Prolonged anticholinergic delirium following antihistamine overdose.

OBJECTIVE

A case of anticholinergic delirium in a female adolescent is described, exploring the pharmacokinetic reasons for the prolonged time course and reviewing the management provided.

CONCLUSION

A 14 year old female hospitalised for depression ingested large quantities of promethazine and cyproheptadine. A severe anticholinergic delirium ensued which resolved after six days, much longer than the expected duration. The likely cause of the prolonged delirium was the interaction of promethazine and fluvoxamine through the inhibition of the CYP2D6 enzyme. The patient's young age, the severity of the poisoning and the use of drugs with anticholinergic properties to manage the delirium may also have contributed. The delirium may have been reversed had a cholinesterase inhibitor been provided soon after the overdose.