Re‐administration of mirtazapine could overcome previous mirtazapine‐ associated restless legs syndrome?

Abstract

Mirtazapine (MIR) has been proved to be effective and tolerable in the treatment of depression with its unique pharmacological profiles, by blockades of the postsynaptic 5-HT2 and 5-HT3 receptors and presynaptic α2-autoreceptor, and by stimulating postsynaptic 5-HT1 receptor.1 Recently, several reports,2, 3 including our group,4 have presented MIR-associated restless legs syndrome (RLS) characterized by unpleasant aching sensation of both legs with creeping and crawling feelings, of which the pathophysiology is unclear but mainly supposed to be related to dysfunction of the dopamine pathway and presented mostly by serotonergic-stimulating agents.5 Interestingly, we experienced two cases that did not show MIR-associated RLS after re-administration of MIR, though they suffered RLS at the first administration of the drug. As reported previously,4 a 56-year-old Korean female patient with a diagnosis of major depressive disorder, according to the 4th edition of the Diagnostic and Statistical Manual (DSM-IV), showed RLS after MIR treatment on the 5th day of MIR administration and recovered 4 days after stopping MIR. She was not found to have any laboratory abnormalities and underlying medical causes might be predisposed to RLS, thus, MIR was switched to paroxetine of 20 mg/day. She had not visited the outpatient clinic after discharge for 7 months. She revisited the outpatient clinic for depressed mood, loss of energy, and suicide ideation and so was given paroxetine of 20 mg/day in the first place, showing no response in depressive symptoms, especially insomnia. MIR was reapplied and effectively worked, improving her depressive symptoms including insomnia without RLS. A 58-year-old female with a DSM-IV diagnosis of major depressive disorder, visited the outpatient clinic of Kangnam St. Mary's Hospital. She complained of severe insomnia, anxiety, agitation and loss of volition. All laboratory screenings for her medical condition showed no definite abnormality and she was given MIR of 15 mg/day and it was increased to 30 mg/day on day five. She reported RLS symptoms such as deep creeping sensation in both legs upon falling asleep, which was aggravated at night. Further evaluation for RLS showed no evidence of any medical illness. MIR was switch to tianeptine of 50 mg/day as clonazepam of 1 mg/day for 5 days was not effective. She was maintained with the same dose of tianeptine for about 2 months, showing moderate improvement of depressive symptoms. However, there was no follow-up visit since then. At 4 months later, she revisited the outpatient clinic due to recurred depression related to familial conflict, and insomnia was her main complaint. MIR of 15 mg/day was re-administered to her and increased to 30 mg/day on day eight, MIR successfully treated her depressive symptoms without RLS. This report led us to speculate on how these two patients could escape from MIR-associated RLS that they had previously experienced, with using the same dosing schedule. As is well known, the complicated role of noradrenergic and serotonergic transmission would be contributed to the pathogenesis of the RLS, although the equivocally suggested pathophysiology of RLS is a dysfunction of the subcortical central nervous system, mainly via the dopamine pathway.5 This unclear pathophysiology makes us not preclude the exact mechanism of the findings of this report. We might suppose: previous MIR administration would alter the suggested 5-HT and noradrenergic neurotransmission system including receptor sensitivity, past experience may affect the individual sensitivity to RLS, and finally, although it is very coincidental, spontaneous resolution of an undetected causative factor at a past medical examination. In conclusion, this report may suggest that MIR would be an exploratory model of RLS as a pharmacological approach in the etiopathogenesis of RLS3 and further studies on the role of MIR in the development of RLS could be launched.