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ANTI- PARKINSONISM Dr: Samah Gaafar Al-shaygi
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Neurodegenerative diseases. Dopamenergic neurones in substantia nigra. Environmental* genetic factors. Resting tremor, muscular rgidity & bradykinesia. Secondary parkinsonism.
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Therapy aim is to minimize disability and side effects while maintaining quality of life. restore dopamine in the basal ganglia & antagonize ACH. The drugs are almost palliative ones.
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1. Levodopa & Carpidopa. L-dopa is a dopamine precursor. Very effective in the beginning of the dx. Carpidopa a dopa decarboxylase inhibitor. 1. Decrease the dose of L-dopa needed (*4-5). 2. Decrease side effects.
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Absorption & metabolism: On empty stomach 45min before a meal. L-dopa is rapidly absorbed from the GIT. is absorbed primarily in the proximal duodenum by a saturable large neutral amino acid (LNAA) transport system. (Competition) Has short ½ life (1-2hrs). not bound to plasma proteins. It crosses the blood-brain barrier by saturable facilitated diffusion and competes with LNAA for transport into the brain.
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ADVERSE EEFECTS: 1. Peripheral effects: N&V. Tachycardia & hypotension. Mydriasis. Brownish urine & saliva. 2. CNS: anxiety, psychosis, depression. 3. Wearing off. 4. Dyskinesias and dystonias.
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Selegiline: MAO-B inhibitor. Lipophilic. Reduces L-dopa dose. Metabolized to amphetamine (insomnia). COMT-inhibitors: L-dopa COMT 3-O-methyl dopa (competes with L-dopa for brain transport). Entacapone reduces wearing off phenomena.
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Pharmacokinetics: Plasma protein bound >98%. Metabolized & excreted hepatically & renally. Adverse effects: Diarrhea, postural hypotension, sleep disorders. Fulminant hepatic necrosis (tolcapone).
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Dopamine-receptor agonists: In advanced dx with motor fluctuation & dyskinesia. Have no effects on non-responders to L-dopa. Bromocreptine.more nausea, hallucinations & less dyskinesias. Worsen MI, perepheral vascular dx, pulmonary fibrosis. Apomorphine as injections in advanced dx. Delay the need for L-dopa in early parkinson & decrease the L-dopa dose in advanced dx. No worsening of vasospasm & no fibrosis.
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Amanitidine: An anti-viral drug. Increases the release of dopamine & blocks the cholinergic receptors. Less effective than L-dopa & readily developed tolerance. Restlessness, hallucinations, toxic psychosis. Little effect on tremor butmore the anticholinergic on rigidity & bradykinesia.
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Antimuscarinic agents: Only adjuvant role. Benztropin, procyclidine. S.E: mood changes, xerostomia, urinary retention tachycardia. Contraindicated in glucoma, BPH & pyloric stenosis.
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Thank you
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