What is the medication administered to a symptomatic patient to diagnose myasthenia gravis?

The correct medication used to diagnose myasthenia gravis in a symptomatic patient is edrophonium. This drug is a short-acting acetylcholinesterase inhibitor that temporarily increases levels of acetylcholine at the neuromuscular junction. When administered to a patient with myasthenia gravis, edrophonium often leads to a rapid and marked improvement in muscle strength, which serves as a confirmatory response for the diagnosis.

This action is particularly useful during a diagnostic test known as the edrophonium test or Tensilon test. In this setting, the patient's muscle weakness due to myasthenia gravis temporarily improves with the administration of edrophonium, helping to differentiate it from other conditions that may cause similar symptoms.

While other medications such as pyridostigmine and neostigmine are used in the chronic management of myasthenia gravis, they are not typically used for diagnostic purposes. Donepezil is primarily indicated for Alzheimer's disease and is not relevant to diagnosing myasthenia gravis. Thus, edrophonium's specific role in producing a rapid improvement in symptoms directly supports its use as a diagnostic tool for this neuromuscular disorder.