual administered both formulations were correlated using paired samples Wilcoxon rank test (p < 0.05 = significant) which also showed only a significant difference (p = 0.03) in MTT1 i.e., 5 min early appearance of enalapril from ODMT compared to reference tablets. No difference in the pharmacokinetics of active enalaprilat was found from the ODMT compared to the reference formulation. The population pharmacokinetic analysis provided detailed information about the pharmacokinetics of enalapril and enalaprilat, which showed that the ODMT formulation might have similar pharmacodynamic response compared to the reference formulation.

Adverse Effects of Antidepressants for Chronic Pain: A Systematic Review and Meta-analysis

Background

Antidepressants are widely used in the treatment of chronic pain. Applied doses are lower than those needed to unfold an antidepressive effect. While efficacy of antidepressants for chronic pain has been reported in large randomized-controlled trials (RCT), there is inconsistent data on adverse effects and tolerability. We aimed at synthesizing data from RCT to explore adverse effect profiles and tolerability of antidepressants for treatment of chronic pain.

Methods

Systematic literature research and meta-analyses were performed regarding side effects and safety of different antidepressants in the treatment of chronic pain according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The National Center for Biotechnology Information library and MEDLINE were searched. Randomized placebo-controlled trials were included in quantitative data synthesis.

Results

Out of 1,975 screened articles, 33 papers published between 1995 and 2015 were included in our review and 23 studies were included in the meta-analyses. A higher risk for adverse effects compared to placebo was observed in all antidepressants included in our analyses, except nortriptyline. The most prevalent adverse effects were dry mouth, dizziness, nausea, headache, and constipation. Amitriptyline, mirtazapine, desipramine, venlafaxine, fluoxetine, and nortriptyline showed the highest placebo effect-adjusted risk of adverse effects. Risk for withdrawal due to adverse effects was highest in desipramine (risk ratio: 4.09, 95%-confidence interval [1.31; 12.82]) followed by milnacipran, venlafaxine, and duloxetine. The most common adverse effects under treatment with antidepressants were dry mouth, dizziness, nausea, headache, and constipation followed by palpitations, sweating, and drowsiness. However, overall tolerability was high. Each antidepressant showed distinct risk profiles of adverse effects.

Conclusion

Our synthesized data analysis confirmed overall tolerability of low-dose antidepressants for the treatment of chronic pain and revealed drug specific risk profiles. This encompassing characterization of adverse effect profiles might be useful in defining multimodal treatment regimens for chronic pain which also consider patients’ comorbidities and co-medication.

Population pharmacokinetic/pharmacodynamic modelling of the effects of axomadol and its O-demethyl metabolite on pupil diameter and nociception in healthy subjects

AIM

The aim of the present study was to characterize the pharmacokinetic/pharmacodynamic (PK/PD) properties of the active components of axomadol and to quantify their contribution to observed the pupillometric and analgesic (measured through the cold pressor test) effects linking the PD engagement biomarker with clinical response.

METHODS

Healthy subjects (n = 74) received either placebo or axomadol orally at doses ranging from 66 mg to 225 mg following multiple dosing regimens in two separate clinical trials. Plasma concentrations of the two enantiomers of axomadol and their metabolites, and PD responses were measured at specific times. The population analysis was performed using NONMEM 7.2.

RESULTS

The kinetics of the parent drug and its metabolite could be described simultaneously using an extra compartment mimicking the liver, where the metabolite is formed. The SS parent compound elicited a plasma concentration-dependent increase in pupil diameter, with estimates (percentage relative standard errors) of maximal effect (Emax ) and plasma concentration exerting a half-maximal effect (C50 ) of 0.79 (17.4) mm, and 90.7 (27) ng ml(-1) , respectively. The predicted effect site concentrations of the RR O-demethyl metabolite decreased the pupil diameter linearly, with an estimate of the slope of 0.00967 (18.7) mm·ml ng(-1) . An additive model, integrating the net effect on pupil diameter, described adequately the reduction in pain with a linear function. The PK/PD model revealed that each 0.5 mm change in pupil diameter is associated with a 10% decrease in cold pressor area under the concentration-time curve effects.

CONCLUSIONS

The PK/PD analysis performed enabled the individual contributions of the active compounds to the observed effects to be identified and quantified. These effects were in accordance with the known mechanisms of action - namely, opioid agonism and noradrenaline reuptake inhibition.

Pupil function as an indicator of being under the influence of central nervous system-acting substances from a traffic-medicine perspective - Part II

In order to evaluate driving abilities of each traffic participant, standardised and objective measurement methods are needed. The applicability and value of infrared pupillography as an objective measurement method to indicate possible influence of central nervous acting substances has been demonstrated in former publications. Healthy test subjects (n = 41), as well as persons who were under the influence of drugs and/or medication (n = 105), were exposed to different light stimuli using infrared technology in order to demonstrate the relevance of specific parameters of the pupillary light reflex (PLR) in the field of traffic medicine. Based on former reported results, the statistical examination was extended to further parameters of the PLR, which again confirmed the high value of infrared pupillography as a reliable indicator of previous consumption of drugs and/or medication.

Coadministration of tramadol with aripiprazole and venlafaxine--The effect on spatial memory functions in male rats

BACKGROUND

The impairment of memory functions is very common in patients with chronic pain, particularly in patients with existing cognitive disorders. Results of some studies confirmed that tramadol (TRM), a frequently prescribed analgesic drug, improves memory functions in humans. However, there are no studies on the effect of co-administration of TRM with antidepressants or antipsychotics on memory; therefore, the aim of this study was to evaluate the effect of concomitant use of TRM with a second generation antipsychotic-aripiprazole (ARI) and an antidepressant-venlafaxine (VEN) on memory using an animal model.

