11 Questions
What is the primary route of administration of Levo-dopa?
Orally
What is the role of Carbidopa in Levo-dopa therapy?
To prevent the conversion of Levo-dopa to dopamine in the systemic circulation and liver
What percentage of administered Levo-dopa reaches the brain unaltered?
1-3%
What is the primary mechanism of Levo-dopa absorption in the small intestine?
L-amino acid transporter
What is the recommended dosing frequency of Levo-dopa and Carbidopa combination?
Three or four times daily
Why are controlled- or sustained release formulations not recommended initially?
They do not allow proper assessment of the patient's response
What is a common adverse effect of L-dopa when given alone?
Nausea, anorexia, and vomiting
What is a motor complication that develops in at least 50% of patients after 5-10 years of L-dopa treatment?
Dyskinesia
What is a behavioral effect of L-dopa that can be treated with atypical antipsychotic agents?
Hallucinations
What is a rare but potentially fatal complication seen in Parkinson's disease patients?
Parkinsonism-hyperpyrexia syndrome
Why should L-dopa and other antiparkinson medications not be stopped abruptly?
To prevent Parkinsonism-hyperpyrexia syndrome
Study Notes
Levo-dopa Pharmacology
- Administered orally, absorption from small intestine delayed by food, enters brain via L-amino acid transporter and converted to dopamine by decarboxylation reaction
- Metabolites excreted by kidney, half-life 1-3 hours, only 1-3% of administered L-dopa reaches brain unaltered
Levo-dopa and Carbidopa
- Carbidopa inhibits peripheral decarboxylation, increases L-dopa half-life, and allows more L-dopa to cross blood-brain barrier
- Combination available in immediate-release tablets (Sinemet) with various strengths (10/100, 25/100, 25/250 mg)
- Dosing 3-4 times daily, controlled-release formulations available but not recommended initially
Adverse Effects
Gastrointestinal
- Nausea, anorexia, vomiting in 80% of patients with L-dopa alone, reduced to <20% with combination therapy
- Mitigated by starting with small doses, taking with meals, adding carbidopa, or domperidone
Cardiovascular
- Arrhythmias, tachycardia, extra systoles possible, reduced by combination therapy
- Hypertension with large doses, postural hypotension common initially
Behavioral
- Depression, anxiety, agitation, insomnia, sleep attacks, confusion, and hallucinations reported
- Treated with atypical antipsychotic agents, more common with combination therapy
Motor Complications
- Dyskinesia (involuntary movements) in 60% of patients after 10 years, likely due to relative excess of L-dopa
- Motor fluctuations (wearing-off reaction or on-off phenomenon) due to disease progression and reduced ability to store and release dopamine
Other Adverse Effects
- Impulse control disorders more pronounced with dopamine agonists, range from non-bothersome to destructive behaviors
- Parkinsonism-hyperpyrexia syndrome (rare, fatal complication) can occur when antiparkinson medications are suddenly reduced or ceased
This quiz covers the pharmacology of Levo-Dopa, a medication used to treat Parkinson's disease. It explores the administration, absorption, and metabolism of Levo-Dopa, as well as its efficacy and potential complications.
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