Week 4 notes 12 - TreatmentofParkinsons In essence,...

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Treatment of Parkinson’s In essence, Parkinson's Disease is a spontaneous degeneration of the dopamine- producing cells in the mid-brain. The neurotransmitter dopamine is an inhibitory neurotransmitter at this location in the brain and its job is to inhibit the firing of certain nerve cells that are involved with skeletal muscle contraction. In the state of health, this is the mechanism by which skeletal muscles can relax, (i.e., it reduces the state of skeletal muscle tone). In patients with Parkinson's Disease, there is a deficiency of dopamine and this relaxation function is impaired. The stimulatory skeletal muscle function in Parkinson's patients, however, remains intact. This muscle contraction function is activated by the neurotransmitter acetylcholine. Because of the relative deficiency of dopamine in the brain compared to the amount of acetylcholine, there is an imbalance between the contractile and relaxation functions of the skeletal muscle innervation with skeletal muscle contraction predominating. This gives rise to the skeletal muscle rigidity that is the typical manifestation of Parkinson's Disease. Categories of drugs that are effective in relieving symptoms of Parkinson's Disease are the Dopamine Agonists, Anticholinergics, Monoamine Oxidase B Inhibitors, and COMT Inhibitors. List of Available Dopamine Agonists Used for Parkinson's Disease levodopa-carbidopa (Sinemet) bromocryptine (Parlodel) amantadine (Symmetrel) pergolide (Permax) pramipexole (Mirapex) ropinirole (Requip) Pharmacodynamics of the Dopamine Agonists The pharmacodynamics of the dopamine agonist drugs in Parkinson's Disease is to replace the natural deficiency of the inhibitory neurotransmitter dopamine and attempt to reestablish the balance between the contraction and relaxation functions of the brain on skeletal muscle. Pharmacokinetics of the Dopamine Agonists All of the dopamine agonists are well absorbed orally. All are metabolized in the liver except amantadine, which is not metabolized at all. Levodopa is also metabolized to some extent in the G.I. tract. All of the agents are excreted in the urine as metabolites or as parent drug. Advantages of the Dopamine Agonists in the Treatment of Parkinson's Disease GENERAL ADVANTAGES OF THE DOPAMINE AGONISTS 1
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Treatment of Parkinson’s - All are available orally - They mimic the actions of the natural inhibitory neurotransmitter, dopamine; they actually replace in the brain what the brain is lacking which comes close to a specific correction of the basic pathophysiology. - Rapid onset of action; usually 10-15 min.; bromocriptine may take longer. - Long duration of action; 12-24 hrs. - Some useful as monotherapy; single drug regimens enhance and simplify compliance ADVANTAGES OF SPECIFIC DOPAMINE AGONIST DRUGS LEVODOPA-CARBIDOPA - Levodopa is metabolized into dopamine; carbidopa blocks an enzyme responsible for the peripheral (non-brain) metabolism of levodopa and allows more of the levodopa to enter brain where it is needed. - Available in sustained-release formulation (Sinemet CR); allows BID dosing
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Week 4 notes 12 - TreatmentofParkinsons In essence,...

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