Do you know about donepezil and succinylcholine?

A recent drug advertisement for donepezil hydrochloride, marketed as Aricept in the medical press, aroused our interest. It stated that: ‘Aricept may have possible synergistic activity with succinylcholine- type muscle relaxants’. Aricept is indicated for the symptomatic treatment of mild to moderately severe Alzheimer's dementia [1]. It is a reversible, non-competitive inhibitor of acetyl cholinesterase, the predominant cholinesterase in the brain. In vitro, it is over 1000 times more potent an inhibitor of this enzyme than of butyryl cholinesterase, an enzyme which is present mainly outside the central nervous system [2]. Research of the literature only identified a letter in 1997 [3] highlighting the possible interaction of donepezil and succinylcholine. We were interested in determining whether the knowledge of possible interaction of Aricept and succinylcholine was known in our anaesthetic department. Questionnaires were sent out to all departmental members (40) and from a 74% response rate, no one was aware of this possible interaction. We were not surprised at this result, and feel that this possible interaction is important and should be better publicised to anaesthetists. Just over 385 000 people in the UK suffer from Alzheimer's disease (data from Alzheimer's Society). Elsai Limited have recommended (even though no formal studies have been done) if a patient requires succinylcholine-type neuromuscular blockade during surgery, the patient should be withdrawn from Aricept therapy 2–3 weeks prior to the operation. The terminal disposition half-life is approximately 70 h [4] and steady state is achieved within 3 weeks after initiation of therapy [4]. In emergency procedures where neuromuscular blockade is required, the anaesthetist should be aware of the potential for prolonged muscle relaxation.