Carbidopa Uses, Side Effects, and More

 Carbidopa

Brand name:- lodosyn. 

Carbidopa is always given with levodopa. It works by preventing levodopa from being broken down before it reaches the brain. This allows for a lower dose of levodopa, which causes less nausea and vomiting.

Pharmacodynamic:- 

When mixed with levodopa, carbidopa inhibits the peripheral conversion of levodopa to dopamine and the decarboxylation of oxitriptan to serotonin by aromatic L-amino acid decarboxylase. This results in an increased amount of levodopa and oxitriptan available for transport to the central nervous system. Carbidopa also inhibits the metabolism of levodopa in the GI tract, thus, increasing the bioavailability of levodopa.

The presence of additional units of circulating levodopa can increase the effectiveness of the still functional dopaminergic neurons and it has been shown to alleviate symptoms for a time. The action of carbidopa is very important as levodopa is able to cross the blood-brain barrier while dopamine cannot. Hence the administration of carbidopa is essential to prevent the transformation of external levodopa to dopamine before reaching the main action site in the brain.

The coadministration of carbidopa with levodopa has been shown to increase the half-life of levodopa more than 1.5 times while increasing the plasma level and decreasing clearance. The combination therapy has also shown an increase of the recovery of levodopa in urine instead of dopamine which proves a reduced metabolism. This effect has been highly observed by a significant reduction in levodopa requirements and a significant reduction in the presence of side effects such as nausea. It has been observed that the effect of carbidopa is not dose-dependent.

Mechanism of action:- 

Carbidopa is an inhibitor of the DDC which in order, inhibits the peripheral metabolism of levodopa. DDC is very important in the biosynthesis of L-tryptophan to serotonin and the modification of L-DOPA to dopamine.

DDC can be found in the body periphery and in the blood-brain barrier.4 The action of carbidopa is focused on peripheral DDC as this drug cannot cross the blood-brain barrier.8 Hence, it will prevent the metabolism of levodopa in the periphery but it will not have any activity on the generation of dopamine in the brain.

Used:- 

Used with a combination levodopa/carbidopa product to treat symptoms of Parkinson's disease or Parkinson-like symptoms (such as shakiness, stiffness, difficulty moving).

Sides effects:- 

Dizziness, lightheadedness, nausea, vomiting, loss of appetite, trouble sleeping, unusual dreams, or headache may occur.

Doses:-  As directed by your doctor.