Pharmacokinetics of reboxetine in healthy volunteers. Single against repeated oral doses and lack of enzymatic alterations

Noradrenergic Enhancement of Motor Learning, Attention, and Working Memory in Humans

BACKGROUND

Noradrenaline has an important role as a neuromodulator of the central nervous system. Noradrenergic enhancement was recently shown to enhance glutamate-dependent cortical facilitation and long term potentiation-like plasticity. As cortical excitability and plasticity are closely linked to various cognitive processes, here we aimed to explore whether these alterations are associated with respective cognitive performance changes. Specifically, we assessed the impact of noradrenergic enhancement on motor learning (serial reaction time task), attentional processes (Stroop interference task), and working memory performance (n-back letter task).

METHODS

The study was conducted in a cross-over design. Twenty-five healthy humans performed the respective cognitive tasks after a single dose of the noradrenaline reuptake inhibitor reboxetine or placebo administration.

RESULTS

The results show that motor learning, attentional processes, and working memory performance in healthy participants were improved by reboxetine application compared with placebo.

CONCLUSIONS

The results of the present study thus suggest that noradrenergic enhancement can improve memory formation and executive functions in healthy humans. The respective changes are in line with related effects of noradrenaline on cortical excitability and plasticity.

Acute and Chronic Noradrenergic Effects on Cortical Excitability in Healthy Humans

Background

Noradrenaline is a major neuromodulator in the central nervous system, and it is involved in the pathophysiology of diverse neuropsychiatric diseases. Previous transcranial magnetic stimulation studies suggested that acute application of selective noradrenaline reuptake inhibitors enhances cortical excitability in the human brain. However, other, such like clinical effects, usually require prolonged noradrenaline reuptake inhibitor treatment, which might go along with different physiological effects.

Methods

The purpose of this study was to investigate the acute and chronic effects of the selective noradrenaline reuptake inhibitor reboxetine on cortical excitability in healthy humans in a double-blind, placebo-controlled, randomized crossover study. Sixteen subjects were assessed with different transcranial magnetic stimulation measurements: motor thresholds, input-output curve, short-latency intracortical inhibition and intracortical facilitation, I-wave facilitation, and short-interval afferent inhibition before and after placebo or reboxetine (8 mg) single-dose administration. Afterwards, the same subjects took reboxetine (8 mg/d) consecutively for 21 days. During this period (subjects underwent 2 experimental sessions with identical transcranial magnetic stimulation measures under placebo or reboxetine), transcranial magnetic stimulation measurements were assessed before and after drug intake.

Results

Both single-dose and chronic administration of reboxetine increased cortical excitability; increased the slope of the input-output curve, intracortical facilitation, and I-wave facilitation; but decreased short-latency intracortical inhibition and short-interval afferent inhibition. Moreover, chronic reboxetine showed a larger enhancement of intracortical facilitation and I-wave facilitation compared with single-dose application.

Conclusions

The results show physiological mechanisms of noradrenergic enhancement possibly underlying the functional effects of reboxetine regarding acute and chronic application.

Acute and chronic effects of noradrenergic enhancement on transcranial direct current stimulation-induced neuroplasticity in humans

KEY POINTS

Chronic administration of the selective noradrenaline reuptake inhibitor (NRI) reboxetine (RBX) increased and prolonged the long-term potentiation-like plasticity induced by anodal transcranial direct current stimulation (tDCS) for over 24 h. Chronic administration of RBX converted cathodal tDCS-induced long-term depression-like plasticity into facilitation for 120 min. Chronic noradrenergic activity enhancement on plasticity of the human brain might partially explain the delayed therapeutic impact of selective NRIs in depression and other neuropsychiatric diseases.

ABSTRACT

Noradrenaline affects cognition and motor learning processes via its impact on long-term potentiation (LTP) and depression (LTD). We aimed to explore the impact of single dose and chronic administration of the selective noradrenaline reuptake inhibitor (NRI) reboxetine (RBX) on plasticity induced by transcranial direct current stimulation (tDCS) in healthy humans via a double-blinded, placebo-controlled, randomized crossover study. Sixteen healthy volunteers received placebo or single dose RBX (8 mg) before anodal or cathodal tDCS of the primary motor cortex. Afterwards, the same subjects took RBX (8 mg day-1 ) consecutively for 21 days. During this period, two additional interventions were performed (RBX with anodal or cathodal tDCS), to explore the impact of chronic RBX treatment on plasticity. Plasticity was monitored by motor-evoked potential amplitudes elicited by transcranial magnetic stimulation. Chronic administration of RBX increased and prolonged the LTP-like plasticity induced by anodal tDCS for over 24 h. Chronic RBX significantly converted cathodal tDCS-induced LTD-like plasticity into facilitation, as compared to the single dose condition, for 120 min after stimulation. The results show a prominent impact of chronic noradrenergic enhancement on plasticity of the human brain that might partially explain the delayed therapeutic impact of selective NRIs in depression and other neuropsychiatric diseases.

