Chronic treatment with fluvoxamine, clovoxamine, and placebo: interaction with digoxin and effects on sleep and alertness

Fluvoxamine-associated oscillopsia and a role for personalized medication dosing

A 60-year-old woman reported horizontal "shimmering" movement while reading crossword puzzles when using fluvoxamine, bupropion, quetiapine, lithium, and levothyroxine. This visual disturbance, likely oscillopsia, started after the fluvoxamine was added and waned as the fluvoxamine was tapered, disappearing after the drug was discontinued. Genetic testing to explore how the patient metabolizes these medications combined with YouScript® interaction analysis suggest that she may have had abnormally high plasma concentrations of fluvoxamine during this time. Oscillopsia may be a novel dose-dependent side effect of fluvoxamine. Genetic testing combined with YouScript has the potential to discover novel drug side effects, elucidate drug interactions and guide future prescribing decisions.

Different effects of the selective serotonin reuptake inhibitors fluvoxamine, paroxetine, and sertraline on the pharmacokinetics of fexofenadine in healthy volunteers

Although the interaction between selective serotonin reuptake inhibitors (SSRIs) and other drugs is important in the treatment of depression, there have been few studies of SSRIs concerning transporter-mediated interactions in humans. The objective of this study was to evaluate the in vivo effects of commonly used SSRIs on the pharmacokinetics of fexofenadine, a P-glycoprotein substrate.Twelve healthy volunteers (3 females and 9 males) were enrolled in this study. Each subject received a 60-mg dose of fexofenadine orally at baseline. Afterward, they were randomly assigned to receive 3 treatments with a 60-mg dose of fexofenadine after a 7-day treatment with fluvoxamine (50 mg/d), paroxetine (20 mg/d), or sertraline (50 mg/d), with 2-week intervals between the agents.Fluvoxamine pretreatment significantly increased the maximum plasma concentration, the area under the concentration time curves, and the 24-hour urinary fexofenadine excretion by 66% (P = 0.004), 78% (P = 0.029), and 78% (P < 0.001), respectively, without prolonging its elimination half-life. Paroxetine extended the elimination half-life of fexofenadine by 45% (P = 0.042), and it increased the 24-hour urinary fexofenadine excretion by 55% (P = 0.002). Sertraline did not alter any of the pharmacokinetic parameters of fexofenadine.This is the first report of the different effects of 3 commonly used SSRIs on fexofenadine pharmacokinetics in humans. Our 7-day, repeated-dose clinical study in healthy volunteers indicates that fluvoxamine and paroxetine, but not sertraline, may impact the patient exposure to fexofenadine, which is likely the result of P-glycoprotein inhibition in the small intestine and/or the liver.

The emerging importance of transporter proteins in the psychopharmacological treatment of the pregnant patient

P-glycoprotein, breast cancer resistance protein, and multidrug resistance proteins have physiological functions in placental tissue. Several antidepressants, antipsychotics, and anti-epileptic drugs have been found to be substrates of P-glycoprotein and other transporters. The extent that drugs pass through the placental barrier is likely influenced by drug transporters. The rational choice of psychoactive drugs to treat mental illness in women of child-bearing age should incorporate knowledge of both drug disposition as well as expected pharmacologic effects. This review summarizes the current data on drug transporters in the placental passage of medications, with a focus on medications used in clinical psychopharmacology.

Biomarkers for the effects of selective serotonin reuptake inhibitors (SSRIs) in healthy subjects

AIMS

Studies of novel centrally acting drugs in healthy volunteers are traditionally concerned with kinetics and tolerability, but useful information may also be obtained from biomarkers of clinical endpoints. This paper provides a systematic overview of CNS-tests used with SSRIs in healthy subjects. A useful biomarker should meet the following requirements: a consistent response across studies and drugs; a clear response of the biomarker to a therapeutic dose; a dose-response relationship; a plausible relationship between biomarker, pharmacology and pathogenesis.

