Treatment options
Once in the body, molecules called enzymes break down levodopa. Unfortunately, this “breakdown” limits the amount of medication that can reach the brain where it is needed. There are two main enzymes that cause the breakdown of levodopa. They are called peripheral dopa-decarboxylase (DDC) and catechol-O-methyltransferase (COMT).

Blocking these two enzymes can reduce levodopa’s breakdown. This helps the medication get where it needs to go in the brain.

Soon after levodopa was introduced, a medication known as a peripheral dopa-decarboxylase (DDC) inhibitor was developed. DDC inhibitors block one of the enzymes that causes levodopa to breakdown to dopamine. They make sure that more of the medication reaches where it needs to go in the brain, which can also cut down some potential side effects, such as nausea and vomiting. These side effects can occur when dopamine is at high levels in the blood stream. There is one DDC inhibitor available in the U.S., called carbidopa.

In the 1990s, another class of medication was developed known as COMT inhibitors. COMT inhibitors, such as entacapone and tolcapone, provide longer and smoother availability of levodopa to the brain. Combining a COMT inhibitor with levodopa/carbidopa can improve and lengthen the amount of time symptoms are under control.

If you start to notice that your levodopa medication is not working as well as it used to, share these observations with your doctor or other healthcare professional. He or she may be able to adjust your medication to provide better control of your symptoms.

In 2003, a new medication combining levodopa with both a DDC inhibitor and a COMT inhibitor all in one tablet became available.