Increased fetal blood pressure response to maternal norepinephrine after pharmacological inhibition of norepinephrine uptake in pregnant sheep

OBJECTIVE

Norepinephrine (NE) is elevated in pregnancies complicated by preeclampsia (PE). Specific uptake of NE by the NE transporter (NET) plays a central role as regulator of NE levels. Expression of NET is reduced in placentas from PE pregnancies. To study adverse fetal effects of reduced NET expression on the placental buffering capacity, the NET was pharmacologically blocked by a specific uptake inhibitor reboxetine.

STUDY DESIGN

We evaluated the effect of NE uptake inhibition on maternal and fetal arterial blood pressure responses to increasing maternal doses of NE in 10 chronically prepared fetal sheep. Arterial blood pressure was monitored continuously during increasing doses of i.v. NE.

RESULTS

NET inhibition increased both fetal and maternal mean arterial blood pressure (p < 0.001, respectively).

CONCLUSION

Reuptake by NET appears to be a mechanism protecting the fetus from NE. A reduced uptake capacity in preeclamptic pregnancies due to reduced NE uptake may lead to increased fetal arterial blood pressure.

The AGNP-TDM Expert Group Consensus Guidelines: focus on therapeutic monitoring of antidepressants

Therapeutic drug monitoring (TDM) of psychotropic drugs such as antidepressants has been widely introduced for optimization of pharmacotherapy in psychiatric patients. The interdisciplinary TDM group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) has worked out consensus guidelines with the aim of providing psychiatrists and TDM laboratories with a tool to optimize the use of TDM. Five research-based levels of recommendation were defined with regard to routine monitoring of drug plasma concentrations: (i) strongly recommended; (ii) recommended; (iii) useful; (iv) probably useful; and (v) not recommended. In addition, a list of indications that justify the use of TDM is presented, eg, control of compliance, lack of clinical response or adverse effects at recommended doses, drug interactions, pharmacovigilance programs, presence of a genetic particularity concerning drug metabolism, and children, adolescents, and elderly patients. For some drugs, studies on therapeutic ranges are lacking, but target ranges for clinically relevant plasma concentrations are presented for most drugs, based on pharmacokinetic studies reported in the literature. For many antidepressants, a thorough analysis of the literature on studies dealing with the plasma concentration-clinical effectiveness relationship allowed inclusion of therapeutic ranges of plasma concentrations. In addition, recommendations are made with regard to the combination of pharmacogenetic (phenotyping or genotyping) tests with TDM. Finally, practical instructions are given for the laboratory practitioners and the treating physicians how to use TDM: preparation of TDM, drug analysis, reporting and interpretation of results, and adequate use of information for patient treatment TDM is a complex process that needs optimal interdisciplinary coordination of a procedure implicating patients, treating physicians, clinical pharmacologists, and clinical laboratory specialists. These consensus guidelines should be helpful for optimizing TDM of antidepressants.

The selective norepinephrine reuptake inhibitor antidepressant reboxetine: pharmacological and clinical profile

Reboxetine is the first commercially available norepinephrine reuptake inhibitor developed specifically as a first line therapy for major depressive disorder. In vitro and in vivo pharmacological studies indicated that reboxetine methanesulphonate has high affinity and selectivity for the human norepinephrine transporter over the serotonin and dopamine transporters. Pharmacological specificity is further demonstrated by the absence of affinity for 45 transmitter receptors and CNS targets. Pharmacokinetic studies demonstrated that reboxetine is suitable for twice daily administration (8-10 mg/day) and that it exhibits minimal drug-drug interactions. The starting dose of reboxetine should be reduced in the elderly, in patients with renal or hepatic impairment, or in patients receiving potent CYP3A inhibitors. A total of 20 phase II/III clinical studies comprising placebo-controlled, active comparator-controlled and open-label uncontrolled studies in both short-term and long-term treatment of major depression have been conducted. In the treatment of major depression, reboxetine was superior to placebo in 5 of 12 short- or long-term placebo-controlled studies and was comparable in efficacy to active comparators in 3 out of 3 active-controlled studies. Unlike conventional tricyclic antidepressants (TCAs), reboxetine had only minimal sedative and cardiovascular liabilities, probably due to increased pharmacological specificity of reboxetine as compared with TCAs. Unlike serotonin reuptake inhibitors, this selective and specific norepinephrine reuptake inhibitor demonstrated a distinct side-effect profile with diminishing sexual dysfunction and GI side effects. The availability of this agent has afforded patients suffering from major depressive disorder a new class of agents to combat the debilitating consequence of this psychiatric disease. The demonstrated pharmacological specificity of this compound has provided the psychopharmacology community with a tool to elucidate the role of norepinephrine in brain functions. Testing this agent in different animal models has enabled the exploration of the role of modulation of norepinephrine tone in the therapy of CNS disorders beyond depression.

