Levodopa

From DrugPedia: A Wikipedia for Drug discovery

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Revision as of 09:09, 24 October 2008

Pronouncation: (LEE-voe-DOE-puh)

Class: Antiparkinson agent

Trade Names:

Dopar

- Capsules 100 mg

- Capsules 250 mg

- Capsules 500 mg

Contents 1 Pharmacology 2 Indications and Usage 3 Contraindications 4 Dosage and Administration 5 Storage/Stability 6 Drug Interactions 7 Adverse Reactions 8 Precautions 9 Overdosage 10 Patient Information

Pharmacology

Absorption

Absorbed from the small bowel. T max is 0.5 to 2 h and may be delayed in presence of food. Rate of absorption is dependent upon rate of gastric emptying, pH of gastric juice, and length of time drug is exposed.

Distribution

Does not cross the blood-brain barrier.

Metabolism

Metabolites are dopamine and homovanillic acid (HVA). Extensively metabolized (greater than 95%) in the periphery and by the liver.

Elimination

Plasma t ½ is 1 to 3 h. Excreted primarily in the urine; 13% to 42% of HVA excreted in the urine within 24 h.

Indications and Usage

Treatment of idiopathic, postencephalitic, and symptomatic parkinsonism.

Unlabeled Uses

Relief of herpes zoster (shingles) pain and restless leg syndrome.

Contraindications

Narrow-angle glaucoma; concomitant MAOI therapy (excluding MAOI-type B agents such as selegiline); history of or suspected melanoma.

Dosage and Administration

Adults

PO 0.5 to 1 g/day in 2 to 4 divided doses initially. Increase dosage gradually in increments up to 0.75ߙg/day every 3 to 7 days as tolerated (max, 8 g/day).

General Advice

• Give medication with food to reduce nausea.

• Tablets can be crushed and capsules opened for mixing with small amount of fruit juice for patients being given tube feedings.

Storage/Stability

Store at room temperature in light-resistant container.

Drug Interactions

Anticholinergics, benzodiazepines, hydantoins, methionine, papaverine, pyridoxine, tricyclic antidepressants

May reduce the effectiveness of levodopa.

MAOIs (except selegiline)

Causes hypertensive reactions.

Laboratory Test Interactions

Antiglobulin Coombs' test

With extended therapy, drug may cause false-positive results.

Uric acid study

May result in elevated values with colorimetric method but not with uricase method.

Adverse Reactions

Cardiovascular

Cardiac irregularity or palpitation; orthostatic hypotension; hypertension; phlebitis.

CNS

Ataxia; headache; dizziness; numbness; weakness; faintness; confusion; insomnia; nightmares; mental changes (eg, psychosis, paranoia, depression, dementia, hallucinations, delusions); agitation; anxiety; fatigue; euphoria; psychopathology; adventitious movements (eg, choreiform or dystonic movements); increased hand tremor; muscle twitching; trismus; bradykinesia (“on-off” phenomenon).

Dermatologic

Flushing; skin rash; sweating.

EENT

Blepharospasm; diplopia; blurred vision; dilated pupils; impaired taste perception; oculogyric crisis.

GI

Anorexia; nausea; vomiting; abdominal pain; distress; dry mouth; dysphagia; excessive salivation; bruxism; GI bleeding; duodenal ulcer.

Genitourinary

Urine retention; urinary incontinence; priapism.

Hematologic

Hemolytic anemia; anemia; agranulocytosis; leukopenia.

Hepatic

Elevated AST, ALT, LDH.

Respiratory

Bizarre breathing patterns.

Miscellaneous

Malaise; hot flashes; weight gain or loss; dark sweat or urine; latent Horner's syndrome; elevated BUN, bilirubin, alkaline phosphatase, and protein-bound iodine; activation of malignant melanoma.

Precautions

Pregnancy

Pregnancy category undetermined.

Lactation

Undetermined. Do not use in breast-feeding mothers.

Children

Safety and efficacy in children younger than 12 yr of age not established.

Concomitant conditions

Use with caution in patients with severe CV or pulmonary disease; renal, hepatic or endocrine disease; affective disorder; major psychosis; and cardiac arrhythmias.

Dosage reduction

Decrease levodopa dose 75% to 80% when used in combination with carbidopa.

MI

Administer cautiously to patients with history of MI who have residual arrhythmias. Administer drug in facility with coronary or intensive care unit.

Psychiatric patients

Use cautiously. Observe all patients for development of depression or suicidal ideation.

Upper GI hemorrhage

May occur in patients with prior history of peptic ulcer.

Overdosage

Symptoms

Shock, coma, blepharospasm, arrhythmias, seizures, CNS depression, muscle twitching.

Patient Information

• Advise patient to take medication with food.

• Teach patient to avoid sudden position changes to avoid orthostatic hypotension.

• Inform patient that fluctuation in effectiveness of levodopa sometimes occurs with long-term therapy. Instruct patient to notify health care provider if fluctuation in effectiveness is experienced.

• Advise patient to avoid use of OTC vitamins, fortified cereals and vitamin B 6 , which reverse effects of levodopa.

• Warn patient not to increase dosage in an attempt to reduce parkinsonian symptoms more quickly. Noticeable lessening of symptoms may take more than 6 mo to occur.

• Advise patient to report the following symptoms to health care provider: uncontrolled movements, mood or mental changes, irregular heartbeats, difficulty in urination, severe or persistent nausea or vomiting, worsening of parkinsonian symptoms.

• Advise patient that levodopa may cause urine and perspiration to become dark, which is a harmless adverse reaction.

• Inform patient that drug may cause drowsiness and to use caution while driving or performing tasks that require mental alertness.

• Instruct patient to take sips of water frequently, suck on ice chips or sugarless hard candy, or chew sugarless gum if dry mouth occurs.