Reboxetine – a ‘NaRI’ Graylands Hospital Drug Bulletin 2002 Vol 10 No3 November ISSN 1323-1251 Where is its place in therapy? ! There is no convincing evidence to suggest an overall advantage in efficacy, relapse prevention or speed of onset with reboxetine over existing antidepressants. ! It may be useful in SSRI resistant depression. More evidence is needed to support its use in indications such as anxiety, OCD and panic disorder. ! Noradrenergic deficiency differs to serotonergic deficiency and is associated with impaired attention, problems concentrating, fatigue and memory deficits. These symptoms may respond best to treatment with a selective noradrenergic agent, such as reboxetine. ! Like the SSRIs, reboxetine offers advantages over the tricyclics and the MAOIs in terms of safety. ! Unlike the SSRIs & TCAs it does not significantly interact with cytochrome P450 enzymes. ! Reboxetine is associated with “pseudo-anticholinergic” symptoms (not due to direct action on cholinergic receptors). This may preclude its use in certain patients. of CYP3A4 and CYP2D6 (not thought to be Reboxetine (Edronax) is the latest addition clinically relevant when used within to the choice of antidepressants available on recommended dose range). The half-life is the PBS in Australia. It is indicated for the approximately 12 hours (consistent with twice treatment and prevention of relapse of major daily dosing) and excretion is mainly via the depression. So what advantages, if any, does renal route. it offer over existing agents? Efficacy Mode of action Depression Reboxetine is the first selective noradrenaline Short-term trials have shown reboxetine to be reuptake-inhibitor (“NaRI”) to be introduced (1,2,3,4) more effective than placebo and and has only a weak effect on serotonin (4,5) similarly effective to fluoxetine , reuptake and no effect on dopamine uptake. (6,7) (1) imipramine and desipramine in the It has no significant affinity for cholinergic or treatment of major depression. In a subset of adrenergic receptors, however this is not severely depressed patients, reboxetine was necessarily reflected in its side-effect profile. (5) significantly more effective than fluoxetine . Pharmacokinetics In a long-term study (up to 1 yr), reboxetine Reboxetine is well-absorbed following oral demonstrated superior efficacy to placebo in administration and can be taken without prevention of relapse and recurrence of regard to food. Cytochrome P4503A4 is (3) depression . At the 12 month assessment, primarily responsible for the hepatic 78% of patients treated with reboxetine were metabolism of reboxetine; the major classified as in remission, compared with 45% metabolite is inactive. It is a weak inhibitor of patients in the placebo group. Graylands Hospital Drug Bulletin 2002 Vol 10 No 3 November - 1 – Reboxetine is not on the hospital formulary as yet. Social functioning Reboxetine should be used with caution in Claims are also made regarding significant men with prostatic enlargement (see below). improvement in social interaction and (8) Is it safe to use in pregnancy and functioning compared with fluoxetine . breastfeeding? However, this is based on trials using a less Pregnancy - Category B1. Information complex questionnaire (9) which was recently regarding exposure to reboxetine during developed and validated by the manufacturer. pregnancy is limited. A few cases are This result requires confirmation, ideally with described in the literature but insufficient the use of established scales. information is available to make an Other areas assessment of safety (17). Core symptoms of depression, such as anxiety The use of reboxetine whilst breastfeeding is and agitation, can often be exacerbated by not recommended. A literature search antidepressants. A pooled analysis found that revealed no case reports. reboxetine was not associated with an increased incidence of treatment-emergent Side effect profile anxiety or agitation (10). Patients who suffered Adverse events that occurred significantly from generalised anxiety disorder were more frequently with reboxetine than placebo excluded from these trials, so these findings are summarised in Table 1. may not extend to treatment of these patients. Reboxetine is mostly associated with Small studies have shown potential for the use anticholinergic-type symptoms. This is not of reboxetine in panic disorder (11,12), due to direct blockade of cholinergic Parkinson’s Disease (13,14) and possibly receptors but to indirect reduction of net bulimia (15) (though constipation may reduce parasympathetic tone, resulting from its suitability in this area). More evidence is increased sympathetic tone. They are needed to support its use in these situations. probably more of a nuisance than a danger, and