Analysis of reboxetine, a novel antidepressant drug, in pharmaceutical tablets by capillary electrophoresis and derivative spectrophotometry

The recent antidepressant drug reboxetine was quantified in pharmaceutical tablets by derivative spectrophotometry and capillary zone electrophoresis. The feasible sample pretreatment consists of a single extraction with a pH 2.5 phosphate buffer, centrifugation and dilution. For the spectrophotometric assay, the fourth derivative of the absorbance was used which gave satisfactory results in terms of accuracy (mean recovery 99.7%) and precision (mean RSD 3.4%). The electrophoretic experiments were carried out using the shortest effective length of the capillary (8.5 cm) in order to obtain a very rapid separation of reboxetine and dibenzepine used as the internal standard. Using a pH 2.5, 50 mM phosphate buffer as the background electrolyte, each analysis lasted less than 2.5 min. Accuracy (101.3%) and precision (1.5%) were very good.

Bioanalysis of racemic reboxetine and its desethylated metabolite in a therapeutic drug monitoring setting using solid phase extraction and HPLC

Reboxetine is a new antidepressant drug acting as a potent and selective noradrenaline reuptake inhibitor on the noradrenergic neuronal system. Because of an expected interindividual variability in drug metabolism in the clinical practice the need for therapeutic drug monitoring routines in psychiatry is always a prominent feature. In this application, the preferred bioanalytic methodology was solid phase extraction combined with reversed-phase high-performance liquid chromatography and ultraviolet detection at 210 nm. The technique proved reliable, with interday and intraday variation of less than 5% and a quantification limit for reboxetine and one of its main metabolites O-desethylreboxetine (O-reboxetine) at 5 and 30 nmol/L, respectively. The method was applied on serum samples from 38 patients treated chronically with reboxetine. These samples were drawn as trough levels in steady state with a dosage range of 2-16 mg/day. They evidenced a mean reboxetine concentration that was fairly linear and dose proportional, although the variance in concentration was large between patients, even those taking the same dosage. O-reboxetine was detected in quantifiable amounts in only 1 of the 38 patients (<3%). In conclusion, these results suggest that a routine reboxetine therapeutic drug monitoring service that is robust enough to produce reliable and reproducible results may be introduced into everyday clinical practice.

Reboxetine: a selective norepinephrine reuptake inhibitor for the treatment of depression

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and tolerability of reboxetine in the treatment of major depressive illness.

DATA SOURCES

A MEDLINE search restricted to English-language literature was conducted (1966 to July 1999). Abstracts and posters presented at meetings were also reviewed. DATA EXTRACTION/STUDY SELECTION: Studies currently available were conducted in Europe. Data from clinical trials were reviewed to gather information specific to efficacy analysis, pharmacokinetic parameters, tolerability profiles, and drug-drug interactions. Information on reboxetine was compared with other antidepressant therapies when appropriate data were available.

DATA SYNTHESIS

Reboxetine is a selective norepinephrine reuptake inhibitor shown to be an effective agent in the treatment of major depressive illness. In clinical trials, reboxetine was effective in decreasing mean total scores of the Hamilton Rating Scale for Depression in adult populations. Improvements were similar between reboxetine and desipramine and imipramine, as well as fluoxetine. Reboxetine is relatively well tolerated, with insomnia, sweating, constipation, and dry mouth being commonly reported adverse events. Hypotension and urinary hesitancy occur at lower rates than with the tricyclics, and compared with fluoxetine, reboxetine is associated with lower rates of nausea, somnolence, and diarrhea. Dosage adjustments may be appropriate in elderly patients and those with renal and hepatic impairment.

