Which of the following medications is NOT readily used for MG treatment or diagnosis?

Echothiophate is not commonly used for the treatment or diagnosis of Myasthenia Gravis (MG). This medication is an irreversible acetylcholinesterase inhibitor primarily indicated for glaucoma treatment because of its effect on increasing the availability of acetylcholine at the neuromuscular junction. While it does increase acetylcholine levels similarly to other drugs used for MG, its long duration of action and potential side effects make it less favorable for diagnosing or managing MG.

In contrast, the other medications listed—edrophonium, neostigmine, and pyridostigmine—are specifically designed for the treatment and diagnosis of MG. Edrophonium is often used in the Tensilon test to confirm a diagnosis of MG due to its rapid action. Neostigmine and pyridostigmine are both utilized for their longer-term management of symptoms associated with MG, helping to relieve muscle weakness by inhibiting acetylcholinesterase and allowing more acetylcholine to be available at the neuromuscular junction. Thus, echothiophate's primary application in glaucoma treatment rather than in MG underscores why it is not readily used for that condition.