will generally subside with time. When NOT to use reboxetine However, they may be significant enough to The use of reboxetine in conjunction with cause discontinuation in a number of patients. MAOIs is not recommended. The manufacturer also contraindicates its use in In general, reboxetine was better tolerated patients with narrow angle glaucoma due to than imipramine and desipramine. Compared its weak mydriatic effect. to fluoxetine, reboxetine was associated with a higher incidence of anticholinergic-type When to use reboxetine with CAUTION effects, such as dry mouth and constipation Similarly to other antidepressants, reboxetine but less SSRI-type events such as diarrhoea carries a warning with regard to its use in and nausea (17,18). patients with a history of epilepsy. Table 1: Placebo-controlled trials – incidence (%) of The possibility for a switch to adverse effects (17,18) mania/hypomania exists, especially in patients SIDE REBOXETINE PLACEBO with bipolar disorder. A literature report (16) EFFECT describes the emergence of hypomanic Dry mouth 27 16 symptoms in 3 bipolar patients within 2-4 Constipation 17 8 Increased 14 7 weeks of starting reboxetine. sweating A review of the tolerability of reboxetine Insomnia 14 5 states that symptoms related to hypotension or Urinary 52 tachycardia may be experienced by up to 10% hesitancy of patients who receive the drug. It should be Impotence 5 0 used with caution and close supervision in Tachycardia 5 2 patients with cardiac disease and/or taking Sexual dysfunction appears to be dose-related antihypertensives(17). Orthostatic hypotension (doses of >8mg). Urinary hesitation/retention is more common at doses higher than the occurred more frequently in males than maximum recommended. females in long-term studies. It may be Graylands Hospital Drug Bulletin 2002 Vol 10 No 3 November - 2 – Reboxetine is not on the hospital formulary as yet. advisable to avoid reboxetine in men with nefazodone/fluvoxamine and fluoxetine (due prostatic enlargement (17). to CYP3A4 inhibition and a long elimination Short and long term studies in the elderly and half-life respectively). adults showed that reboxetine treatment Switching from reboxetine: At least a week’s induced rhythm abnormalities more drug-free interval should be allowed before frequently than imipramine and placebo MAOIs (and possibly moclobemide) are (sinus tachycardia being the most frequently commenced. observed abnormality)(19,20). Reboxetine was Combination with other antidepressants also associated with occasional atrial and Reboxetine has been used in combination ventricular ectopic beats in the elderly. with SSRIs(17,23,24) and mirtazapine (17) to treat Treatment emergent conduction abnormalities resistant depression with some success. It in the elderly were mostly left anterior may be favoured over TCAs as a hemiblock. noradrenergic agent due to reduced potential A study by the manufacturer to examine the for drug interaction and better tolerability. effect of reboxetine on cardiac repolarisation Combination strategies are not in 20 healthy subjects, found no statistically recommended and should only be significant prolongation of the QTc interval, undertaken with caution and when other at exposures of up to twice the recommended treatment options have failed. dose (21). Drug Interactions A case report of hyponatremia in association Compounds that inhibit CYP3A4 may with reboxetine (occurred again upon increase the plasma levels of reboxetine. rechallenge) has been published (22). These include ketoconazole, itraconazole, clarithromycin, erythromycin, fluvoxamine Dosage and administration nefazodone and cimetidine. Carbamazepine Recommended starting dose is the therapeutic may induce the metabolism of reboxetine, dose: 4mg twice daily, increasing to 10mg resulting in lower plasma levels. The doses of daily if necessary after 3 weeks. reboxetine may need to be adjusted Elderly: 2mg twice daily, increased to 6mg accordingly. Reboxetine appears to have little daily if necessary after 3 weeks. effect on the activity of other major Renal/hepatic impairment: start at 2mg twice isoenzymes. daily and increase according to patient tolerance. The use of reboxetine and lithium has not been specifically evaluated. Due to minimal Switching to and from reboxetine glomerular filtration of unbound reboxetine, No specific data regarding this issue could be no effect on lithium elimination is expected. found. The following are recommendations However, the manufacturers recommend only. monitoring of the lithium level. Switching to reboxetine: A 14 day drug-free gap is required when switching from MAOIs. Use with ergot derivatives (in some migraine With other agents, a careful cross-taper may preparations) may result in increased