CONCLUSIONS

Reboxetine has received two letters of approval from the Food and Drug Administration for the treatment of major depression in adults. Upon completion of an additional US clinical study, reboxetine is likely to become a first-line agent in the management of depressive illness and a promising alternative for patients who have failed treatment with or do not tolerate serotonergic antidepressants.

Pharmacokinetics of single-dose reboxetine in volunteers with renal insufficiency

Reboxetine is a new selective norepinephrine reuptake inhibitor (selective NRI) for the short- and long-term treatment of depression that is effective and well tolerated at a dose of 8 to 10 mg/day. This study assessed the pharmacokinetics of reboxetine in volunteers with renal impairment. A single 4 mg dose of reboxetine was administered to a total of 18 volunteers with mild (n = 6), moderate (n = 6), or severe (n = 6) renal impairment (creatinine clearance: 56-64, 26-51, and 9-19 ml/min, respectively), and reboxetine concentrations were measured in plasma by HPLC. Mean AUC infinity increased by 43% (mild vs. severe; p < 0.01) as renal function declined, while renal clearance and total urinary excretion of unchanged reboxetine decreased by 67% and 62%, respectively (mild vs. severe; p < 0.01 for both parameters). tmax and t1/2 were not significantly different between groups. In comparison with historical data from young healthy volunteers, AUC infinity and t1/2 are at least doubled in volunteers with renal impairment, while CLr is halved. This pharmacokinetic study has shown that increasing renal dysfunction leads to increasing systemic exposure to reboxetine, particularly in severe renal insufficiency, although reboxetine was well tolerated by all volunteers. Thus, a reduction of the starting dose of reboxetine to 2 mg twice daily would be prudent in patients with renal dysfunction.

Hemodynamic effects of reboxetine in healthy male volunteers

BACKGROUND

Reboxetine [(R,S)-2[(R,S)-alpha-(2-ethoxyphenoxy)benzyl]morpholine methanesulfonate] is a racemic compound that consists of equal proportions of R,R- and S,S-enantiomers. This study investigated the hemodynamic effects of reboxetine and the R,R-enantiomer compared with placebo in volunteers. The pharmacokinetics of reboxetine and its enantiomers were also investigated in the study.

METHODS

Nine healthy, male volunteers received single doses of 4 mg reboxetine, 2 mg R,R-enantiomer, and placebo at weekly intervals. Reboxetine and the R,R-enantiomer were well tolerated in all volunteers.

RESULTS

The heart rates of patients in the supine and standing positions were increased after reboxetine administration compared with the R,R-enantiomer (P < .05, except supine heart rate at 6 hours) and placebo (P < .05). Supine systolic and diastolic blood pressure was also increased by 3 +/- 4 and 1 +/- 4 mm Hg, respectively, after reboxetine compared with R,R-enantiomer (-2 +/- 4 and -4 +/- 3 mm Hg) and placebo (-4 +/- 4 and -4 +/- 4 mm Hg) administration. The systolic and diastolic blood pressure measurements for subjects while standing did not differ significantly among treatments. There was no significant difference between the maximum plasma concentration, mean time to maximum plasma concentration, plasma half-life, or area under the plasma concentration-time curve (AUC) of the R,R-enantiomer after reboxetine or R,R-enantiomer administration. The ratio of the mean AUC values for the R,R- and S,S-enantiomers was 2.1.

CONCLUSION

These findings suggest that the S,S-enantiomer is responsible for the hemodynamic effects of reboxetine in humans. Increases in supine blood pressure after reboxetine administration may be interpreted as regression to the mean value and not caused by any treatment effect.

Psychopharmacology of depression in the next millennium

Over the last half of the 20th century, there have been a series of psychopharmacologic strategies for treatment of depression. As we approach the next century, new therapies in varying stages of American release are being developed. This review will focus on information available for the following proposed antidepressants: 1) reboxetine, a norepinephrine selective reuptake inhibitor; 2) milnacipran, a combined serotonin/norepinephrine reuptake inhibitor; 3) a new enantiomer of fluoxetine, a selective serotonin reuptake inhibitor; 4) duloxetine, another combined serotonin/norepinephrine reuptake inhibitor; 5) sunepitron, a combined 5-HT1A agonist and a2 antagonist; and 6) MK-869, a substance P inhibitor. Finally, other possible developing directions will be reviewed, including corticotropin-releasing factor.