METHODS

These criteria were applied to all individual tests found in studies of selective serotonin reuptake inhibitors (SSRIs), performed in healthy subjects since 1966, identified with a systematic MedLine search. Separate databases were created to evaluate the effects of single or multiple dose SSRI-studies, and for amitriptyline whenever the original report included this antidepressant as a positive control. Doses of the antidepressant were divided into high- and low-dose ranges, relative to a medium range of therapeutic doses. For each test, the drug effects were scored as statistically significant impairment/decrease (-), improvement/increase (+) or no change (=) relative to placebo.

RESULTS

56 single dose studies and 22 multiple dose studies were identified, investigating the effects of 13 different SSRIs on 171 variants of neuropsychological tests, which could be clustered into seven neuropsychological domains. Low single doses of SSRIs generally stimulated tests of attention and memory. High doses tended to impair visual/auditory and visuomotor systems and subjective performance, while showing an acceleration in motor function. The most pronounced effects were observed using tests that measure flicker discrimination (improvement at low doses: 75%, medium doses: 40%, high doses: 43% of studies); REM sleep (inconsistent decrease after medium doses, decrease in 83% of studies after high doses); and EEG recordings, predominantly in alpha (decrease in 60% and 43% of studies after low and medium doses, respectively) and in theta activity (increase in 43% and 33% of studies after medium and high doses, respectively). Amitriptyline generally impaired central nervous system (CNS) functions, which increased with doses. Multiple doses caused less pronounced effects on the reported tests. The most responsive tests to amitriptyline appeared to be EEG alpha and theta, and REM sleep duration.

CONCLUSIONS

SSRIs in healthy subjects appear to cause slight stimulating effects after low doses, which tend to diminish with dose. The most consistent effects were observed with flicker discrimination tests, EEG (alpha and beta bands), REM sleep duration, and subjective effects at higher doses. These effects are small compared with amitriptyline and other CNS-active drugs. Multiple dosing with SSRIs caused even fewer measurable differences from placebo, probably due to adaptive processes. SSRI-effects are best detected with a test battery that is sensitive to general CNS-stimulation, but such tests only comprise a very small portion of the close to 200 different methods that were found in current review.

A population-based assessment of the potential interaction between serotonin-specific reuptake inhibitors and digoxin

AIM

In vitro evidence suggests that some serotonin-specific reuptake inhibitors (SSRIs) inhibit P-glycoprotein, a multidrug efflux pump responsible for the elimination of several drugs including digoxin. We sought to determine if some SSRIs cause digoxin toxicity in the clinical setting.

METHODS

Population-based nested case-control study set in Ontario, Canada from 1994 to 2001. We studied all patients 66 years or older treated with digoxin. Prescription and hospital admission records were analysed to determine the relationship between the initiation of SSRI therapy and hospital admission for digoxin toxicity in the subsequent 30 days.

RESULTS

Among 245 305 older patients treated with digoxin, we identified 3144 cases of digoxin toxicity. After adjusting for potential confounders, we observed an increased risk of digoxin toxicity following initiation of paroxetine [odds ratio (OR) 2.8; 95% confidence interval (CI) 1.6, 4.7], fluoxetine (OR 2.9; 95% CI 1.5, 5.4), sertraline (OR 3.0; 95% CI 1.9, 4.7), and fluvoxamine (OR 3.0; 95% CI 1.5, 5.7). However, an elevated risk was also seen with tricyclic antidepressants (OR 1.5; 95% CI 1.0, 2.4) and benzodiazepines (OR 2.1; 95% CI 1.7, 2.5), drugs classes having no known pharmacokinetic interaction with digoxin. There was no statistical difference in the risk of digoxin toxicity among any of the agents tested.

CONCLUSIONS

We found no major discrepancy in the risk of digoxin toxicity after initiation of various SSRI antidepressants, suggesting that the inhibition of P-glycoprotein by sertraline and paroxetine observed in vitro is unlikely to be of major clinical significance.

