Carbidopa is given in combination L-dopa in Parkinsonian

Carbidopa/levodopa remains the most effective drug to treat PD. In addition to helping prevent nausea, carbidopa prevents levodopa from being converted into dopamine prematurely in the bloodstream, allowing more of it to get to the brain.

1. Why carbidopa is given in combination levodopa in Parkinsonian therapy? Prof. Amol B. Deore (Lecturer) Department of Physiology and Pharmacology MVP’s Institute of Pharmaceutical Sciences, Nashik

2. What is parkinsonian syndrome

3. Parkinsonian is a chronic progressive motor disorder of the CNS characterized by extrapyramidal symptoms including dyskinesia, muscular rigidity, tremors, dementia and mental depression.

4. In Parkinson's disease, certain neurons in the brain gradually break down or die. Many of the symptoms are due to a loss of neurons that produce a neurotransmitter in your brain called dopamine . When dopamine levels decrease, it causes abnormal brain activity, leading to signs of Parkinson's disease.

5. Progressive degeneration of dopaminergic neurons in the substantia nigra leads to deficiency of dopamine in corpus striatum. As a result there is increased cholinergic transmission (by Ach) in the basal ganglia.

6. dopamine concentration becomes very low and Acetylcholine extremely rise (imbalance) in the corpus striatum is responsible for Parkinsonian .

7. Levodopa Precursor of Dopamine synthesis Levodopa DOPAMINE dopa decarboxylase

8. Levodopa: precursor of dopamine synthesis Carbidopa : inhibits peripheral dopa decarboxylase ( in plasma )

9. Levodopa is the metabolic precursor of dopamine biosynthesis. Levodopa crosses the blood-brain barrier (BBB) and converted into dopamine in the CNS. Levodopa dopa decarboxylase Dopamine The enzyme dopa decarboxylase converts the l-Dopa into Dopamine. Hence concentration of dopamine elevated in the brain to recover the patient from Parkinsonian symptoms.

10. dopa decarboxylase (Peripheral) dopa decarboxylase BRAIN BLOOD BBB Levodopa Dopamine Levodopa Dopamine Low bioavailability Therefore bioavailability of l-Dopa becomes very low.

11. dopa decarboxylase (Peripheral) dopa decarboxylase BRAIN BLOOD BBB CARBIDOPA Levodopa DOPAMINE High bioavailability LEVODOPA

12. This allows a greater fraction of l-Dopa drug molecules to cross the BBB and producing higher levels of dopamine in the motor regulating areas of brain and improves the symptoms of parkinsonian , akinisia and bradykinesia .

13. Carbidopa does not cross BBN and hence dose not interferes with conversion of l-Dopa into dopamine in the CNS. Thus bioavailability of l-Dopa increases up to the 75%. Carbidopa + Levodopa [1:10] Tablet- 10mg Carbidopa + 100mg Levodopa Tablet– 25mg Carbidopa + 250mg Levodopa

14. The dose of levodopa can be reduced by as much as 75%. Adverse effects of levodopa like nausea, vomiting, and cardiovascular adverse reaction can be prevented. The control of symptoms is smoother. The number of daily doses can be reduced without loss of control. Degree of improvement is higher than levodopa alone. Advantages of combination of carbidopa with levodopa

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