Abstract
Data on quetiapine overdose are sparse in the literature [1]. Most of these limit the neurological and mental state symptoms of overdose to sedation, drowsiness and loss of consciousness [2]. Few sources report delirium as a likely consequence of overdoses with quetiapine alone.
Quetiapine is an atypical antipsychotic used in the management of schizophrenia and bipolar I disorder, and is used off-label for a variety of other purposes, including insomnia, anxiety and personality disorders. The antipsychotic effect of quetiapine is thought to be mediated through the antagonist activity at the dopamine (D1 and D2) and serotonin (5HT-1 and 5 HT-2) receptors. In addition, quetiapine has an antagonistic effect on the histamine H1 receptor. This is thought to be responsible for the sedative effect of the drug. Other than sedation, quetiapine is a popular drug because of its relatively benign side-effect profile with regard to extra-pyramidal symptoms and serum prolactin level elevation.
Reported here is the case of a 23-year-old woman who presented to Emergency Services 3 h after the ingestion of 12 g of quetiapine in a suicide attempt. The patient reported visual hallucinations, increasing agitation and confusion following the ingestion. There was no evidence of concomitant use of any other drugs, illicit or prescribed. The patient was initially sedated but became progressively more agitated and satisfied criteria for the diagnosis of delirium as evidenced by disorientation, impaired concentration and attention, visual and auditory hallucination. This was initially misdiagnosed and control of agitation was attempted with i.m. benzodiazepines and olanzapine (15 mg) with resultant worsening of mental state and confusion. All antipsychotic medication was subsequently withheld and behavioural disturbance was managed conservatively with rapid resolution of mental state. Retrospectively the patient was able to give a history corroborating the temporal correlation between the overdose and the onset of delirium.
Investigations including a complete blood exam, biochemical analysis, urine drug screen, blood alcohol and paracetamol levels were all unremarkable. Her mental state improved before neuroimaging could be done and the patient continued to maintain improvement, pre-empting the need for the same. In keeping with the vascular side-effects of quetiapine the present patient experienced tachycardia, hypotension and some QTc prolongation, which resolved with supportive management [3].
A detailed literature review indicated only one case series of 45 patients with quetiapine overdose that documented delirium as a side-effect in three of those patients [3]. Delirium is an uncommon central nervous manifestation of quetiapine overdose, and agitation secondary to this is likely to be misinterpreted as psychotic agitation. Awareness of delirium as a possible side-effect is likely to inform appropriate management.
Changes in sensorium have been documented with quetiapine-related neuroleptic malignant syndrome [4] and in combination with other medication likely to precipitate a serotonergic syndrome [5]. To the best of the author's knowledge this is only the second report documenting quetiapine-induced delirium.