Working Through the Pain

OBJECTIVES

A large percentage of employees experience persistent pain while at work. This situation can become costly to employers with large amounts of lost production-time, absenteeism, and long-term disability. The link or transition between working through (ignoring) pain and disabling pain is unknown. This paper presents the results of a controlled study examining the impact of persistent pain on performance in a working population. Benefits of early detection are discussed.

METHODS

This was a controlled, repeated measures study using 3 types of measures: questionnaires (pain, pain anxiety, daily memory, and attention mistakes); actigraphic monitoring to assure the absence of sleep deprivation; and the Performance Assessment Battery, a computer-based series of tests. Participants were studied during 3 time periods (9:00 AM, 3:00 PM, and 9:00 PM).

RESULTS

Forty participants (20 pain, 20 controls) were studied. For all tasks, pain participants were slower than controls with significant findings on 2 tasks and less accurate with significant differences on 1 task.

DISCUSSION

Unlike other studies that either induced pain or used persons with complex pain conditions, this study used participants with a low level of pain intensity and had a majority still engaged in full-time employment. Our results found that people with persistent low-level pain demonstrate a reduction in performance compared with controls. Our study revealed that using a sensitive tool to detect minor performance deficits could indicate pain interference. The early detection of pain interference would provide an opportunity for prevention programs to have a pre-emptive effect on work-related musculoskeletal disorders.

Inhibition of P-glycoprotein by newer antidepressants

Pharmacokinetic drug-drug interactions often occur at the level of P-glycoprotein (Pgp). To study possible interactions caused by the newer antidepressants we investigated citalopram, fluoxetine, fluvoxamine, paroxetine, reboxetine, sertraline, and venlafaxine and their major metabolites desmethylcitalopram, norfluoxetine, paroxetine-metabolite (paroxetine-M), desmethylsertraline, N-desmethylvenlafaxine, and O-desmethylvenlafaxine for their ability to inhibit Pgp. Pgp inhibition was studied by a fluorometric assay using calcein-acetoxymethylester as Pgp substrate and two different cell systems: L-MDR1 cells (model for human Pgp) and primary porcine brain capillary endothelial cells (pBCECs, model for the blood-brain barrier). Both cell systems proved to be suitable for the evaluation of Pgp inhibitory potency of drugs. All antidepressants tested except O-desmethylvenlafaxine showed Pgp inhibitory activity with sertraline, desmethylsertraline, and paroxetine being the most potent, comparable with the well known Pgp inhibitor quinidine. In L-MDR1 cells fluoxetine, norfluoxetine, fluvoxamine, reboxetine, and paroxetine-M revealed intermediate Pgp inhibition and citalopram, desmethylcitalopram, venlafaxine, and N-desmethylvenlafaxine were only weak inhibitors. The ranking order was similar in pBCECs. The fact that some of the compounds tested exert Pgp inhibitor effects at similar concentrations as quinidine suggests that pharmacokinetic drug-drug interactions between the newer antidepressants and Pgp substrates should now be thoroughly studied in vivo.

Fluvoxamine: a review of its therapeutic potential in the management of anxiety disorders in children and adolescents

Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) which may be used for the management of anxiety disorders in children and adolescents. Absorption of fluvoxamine was similar in adolescents to that in adults, which suggests that the maximum dosage of the drug for patients aged between 12 and 17 years can be as high as 300 mg/day. However, steady-state plasma fluvoxamine [corrected] concentrations were 2 to 3 times higher in children (aged between 6 and 11 years) than in adolescents; thus, the maximum fluvoxamine dosage recommended for children is 200 mg/day. Fluvoxamine (50 to 300 mg/day) for 8 to 16 weeks significantly reduced symptoms of obsessive-compulsive disorder (OCD) [measured across multiple assessment scales] compared with placebo in a well controlled trial in paediatric patients (n = 120) or from baseline in noncomparative trials in adolescent (n = 20) or paediatric (n = 16) patients. Improvements with fluvoxamine (up to 200 mg/day) were observed for up to 1 year in 98 patients with OCD in a noncomparative trial. The drug (up to 250 or 300 mg/day) also improved symptoms of anxiety compared with placebo in an 8-week well controlled trial in 128 paediatric patients with social phobia, separation anxiety disorder or generalised anxiety disorder (GAD). Fluvoxamine (50 to 300 mg/day) appears to be well tolerated in paediatric patients, with most adverse events with the drug (except abdominal discomfort, which occurred more often in patients receiving fluvoxamine) occurring with a similar incidence to those with placebo. The most common adverse events involved the central nervous system or gastrointestinal system. Most adverse events reported by paediatric patients with OCD were similar to those reported by adults. In conclusion, fluvoxamine is generally well tolerated and has demonstrated short-term efficacy compared with placebo in the treatment of OCD, and social phobia, separation anxiety disorder or GAD in well controlled trials in paediatric patients. Reductions in symptoms of anxiety with fluvoxamine have been observed for up to 1 year in children and adolescents with OCD. However, there are currently no comparative trials of fluvoxamine with other pharmacological agents. In the absence of such trials, current consensus opinion recommends that when pharmacotherapy is indicated, fluvoxamine, like other SSRIs, can be used as first-line treatment for anxiety disorders, particularly OCD, in paediatric patients. However, direct comparisons are required to assess the relative efficacy and tolerability of pharmacological agents in order to make firm recommendations for the treatment of anxiety disorders in this patient group.

Fluvoxamine as an adjunctive agent in schizophrenia

Schizophrenia is a common mental disorder that has an early onset and rates high as a cause of medical disability. Antipsychotic agents are the mainstay of treatment but response is often inadequate. Negative symptoms (disturbances in volition, social interaction and affective functions) are particularly difficult to treat and form a major obstacle to rehabilitation. A promising approach to improve response of negative symptoms has been to add a selective serotonin reuptake inhibitor (SSRI) antidepressant to antipsychotic treatment. This review examines evidence pertaining to the efficacy, tolerability, and safety of the SSRI fluvoxamine, combined with antipsychotic agents, in the treatment of negative symptoms in schizophrenia. Important methodological issues, such as differentiating primary and secondary negative symptoms, are discussed. The balance of available evidence indicates that fluvoxamine can improve primary negative symptoms in chronic schizophrenia patients treated with typical antipsychotics and suggests that it may also do so in some patients treated with clozapine. This combination is generally safe and well tolerated although, as antipsychotic drug concentrations may be elevated, attention to dose and drug monitoring should be considered appropriately. Combination with clozapine may require particular caution because of potential toxicity if serum clozapine levels rise steeply. The fluvoxamine doses effective in augmentation are lower than those usually used to treat depression. Evidence regarding the use of fluvoxamine augmentation to treat phenomena, such as obsessions and aggression, which may be associated with schizophrenia, is also examined. An important goal of future studies will be to define which patient groups can benefit from combined treatment.

Fluvoxamine. An updated review of its use in the management of adults with anxiety disorders

