The black swan theory describes rare events beyond the realm of normal expectation. We use ketamine on a daily basis, but are there any circumstances in which ketamine simply will NOT work?
This interesting case report by an Ex-Sydney HEMS physician Daniel Kornhall describes how ketamine failed completely as an anaesthetic agent in a psychiatric patient with a toxic lamotrigine overdose.
Lamotrigine, as we all obviously know, exerts its antiepileptic effect by inhibiting presynaptic sodium channels thus reducing the release of the excitatory glutamate and stabilising excitable neuronal membranes. Ketamine’s dissociative anaesthetic effects are a bit more of a mystery and diverse, but they are thought to involve increasing glutamate release through non-NMDA receptor pathways. It therefore follows, that if one drug prevents the release of glutamate and second drugs effects depend on its release, the second drug will not work.
With our high volume of ketamine use, incidents such as this are worth bearing in mind the next time you see a patient with a mixed polypharmacy overdose.
Lamotrigine is therefore ketamine’s black swan.