Tiêu đề 14. DRUGS USED IN MYASTHENIA GRAVIS.pdf ✅

PHARMD GURU Page 1 ETIOLOGY AND SYMPTOMS: Myasthenia gravis is an acquired auto-immune disorder causing fatigue and weakness of skeletal muscles. The disease is associated with production of IgG type of antibodies to ACh receptors (NM) at the post-junctional motor end plate. In 90% of patients having this disease, anti-ACh antibody titre is raised. Reduction in number of NM receptors results in reduction in amplitude of the end plate potential which in turn fails to trigger an action potential. The symptoms include weakness of muscle and fatigue which worsens after excersice but goes off after rest. The weakness in muscles is not associated with pain. In early stages of disease, the fast moving muscles are affected first. Hence, symptoms start with ptosis, diplopia, slurring of speech, difficulty in swallowing and weakness of extremities. Subsequently, all muscles are progressively affected including respiratory muscles. The thymus shows abnormality in about 75% cases of myasthenia gravis. TREATMENT OF MYASTHENIA GRAVIS:  Any reversible anti-AChE drug of intermediate duration of action is useful for treatment of myasthenia gravis. Initially, the doses are given on an empirical basis but later titrated for prolonged therapy.  Initially Neostigmine is given in a oral dose of 15-30 mg/day in divided doses or 0.5-2.5 mg as intramuscular or sub-cutaneous injection with gradual increment till therapeutic goals are achieved. Alternatively oral Pyridostigmine 60 mg three times a day is followed by gradual increase till satisfactory response. Another alternative is oral Ambenonium 2.5-5 mg, every 6 hours.  Sustained release preparations of Pyridostigmine are also available, which can be given at bed time. Longer acting AChE inihibitors like organophosphates are not used.  During prolonged therapy, titration of the dose is done. The patient’s condition may swing between myasthenia gravis (due to lower doses of drugs) or cholinergic crisis (due to toxicity of drugs). Both the conditions can end up in to muscular weakness. In such cases, doses of anti-AChE drug need to be adjusted. Prior to DRUGS USED IN MYASTHENIA GRAVIS