Fluvoxamine is a potent and selective serotonin reuptake inhibitor (SSRI) that has little or no effect on other monoamine reuptake mechanisms. Relative to other SSRIs, fluvoxamine is a weak inhibitor of cytochrome P450 (CYP) 2D6, a moderate inhibitor of CYP2C19 and CYP3A4 and a potent inhibitor of CYP1A2. In randomised, double-blind trials. fluvoxamine 100 to 300 mg/day for 6 to 10 weeks significantly reduced symptoms of obsessive-compulsive disorder (OCD) compared with placebo. Response rates of 38 to 52% have been reported with fluvoxamine, compared with response rates of 0 to 18% with placebo. In patients with OCD, fluvoxamine had similar efficacy to that of clomipramine and, in smaller trials, the SSRIs paroxetine and citalopram and was significantly more effective than desipramine. Maintenance therapy with fluvoxamine may reduce the likelihood of relapses in up to 67% of patients with OCD. Fluvoxamine < or = 300 mg/day for 6 to 8 weeks was as effective as imipramine in patients with panic disorder, and significantly more effective than placebo. In addition, treatment with fluvoxamine < or = 300 mg/day for > or = 8 weeks improved symptoms of social phobia (social anxiety disorder), post-traumatic stress disorder (PTSD), pathological gambling, compulsive buying, trichotillomania, kleptomania, body dysmorphic disorder, eating disorders and autistic disorder. Large trials comparing the efficacy of fluvoxamine and other SSRIs in patients with anxiety disorders are warranted. Fluvoxamine is generally well tolerated; in postmarketing studies, nausea was the only adverse event occurring in >10% of patients with less commonly reported events including somnolence, asthenia, headache, dry mouth and insomnia. Fluvoxamine is associated with a low risk of suicidal behaviour, sexual dysfunction and withdrawal syndrome. Fewer anticholinergic or cardiovascular events are associated with fluvoxamine than tricyclic antidepressants. Although comparative data are lacking, the tolerability profile of fluvoxamine appears to be broadly similar to those of other SSRIs.

CONCLUSION

Fluvoxamine has demonstrated short term efficacy in the treatment of OCD, panic disorder, social phobia, PTSD and in a range of obsessive-compulsive spectrum disorders. The drug is as effective as clomipramine in patients with OCD but appears to have a better tolerability profile. On the basis of current treatment guidelines, fluvoxamine, like other SSRIs, is recommended as first-line treatment for a number of anxiety disorders. It appears to offer some pharmacokinetic advantages and a different drug interaction profile to the other SSRIs with a broadly similar spectrum of adverse events. However, direct comparisons are required to assess the relative efficacy and tolerability of the different agents of this drug class.

Overview of the pharmacokinetics of fluvoxamine

The pharmacokinetics of fluvoxamine, a selective serotonin reuptake inhibitor (SSRI) with antidepressant properties, are well established. After oral administration, the drug is almost completely absorbed from the gastrointestinal tract, and the extent of absorption is unaffected by the presence of food. Despite complete absorption, oral bioavailability in man is approximately 50% on account of first-pass hepatic metabolism. Peak plasma fluvoxamine concentrations are reached 4 to 12 hours (enteric-coated tablets) or 2 to 8 hours (capsules, film-coated tablets) after administration. Steady-state plasma concentrations are achieved within 5 to 10 days after initiation of therapy and are 30 to 50% higher than those predicted from single dose data. Fluvoxamine displays nonlinear steady-state pharmacokinetics over the therapeutic dose range, with disproportionally higher plasma concentrations with higher dosages. Plasma fluvoxamine concentrations show no clear relationship with antidepressant response or severity of adverse effects. Fluvoxamine undergoes extensive oxidative metabolism, most probably in the liver. Nine metabolites have been identified, none of which are known to be pharmacologically active. The specific cytochrome P450 (CYP) isoenzymes involved in the metabolism of fluvoxamine are unknown. CYP2D6, which is crucially involved in the metabolism of paroxetine and fluoxetine, appears to play a clinically insignificant role in the metabolism of fluvoxamine. The drug is excreted in the urine, predominantly as metabolites, with only negligible amounts ( < 4%) of the parent compound. Fluvoxamine shows a biphasic pattern of elimination with a mean terminal elimination half-life of 12 to 15 hours after a single oral dose; this is prolonged by 30 to 50% at steady-state. Plasma protein binding of fluvoxamine (77%) is low compared with that of other SSRIs. Fluvoxamine pharmacokinetics are substantially unaltered by increased age or renal impairment. However, its elimination is prolonged in patients with hepatic cirrhosis. Fluvoxamine inhibits oxidative drug metabolising enzymes (particularly CYP1A2, and less potently and much less potently CYP3A4 and CYP2D6, respectively) and has the potential for clinically significant drug interactions. Drugs whose metabolic elimination is impaired by fluvoxamine include tricyclic antidepressants (tertiary, but not secondary, amines), alprazolam, bromazepam, diazepam, theophylline, propranolol, warfarin and, possibly, carbamazepine. Fluvoxamine is a second generation antidepressant that selectively inhibits neuronal reuptake of serotonin (5-hydroxytryptamine; 5-HT). Fluvoxamine exhibits antidepressant activity similar to that of the tricyclic antidepressants, but has a somewhat improved tolerability profile, particularly with respect to a lower incidence of anticholinergic effects and reduced cardiotoxic potential. However, gastrointestinal adverse effects, especially nausea, are seen more frequently with fluvoxamine than with the tricyclic antidepressants. Fluvoxamine does not have an asymmetric carbon in its structure (fig. 1) and therefore does not exist as optical isomers. For this reason, the potentially confounding problem of stereoisomerism does not arise with fluvoxamine.

