MYASTHENIA GRAVIS

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DRUGS USED IN MYASTHENIA GRAVIS:

DRUGS USED IN MYASTHENIA GRAVIS ZEENATH BANU ASSISTANT PROFESSOR DEPARTMENT OF PHARMACOLOGY

MYASTHENIA GRAVIS:

MYASTHENIA GRAVIS Myasthenia gravis is an autoimmune disorder affecting about 1 in 10,000 population, due to development of antibodies directed to the nicotinic receptors (NR) at the muscle endplate Reduction in number of free NM cholinoceptors to 1/3 of normal or less Structural damage to the neuromuscular junction. Results in weakness and easy fatigability on repeated activity, with recovery after rest. HALLMARKS OF MG Eye lid drooping (ptosis) Impaired speech (dysarthria) Difficulty Swallowing(dysphagia) Double Vision (diplopia) Weakness of all extremities Easily fatigued

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TREATMENT Acetylcholinesterase inhibitors- Neostigmin , Pyridostigmine Corticosteroids- --Prednisolone, Cyclosporine Plasma exchange Intravenous immunoglobulin Thymectomy 1.Acetylcholinesterase inhibitors- Neostigmine: Improve muscle contraction by allowing ACh released from prejunctional endings to accumulate and act on the receptors over a larger area, as well as by directly depolarizing the endplate. Dose : 15 mg orally 6 hourly. Pyridostigmine : An alternative which needs less frequent dosing. If intolerable muscarinic side effects are produced, atropine can be added to block them.

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2.Corticosteroids- They inhibit production of NR-antibodies and may increase synthesis of NRs. Prednisolone 30–60 mg/day induces remission in about 80% of the advanced cases. Both azathioprine and cyclosporine also inhibit NR-antibody synthesis by affecting T-cells, but response to the former is slow in onset (takes upto 1 year), while that to the latter is relatively quick (in 1–2 months). 3.Plasma exchange Removal of antibodies by plasmapheresis (plasma exchange) is another therapeutic approach. 4. Thymectomy Thymectomy is effective in a majority of the cases. It produces gradual improvement and even complete remission has been obtained. Thymus may contain modified muscle cells with NRs on their surface, which may be the source of the antigen for production of anti-NR antibodies in myasthenic patients

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Overtreatment with anti- ChEs If the dose of the antiChE is not adjusted according to the fluctuating requirement, relative overdose may occur from time-to-time. Overdose also produces weakness by causing persistent depolarization of muscle endplate, and is called cholinergic weakness . The two types of weakness require opposite treatments. They can be differentiated by edrophonium test DIAGNOSTIC METHODS AMELIORATIVE TEST:- EDROPHONIUM i.v. PROVOCATIVE TEST:- d- tubocurarine DEMONSTRATION OF ANTI- NICOTINIC RECEPTOR ANTIBODIES IN PLASMA —

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