An intravenous preparation of pyridostigmine (1 mg IV equivalent to 30 mg PO) may be considered in selected settings where intravenous immunoglobulin or plasma exchanges are unavailable, but caution is needed as there may be an increased risk of cardiac arrythmia. It is suggested to discontinue AChE inhibitors in patients with MG crisis requiring mechanical ventilation support, due to concerns of increased bronchial secretion and bronchospasm, with a goal of restarting them during the waning process or after extubation. A sustained-release form of pyridostigmine (Mestinon Timespan 180 mg) at nighttime may be useful for patient with weakness upon awakening. It has an onset of action as early as 15–30 min with a duration of about 3–4 h. It is usually given at an initial dose of 30–60 mg every 4–6 h and may be increased to 90–120 mg every 4–6 h based on patient response and tolerance. Oral pyridostigmine has been the most widely used preparation since the 1950s among other AChE inhibitors due to its longer duration of action, better tolerance profile, and fewer cholinergic side effects. Clinical response to AChE inhibitors may vary between individuals or the muscles involved for example, patients with ocular MG may have better alleviation of the ptosis than diplopia. AChE inhibitors have remained the standard management for MG since early observations of dramatic response of these drugs (physostigmine, neostigmine) in the mid-1930s. They work by reversibly inhibiting the action of AChE, preventing the breakdown of acetylcholine (ACh) and, thus, increasing the amount of ACh available at the neuromuscular junction (NMJ) to bind to postsynaptic ACh receptors. Peripherally acting AChE inhibitors are used as symptomatic treatments for temporarily alleviating muscle weakness in MG patients. On the other hand, as MG is usually a chronic disease, side effects of exposure to chronic use of steroids or other immunosuppressants may dramatically affect the lifespan or quality of life.Ģ.1. Therefore, more aggressive approaches such as “rebooting” of the immune system with high-dose cyclophosphamide or autologous bone marrow transplantation were used in some refractory cases with life-threatening disease. Treatment of MG remains challenging as a subgroup of patients are treatment refractory, therefore having recurrent hospitalizations for MG crisis, requiring maintenance IVIG or PLEX. These treatments along with the availability of antibiotics and advanced respiratory care have led to substantial improvement in quality of life and a mortality rate of 5–9%. Corticosteroid treatment for MG was introduced in the 1960s followed by the use of azathioprine, plasma exchange (PLEX) and intravenous immunoglobulin (IVIG). Thymectomy was introduced in 1939 and its role in MG pathogenesis was later demonstrated, but its effect in MG was not confirmed through a randomized clinical trial until decades later. The discovery of anticholinesterase (AChE) inhibitors resulted in improved diagnostic accuracy and also decreased mortality, which was estimated at 32% in 6 years in 1953. Prior to the introduction of acetylcholinesterase inhibitors in 1934, patients diagnosed with MG had a grave prognosis and many succumbed to respiratory failure and pneumonia in 1–2 years. Myasthenia gravis (MG) is a an acquired, autoimmune disease of the neuromuscular junction which is caused by autoantibodies against different components of the neuromuscular junction.
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