Quetiapine is used in the treatment of delirium but recently there have been case reports of delirium associated with quetiapine especially with overdose. We present a case of delirium probably caused by quetiapine.

45 years-old male, with a diagnoses of Bipolar Disorder for 25 years and treated with lithuril 900mg/d, admitted to our outpatient clinic for starting insomnia during the last week. Quetiapine 100mg/d at night dosage added to medication but he ingested 200mg/d with the fear of that if he couldn't sleep. 2 hours later the symptoms of delirium started and continued for six hours and recovered with no treatment. The lithuril level was in normal ranges. Other psychotic and organic disorders were ruled out. It is learned that his brother had delirium with Quetiapine so he was thought to be a poor (deficient) metabolizer and Quetipine decreased to 25 mg/day in the night dosage but he had a delirium state with the same features again. Next morning he admitted to outpatient clinic only with hippomanic symptoms but no symptom of delirium. Quetiapine was discontinued and lithuril was combined with another atypical antipsychotic and symptoms were remitted.

To our knowledge this is the first case of delirium induced with low dosage of quetiapine. There were no organic risk factors or drug interactions. While a correlation of dosage and effect could be shown with Quetiapin, this case emphasizes that inter- and intraindividual differences could be observed probably due to genetical influence. Drug monitoring therefore seems useful in clinical setting.