Levodopa
Levodopa (Dopar, Larodopa, L-Dopa)
Levodopa
(lee-voh-DOH-pah) Dopar Larodopa L-Dopa (Rx)

Classification: Antiparkinson agent

Action/Kinetics: Depletion of dopamine in the striatum of the brain is thought to cause the symptoms of Parkinson's disease. Levodopa, a dopamine precursor, is able to cross the blood-brain barrier to enter the CNS. It is decarboxylated to dopamine in the basal ganglia, thus replenishing depleted dopamine stores. Peak plasma levels: 0.5-2 hr (may be delayed if ingested with food). t1/2, plasma: 1-3 hr. Onset: 2-3 weeks, although some clients may require up to 6 months. Extensively metabolized both in the GI tract and the liver; metabolites are excreted in the urine.

Uses: Idiopathic, arteriosclerotic, or postencephalitic parkinsonism due to carbon monoxide or manganese intoxication and in the elderly associated with cerebral arteriosclerosis. Levodopa only provides symptomatic relief and does not alter the course of the disease. When effective, it relieves rigidity, bradykinesia, tremors, dysphagia, seborrhea, sialorrhea, and postural instability. Used in combination with carbidopa. Investigational: Pain from herpes zoster; restless legs syndrome.

Contraindications: Concomitant use with MAO inhibitors, except MAO-B inhibitors (e.g., selegiline). History of melanoma or in clients with undiagnosed skin lesions. Lactation. Hypersensitivity to drug, narrow-angle glaucoma, blood dyscrasias, hypertension, coronary sclerosis.

Special Concerns: Use with extreme caution in clients with history of MIs, convulsions, arrhythmias, bronchial asthma, emphysema, active peptic ulcer, psychosis or neurosis, wide-angle glaucoma, and renal, hepatic, or endocrine diseases. Use during pregnancy only if benefits clearly outweigh risks. Safety has not been established in children less than 12 years of age. Geriatric clients may require a lower dose as they have a reduced tolerance for the drug and its side effects (including cardiac effects). Clients may experience an ``on-off'' phenomenon in which they experience an improved clinical status followed by loss of therapeutic effect.

Side Effects: The side effects of levodopa are numerous and usually dose related. Some may abate with usage. CNS: Choreiform and/or dystonic movements, paranoid ideation, psychotic episodes, depression (with possibility of suicidal tendencies) dementia, seizures (rare) dizziness, headache, faintness, confusion, insomnia, nightmares, hallucinations, delusions, agitation, anxiety, malaise, fatigue, euphoria. GI: N&V;, anorexia, abdominal pain, dry mouth, sialorrhea, dysphagia, dysgeusia, hiccups, diarrhea, constipation, burning sensation of tongue, bitter taste, flatulence, weight gain or loss, GI bleeding (rare), duodenal ulcer (rare). CV: Cardiac irregularities, palpitations, orthostatic hypotension, hypertension, phlebitis, hot flashes. Ophthalmologic: Diplopia, dilated pupils, blurred vision, development of Horner's syndrome, oculogyric crisis. Hematologic: Hemolytic anemia, agranulocytosis leukopenia. Musculoskeletal: Muscle twitching (early sign of overdose), tonic contraction of the muscles of mastication, increased hand tremor, ataxia. Miscellaneous: Blepharospasm (early sign of overdose), urinary retention, urinary incontinence, increased sweating, unusual breathing patterns, weakness, numbness, bruxism, alopecia, priapism, hoarseness, edema, dark sweat and/or urine, flushing, skin rash, sense of stimulation. Levodopa interacts with many other drugs (see what follows) and must be administered cautiously.

Laboratory Test Alterations: BUN, AST, LDH, ALT, bilirubin, alkaline phosphatase, protein-bound iodine, uric acid (with colorimetric test). H&H;, WBCs. False + Coombs' test. Interference with tests for urinary glucose and ketones.

Overdose Management: Symptoms: Muscle twitching, blepharospasm. Also see Side Effects. Treatment: Immediate gastric lavage for acute overdose. Maintain airway and give IV fluids carefully. General supportive measures.

Drug Interactions: Antacids / Effect of levodopa R/T absorption from GI tract Anticholinergic drugs / Possible levodopa effect R/T levodopa breakdown in stomach (R/T delayed gastric emptying time) Antidepressants, tricyclic / Levodopa effect R/T GI tract absorption; also, risk of hypertension Benzodiazepines / Levodopa effect Clonidine / Levodopa effect Digoxin / Digoxin effect Furazolidone / Levodopa effect R/T liver breakdown Guanethidine / Hypotensive drug effect Hypoglycemic drugs / Levodopa upsets diabetic control with hypoglycemic agents Indian snakeroot / Effect of levodopa but extrapyramidal symptoms MAO inhibitors / Concomitant administration may result in hypertension, lightheadedness, and flushing R/T breakdown of dopamine and norepinephrine formed from levodopa Methionine / Levodopa effect Methyldopa / Additive effects including hypotension Metoclopramide / Bioavailability of levodopa; metoclopramide effect Papaverine / Levodopa effect Phenothiazines / Levodopa effect R/T uptake of dopamine into neurons Phenytoin / Antagonizes levodopa effect Propranolol / May antagonize the hypotensive and positive inotropic effect of levodopa Pyridoxine / Reverses levodopa-induced improvement in Parkinson's disease Thioxanthines / Levodopa effect in Parkinson clients Tricyclic antidepressants / Levodopa absorption effect

How Supplied: Capsule: 250 mg; Tablet: 100 mg, 250 mg, 500 mg

Dosage
•Capsules, Tablets Parkinsonism.
Adults, initial: 250 mg b.i.d.-q.i.d. taken with food; then, increase total daily dose by 100-750 mg/3-7 days until optimum dosage reached (should not exceed 8 g/day). Up to 6 months may be required to achieve a significant therapeutic effect.