Edrophonium (Tensilon®) is a short-acting anticholinesterase which can be administered intravenously. In myasthenia gravis a transient improvement in muscle strength occurs within 30 s of the administration of 4 to 8 mg of edrophonium. The effect only lasts for about 60 s. A positive response may not be seen in a myasthenic patient treated with anticholinesterase drugs if the patient is in a cholinergic state. In fact such a patient can be made considerably worse by the test. A patient on anticholinesterase therapy should be pretreated with intravenous atropine first to prevent a bradycardia, and resuscitation facilities should be available when performing the test.
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