Pharmacokinetic optimisation of therapy with newer antidepressants

Since the early 1950s, when imipramine was first introduced, a whole series of antidepressants with differences in structures, neurochemical effects and pharmacokinetics have been developed. Structurally or functionally, they have been classified as tricyclic antidepressants (TCAs), tetracyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs). In addition, there is a series of antidepressants with unique structures. Many of the newer TCAs appear to have shorter half-lives than the standard TCAs (e.g. imipramine), allowing for the possibility of a more rapid response, but requiring the drugs to be given in multiple daily doses, which may reduce patient compliance. The short time to peak plasma concentration (tmax) can also lead to rapid onset of adverse effects. The tetracyclic antidepressants have longer elimination half-lives (t1/2) than the TCAs, but there is only very minimal evidence for a relationship between drug concentrations in the blood and clinical response. The triazolopyridines, like the newer TCAs, show pharmacokinetic evidence for rapid onset of adverse effects and the need for multiple daily doses due to short tmax and t1/2. The newer MAOIs are a significant addition to therapy, as the rapid binding action of these medications increases their safety margin with regard to tyramine interactions. Further information in this area is required. In addition, moclobemide has pharmacokinetic features that are clinically beneficial (e.g. aging and renal dysfunction have little effect on the elimination of the drug), but also features that are not beneficial (e.g. nonlinear pharmacokinetics). Among the SSRIs, there are a range of t1/2 values for the parent drugs, from relatively short t1/2 values of less than 24 hours (paroxetine, fluvoxamine) to among the longest found (e.g. 2 days for fluoxetine). Only 2 of the agents (sertraline and citalopram) have linear pharmacokinetics, and 1 drug has nonlinear pharmacokinetics within the usual therapeutic range (fluvoxamine). Once a therapeutic blood concentration is established, linearity is helpful in avoiding the small dose changes and repeated rechecking of concentrations of medications that would be required for those agents with nonlinear pharmacokinetics. Sertraline stands out as having the best effects on behaviour among all antidepressants. However, fluoxetine and fluvoxamine are least likely to penetrate into breast milk. All 3 of the structurally unique newer antidepressants [amfebutamone (bupropion), viloxazine venlafaxine] have relatively short tmax values (1 to 2 hours), which may relate to the early onset of adverse effects. Amfebutamone has the benefits of linear pharmacokinetics with potential for defined therapeutic blood concentrations, lack of effect of liver enzymes on metabolism of the drug, and lack of significant effects of either aging or hepatic dysfunction on elimination of the drug. Thus, the antidepressants best suited for pharmacokinetic optimisation of therapy are the following: desipramine, sertraline, fluvoxamine, citalopram and amfebutamone.