Absolute bioavailability of reboxetine enantiomers and effect of gender on pharmacokinetics

The absolute bioavailability of reboxetine enantiomers was assessed in six male and six female volunteers. In a two-way crossover study, subjects received 1.0 mg reboxetine orally and 0.3 mg reboxetine as an intravenous bolus. The R,R(-) and S,S(+) enantiomers in serial plasma and urine samples were determined by a validated LC-MS-MS method. There were no significant differences between treatments for clearance or dose-corrected AUC(0-infinity) values. The absolute bioavailability was 0.919 and 1.02 for R,R(-) reboxetine and S,S(+) reboxetine, respectively. A secondary objective of the study was to assess gender effects on pharmacokinetics of the enantiomers. Significant differences in volume of distribution between genders were observed, but differences in weight-corrected volumes were not significant. Weight-corrected systemic clearance and oral clearance tended to be lower in males, but this difference reached statistical significance only for weight-corrected oral clearance of R,R(-) reboxetine. C(max) after oral administration was 40 and 48% higher in women than men for R,R(-) reboxetine and S,S(+) reboxetine, respectively. These results indicate that reboxetine enantiomers are well absorbed after oral administration and that little first-pass metabolism occurs. There are no clinically significant effects of gender on the pharmacokinetics of reboxetine enantiomers.

A simplified account of drug accumulation and steady-state dose equivalences

The accumulation of medication taken regularly can influence its clinical effects, cumulative toxicities and steady-state equivalent doses to similar agents, and the elimination of concurrent medications. A basic expression of drug accumulation, the Unit Dose Accumulation Ratio (UDAR), is defined as the ratio of the day-average blood drug concentration at steady-state to the peal blood drug concentration after one dose. In a single-compartment analysis the UDAR is found to equal 0.0601 multiplied by the elimination half-life (in hours). The UDARs estimated in this way approximate those found from measurements of valproic acid, desipramine, and reboxetine. Further modeling reveals that in common situations graduality of release has only small effects on UDARs. Extension to multiexponential elimination is described by simple expressions in terms of ratios of kinetic coefficients. Modeling of accumulation with biexponential elimination is depicted on a graph. Several applications of the UDAR are illustrated. The UDAR permits determination of steady-state dose equivalences from single dose equivalences and vice-versa. This facilitates medication interchange, as in clinical withdrawal management by replacement of short-acting sedative-hypnotics with long-acting agents, e.g., alprazolam with clonazepam. The UDAR reflects tolerance, e.g., if 30-mg flurazepam equals 4-mg lorazepam, the UDAR indicates that at steady-state, 30 mg/day of flurazepam approximates 21 mg/day of lorazepam. The UDAR can estimate total exposure, e.g., to organic chlorine. The UDAR complements methods described previously for drug dose prediction and blood drug level monitoring that were simplified by expressing blood levels as averages over the day.

Review of the pharmacokinetics and metabolism of reboxetine, a selective noradrenaline reuptake inhibitor

The pharmacokinetics and metabolism of reboxetine, a selective noradrenaline reuptake inhibitor, in humans and animal models are reviewed here. Reboxetine has potent antidepressant activity, low affinity for alpha-adrenergic and muscarinic receptors and low toxicity in animals. It is a mixture of (R,R) and (S,S) enantiomer, the latter being more potent but no qualitative differences in pharmacodynamic properties are observed between the two. Humans rapidly absorb reboxetine (tmax about 2 h) with a terminal half-life of elimination (t1/2) of 13 h, allowing twice-daily administration. Animal models also rapidly absorb reboxetine (tmax 0.5-2 h) but t1/2 was 1-2 h. Food does not affect bioavailability. There were no major inter-species differences in the metabolic profile of reboxetine. Elimination is principally renal in humans and monkeys. Reboxetine has linear pharmacokinetics in young, healthy males for single doses of 1-5 mg and in elderly, female depressed patients (up to 4 mg b.i.d.). Multiple dosing, gender or liver insufficiency had no significant effects on the pharmacokinetics. Elderly (particularly frail elderly) patients and patients with severe renal impairment may need dose reduction. Reboxetine shows no clinically relevant interaction with lorazepam and has no inhibitory effects on the major enzymes involved in drug metabolism. It may be possible to use reboxetine in combination with monoamine oxidase inhibitors as it has no inhibitory effect on this enzyme; in addition, it may protect patients against tyramine-induced reactions. In conclusion, reboxetine seems to be an antidepressant with negligible interference with the pharmacokinetics of other drugs thus fewer drug-drug interactions are expected.