Dopaminergic medicines

Dopaminergic medications replace depleted dopamine. Dopaminergic medication can be used to treat tremor, stiffness, slowness, and walking problems. They can sometimes have a beneficial impact on sleep, mood and cognition. Dopaminergic medications make up the majority of medicines used to treat PD and they can sometimes be used in combination due to their different mechanisms of action in the body. Dopamine medications are listed below followed by a list of common side effects for this group.

Levodopa

Levodopa is one of the oldest medications used for PD and is still the most effective, even at low doses. Levodopa is absorbed in the intestine and transported to the brain. Dopamine nerve cells absorb the levodopa and convert it to dopamine. Essentially, taking levodopa tablets attempts to restore adequate levels of dopamine in the brain. Levodopa is combined with carbidopa (combination is called Sinemet) to reduce nausea side effects. High protein meals eaten within an hour of taking levodopa can interfere with absorption. See accompanying article on protein, nutrition and levodopa absorption. The following chart outlines the different forms of carbidopa/levodopa (Note: carbidopa/levodopa/entacapone or Stalevo is listed separately under COMT inhibitors).

As you review the chart below, you will notice the different types and strengths of carbidopa/levodopa. Make sure you know which formulation you are taking to prevent medication errors:

Carbidopa/Levodopa:

Amantadine (Symmetrel)  

Amantadine is a medication originally used to treat the common flu but later found to improve the symptoms of PD. In some people, Amantadine helps reduce dyskinesia. Common dose is 100mg one to three times a day. Amantadine can cause a lacy brown rash most often seen in the legs with long-term use. Other side effects can include dry eyes, dry mouth, constipation and tissue swelling, especially the legs. Amantadine is used with caution in people experiencing thinking problems or hallucinations. Amantadine is metabolized through the kidneys and people with kidney disease may require lower doses.

Dopamine Agonists

Dopamine agonists are a group of medications that mimic the effects of dopamine. These medications have a longer lasting effect and can help control symptoms over a longer period of the day. The following chart lists dopamine agonists used in the USA. Apomorphine (Apokyn) is injected under the skin to provide very fast action typically within 20 minutes and is used for rescue treatment when wearing off is abrupt or unpredictable. The rotigotine patch is currently on hold by the FDA due to problems with the patch delivery system.

Dopamine Agonists:

COMT Inhibitors

Catechol-o-methyl-transferase (COMT) inhibitors help slow the breakdown of dopamine in the body. This group of medicines is used when levodopa therapy is associated with off periods as they increase the time of effectiveness for a levodopa dose. COMT inhibitors increase on time and reduce off time, especially end of dose wearing off. Entacapone must be given at the same time as your carbidopa/levodopa dose and can cause dark colored urine and permanent stains on clothes. A combination pill called Stalevo combines carbidopa/levodopa and entacapone into one convenient pill. Tolcapone (Tasmar) is used less frequently due to potential liver toxicity requiring blood testing of liver function. Both of these medications can cause diarrhea.

COMT Inhibitors:

MAOB Inhibitors

Monoamine Oxidase Type B (MAOB) inhibitors also slows the breakdown of dopamine in the body and brain. These inhibitors are used as early treatment when symptoms are mild and can be added when problems with wearing off occur and symptoms return between medication doses.

MAO B Inhibitors:

Learn about side effects of dopaminergic medicines in the accompanying article.