METHODS

The effect of TRM (5mg/kg)+ARI (1.5mg/kg) and TRM (5mg/kg)+VEN (20mg/kg) on memory in Wistar rats was examined using the Morris water maze test after single and chronic administration (7 and 14 days).

RESULTS

It was observed that a single and chronic administration of TRM, VEN or ARI alone, but not a combination of TRM+VEN or TRM+ARI (except for 14 days of treatment) can improve memory in rats compared to the control group. After 14 days of administration, both combinations achieved improvement similar to each drug individually and improved spatial memory in rats compared to the control animals.

CONCLUSION

It can be assumed that chronic treatment with combinations of TRM+VEN or TRM+ARI is unlikely to cause memory impairment and interfere with either any antidepressant effect of VEN or any antipsychotic effect of ARI in patients suffering from chronic pain using TRM.

Autonomic Dysregulation in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, progressive central neurological disease characterized by inflammation and demyelination. In patients with MS, dysregulation of the autonomic nervous system may present with various clinical symptoms including sweating abnormalities, urinary dysfunction, orthostatic dysregulation, gastrointestinal symptoms, and sexual dysfunction. These autonomic disturbances reduce the quality of life of affected patients and constitute a clinical challenge to the physician due to variability of clinical presentation and inconsistent data on diagnosis and treatment. Early diagnosis and initiation of individualized interdisciplinary and multimodal strategies is beneficial in the management of autonomic dysfunction in MS. This review summarizes the current literature on the most prevalent aspects of autonomic dysfunction in MS and provides reference to underlying pathophysiological mechanisms as well as means of diagnosis and treatment.

Fundamentals of population pharmacokinetic modelling: validation methods

Population pharmacokinetic modelling is widely used within the field of clinical pharmacology as it helps to define the sources and correlates of pharmacokinetic variability in target patient populations and their impact upon drug disposition; and population pharmacokinetic modelling provides an estimation of drug pharmacokinetic parameters. This method's defined outcome aims to understand how participants in population pharmacokinetic studies are representative of the population as opposed to the healthy volunteers or highly selected patients in traditional pharmacokinetic studies. This review focuses on the fundamentals of population pharmacokinetic modelling and how the results are evaluated and validated. This review defines the common aspects of population pharmacokinetic modelling through a discussion of the literature describing the techniques and placing them in the appropriate context. The concept of validation, as applied to population pharmacokinetic models, is explored focusing on the lack of consensus regarding both terminology and the concept of validation itself. Population pharmacokinetic modelling is a powerful approach where pharmacokinetic variability can be identified in a target patient population receiving a pharmacological agent. Given the lack of consensus on the best approaches in model building and validation, sound fundamentals are required to ensure the selected methodology is suitable for the particular data type and/or patient population. There is a need to further standardize and establish the best approaches in modelling so that any model created can be systematically evaluated and the results relied upon.

Criteria for evaluation of disease extent by (123)I-metaiodobenzylguanidine scans in neuroblastoma: a report for the International Neuroblastoma Risk Group (INRG) Task Force

BACKGROUND

Neuroblastoma is an embryonic tumour of the sympathetic nervous system, metastatic in half of the patients at diagnosis, with a high preponderance of osteomedullary disease, making accurate evaluation of metastatic sites and response to therapy challenging. Metaiodobenzylguanidine (mIBG), taken into cells via the norepinephrine transporter, provides a sensitive and specific method of assessing tumour in both soft tissue and bone sites. The goal of this report was to develop consensus guidelines for the use of mIBG scans in staging, response assessment and surveillance in neuroblastoma.

METHODS

The International Neuroblastoma Risk Group (INRG) Task Force, including a multidisciplinary group in paediatric oncology of North and South America, Europe, Oceania and Asia, formed a subcommittee on metastatic disease evaluation, including expert nuclear medicine physicians and oncologists, who developed these guidelines based on their experience and the medical literature, with approval by the larger INRG Task Force.

RESULTS

Guidelines for patient preparation, radiotracer administration, techniques of scanning including timing, energy, specific views, and use of single photon emission computed tomography are included. Optimal timing of scans in relation to therapy and for surveillance is reviewed. Validated semi-quantitative scoring methods in current use are reviewed, with recommendations for use in prognosis and response evaluation.

CONCLUSIONS

Metaiodobenzylguanidine scans are the most sensitive and specific method of staging and response evaluation in neuroblastoma, particularly when used with a semi-quantitative scoring method. Use of the optimal techniques for mIBG in staging and response, including a semi-quantitative score, is essential for evaluation of the efficacy of new therapy.

Pupil function as an indicator for being under the influence of central nervous system-acting substances from a traffic-medicine perspective

To evaluate an individual's ability to drive safely, objective measurement methods are required. The primary aim of this study was to assess the applicability and value of infrared pupillography as an objective measurement method to indicate possible influence of central nervous system-acting substances. We exposed healthy test subjects (n = 41), as well as persons who were under the influence of drugs and/or medication (n = 105), to different light stimuli and tested the pupillary light reflex using infrared technology. The synoptic examination of numerous parameters, and the possibility of examination under various conditions, made it possible to achieve highly significant differentiation between persons who were under the influence of drugs and/or medication and control persons. Infrared pupillography represents an objective method of measuring pupil function, providing a reliable indicator of previous consumption of drugs and/or medication. In order to increase legal certainty it would thus appear desirable to make infrared pupillography a routine part of police checks in the near future.