Which substance prevents Levodopa from being metabolized in the gut and allows it to reach the brain?

Carbidopa is the substance that prevents the metabolism of Levodopa in the gut, thereby enhancing its availability to reach the brain. Levodopa is a precursor to dopamine and is commonly used in the treatment of Parkinson's disease. When administered alone, a significant portion of Levodopa is converted into dopamine in the peripheral tissues before it can cross the blood-brain barrier, which reduces its effectiveness.

Carbidopa acts as an inhibitor of the enzyme aromatic L-amino acid decarboxylase. By inhibiting this enzyme, carbidopa prevents the conversion of Levodopa to dopamine in the gastrointestinal tract and peripheral tissues. This not only ensures that more Levodopa is available to penetrate the blood-brain barrier but also minimizes side effects associated with increased peripheral dopamine levels, such as nausea and vomiting. Thus, the combination of Carbidopa and Levodopa enhances the therapeutic effect of the treatment for individuals with Parkinson's disease.