Levodopa


Thông tin thuốc gốc
Chỉ định và Liều dùng
Oral
Parkinsonism
Adult: Initially, 125 mg bid; increase gradually every 3-7 days according to response. Max dose: 8 g daily in divided doses.

Oral
Parkinsonism in conjunction with carbidopa
Adult: Patients not previously on levodopa therapy: Initially, 25 mg carbidopa with 100 mg levodopa tid; gradually increase in increments of 12.5 mg carbidopa with 50 mg levodopa or 25 mg carbidopa with 100 mg levodopa every day or on alternate days. Maintenance dose: 75-200 mg carbidopa with 750 mg to 2 g levodopa daily in divided doses. Max carbidopa dose: 200 mg daily. Patients previously on levodopa monotherapy: 20-25% of the dose previously taken 3 or 4 times daily. Patient previously on other levodopa/dopa-decarboxylase combination therapy: Initial dose should provide the same daily levodopa dose.

Oral
Parkinsonism in conjunction with benserazide
Adult: Patients not previously on levodopa therapy: Initially, 50 mg 3 or 4 times daily; gradually increase in increments of 100 mg once or twice wkly. Increase initial dose to 100 mg tid for advanced disease stages. Maintenance dose: 400-800 mg daily in divided doses; most require <600 mg daily. Patients previously on levodopa monotherapy: 10-15% of the usual dose previously taken. Patient previously on other levodopa/dopa-decarboxylase combination therapy: Initially, 50 mg 3 or 4 times daily.
Elderly: Initially, 50 mg once or bid, then increase by 50 mg every 3rd or 4th day.
Cách dùng
Should be taken with food. May be taken w/ meals to reduce GI discomfort. Keep a consistent diet.
Chống chỉ định
Angle-closure glaucoma; malignant melanoma.
Thận trọng
Heart disease, liver or renal disease, pulmonary disease, endocrine disorders, seizure disorders, dementia or psychosis; open-angle glaucoma, osteomalacia, history of peptic ulcer. Monitor hepatic, psychiatric, haematological, renal and CV functions periodically. May impair ability to drive or operate machinery. Elderly. Avoid abrupt withdrawal. Pregnancy and lactation.
Phản ứng phụ
GI disturbances e.g. nausea, vomiting, anorexia. GI bleeding in peptic ulcer patients. Orthostatic hypotension, cardiac arrhythmias. Psychiatric symptoms (especially the elderly), depression with or without suicidal tendency. Abnormal involuntary movements or dyskinesias, delirium, hallucinations. Slight elevation of liver enzymes, BUN and uric acid. Transient leucopenia and thrombocytopenia.
Gastroenteral/PO: C (FDA pregnancy category C if used in combination therapy w/ carbidopa.)
Quá liều
Symptoms: Hypertension (initially), hypotension, sinus tachycardia, symptomatic orthostatic hypotension, marked confusion, agitation, insomnia, restlessness, severe anorexia, insomnia.
Tương tác
Increased postural hypotension and possible reduced absorption with TCAs. Reduced effects with phenothiazines, butyrophenones, thioxanthenes and other antipsychotic agents; reserpine, papaverine, phenytoin, isoniazid. Reversal of effects of levodopa monotherapy with pyridoxine. Exacerbation of abnormal involuntary movements and possibly delayed absorption with anticholinergics. Additive hypotensive effects with antihypertensive agents. Increased CNS toxicity with methyldopa. Exacerbation of parkinsonian symptoms with metoclopramide.
Potentially Fatal: Increased risk of hypertensive crises with nonselective MAOIs. Increased risk of cardiac arrhythmias with cyclopropane or halogenated anaesthetics.
Food Interaction
Food reduces and delays absorption of levodopa. Effects of levodopa reduced by beans, liver, skimmed milk, yeast and wheat germ. Large neutral amino acids reduce absorption and passage across blood-brain barrier. Recommended to be taken after a light meal to slow absorption and reduce central emetic effect.
Lab Interference
False-positive Coombs' test. Interferes with serum tests for bilirubin, catecholamines, creatinine, glucose and uric acid and urine tests for creatinine, glucose, ketone and vanillyl mandelic acid (VMA).
Tác dụng
Description: Levodopa increases dopamine levels in the brain leading to the stimulation of dopamine receptors.
Pharmacokinetics:
Absorption: Rapidly absorbed from the GI tract (oral); absorption reduced and delayed by food. Peak plasma concentrations within 2 hr.
Distribution: Protein-binding: 10-30%. Penetrates the blood-brain barrier; crosses the placenta; distributed into breast milk.
Metabolism: Metabolised in the gut, liver and kidney; decarboxylated by L-aminodecarboxylase to dihydrophenylacetic acid (DOPAC) and homovanillic acid (HVA). Other routes: O-methylation, transamination, oxidation.
Excretion: Via urine within 24 hr (80% as metabolites); via faeces (minimal amounts). 30-60 min (elimination half-life).
Bảo quản
Store at 20-25°C (68-77°F).
Phân loại MIMS
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