The mechanism of antidepressant action of quetiapine is unclear. However, it has been suggested that its antidepressant activity is mediated by its metabolite N-Desalkylquetiapine, which leads to norepinephrine reuptake transporter inhibition and partial serotonin 1A agonism.4 A speculation may be that slow clearance of the metabolites as an age effect or genetic trait in this case led to very high levels of N-Desalkylquetiapine potentiating quetiapine's antidepressant effect and leading to worsening of mania. Moreover, a positron emission tomography (PET) study using quetiapine 750 mg or 450 mg/day found that there was no D2 receptor occupancy at the low dose of quetiapine, while 5HT2A receptor occupancy was consistently high.5 Despite the normal head CT scan, brain-aging related neurotransmitter changes and therefore different medication effects could be considered. Calabrese et al.1 reported an incidence of treatment-emergent mania 2.2% with 600 mg/day of quetiapine and 3.9% with 300 mg/day of quetiapine. The absence of dopaminergic receptors blockade and the high affinity for serotonergic receptors at lower doses, may explain quetiapine's antidepressant activity and worsening mania in case of slow titration in manic patients. In this case, geriatrician treatment practice of "start low and go slow" raised questions.
Worsening Mania Associated With Slow Increase of Quetiapine Dose
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