Antiparkinsonian Drugs Question And Answers

Antiparkinsonian Drugs

 

Question 1. Give A Brief Account Of Levodopa.

Levodopa is a dopamine precursor.

Account On Levodopa Mechanism of Action

• Levodopa crosses the blood-brain barrier and is taken up by presynaptic terminals of dopaminergic neurons and is dehydroxylated to dopamine.
• Levodopa is converted to dopamine in peripheral tissue and dopamine thus formed acts on the heart, blood vessels, and peripheral organs.

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Account Of Levodopa Pharmacological Actions

• CNS: Hypokinesia, rigidity, and tremors improve first, later other symptoms like gait, speech, sialorrhea, and mood are normalized.
• CVS: It causes tachycardia
• CTZ: It causes nausea and vomiting.
• Endocrine: It inhibits prolactin release.

Account Of Levodopa Adverse Reaction

• GIT: It causes nausea, vomiting, and anorexia in early treatment. Tolerance to emetic effect develops slowly.
• CVS: It causes postural hypotension, palpitation, cardiac arrhythmia, and angina.
• Abnormal movement: Dyskinesia, tics, tremors, and choreoathetosis movements may occur.
• Behavioral effect: Agitation, anxiety, nightmares, depression, confusion, and mania.

Question 2. Explain Why Levodopa Is Given Along With Carbidopa?
Or
Write A Short Note On Levodopa And Carbidopa Combination.
Answer:

Decarboxylase inhibitor, i.e. carbidopa prevents the conversion of levodopa to dopamine outside the brain by inhibiting dopa decarboxylase enzyme peripherally. Thus, a greater concentration of levodopa can cross the blood-brain barrier and reaches its site of action in the brain.

Benefits obtained from combining levodopa with carbs-dopa are:

• The combination ensures less degree of peripheral decarboxylation of levodopa and thus more entry into the brain. This improves the efficacy of levodopa
• The greater amount of levodopa also contributes to the possibility of a reduction in the dose of the drug administered.
• Reduced conversion of levodopa and less formation of dopamine in the periphery leads to a reduction in the incidence of adverse effects like nausea, vomiting, cardiac complications, etc. with levodopa.
• Reduced cost of total therapy to the patient because of lesser amount of drugs required to maintain their clinical efficacy.
• Sustained levels of dopamine attained in the CNS ensure minimal incidence of ”on-off phenomenon.
• Reduction in drug interactions especially with drugs acting on the dopa decarboxylase enzyme like pyridoxine.