Levodopa
The cornerstone of Parkinson’s medication is levodopa. Levodopa, or L-dopa, is a so-called amino acid that exists naturally in the body and also in tiny amounts in some vegetables. The name is an abbreviation of dihydroxy-L-phenylalanine. Levodopa medications are: Madopar, Madopar depot, Madopar Quick, Madopar Quick Mite, Sinemet, Sinemet depot and Stalevo, and, during later stages of the disease, the pump-based medication levodopa/carbidopa. Levodopa is very effective against Parkinson’s symptoms. It is the precursor of dopamine, but levodopa is used instead because dopamine cannot pass directly into the brain. Medication is started with low doses that are increased gradually until the best possible symptom relief is obtained for the individual. Levodopa begins to have an effect after a few weeks’ use, but sometimes it can take up to several months to achieve the maximum benefit.
The uptake and transportation of levodopa into the blood can be obstructed by the amino acids of proteins in food. In order to achieve the best possible result, levodopa should therefore be taken approximately 30 minutes before eating food containing proteins, e.g. meat, fish, cheese, milk, egg etc. Levodopa is absorbed in the upper small intestine and therefore is also dependent on gastric emptying.
Dopamine agonists
These substances cross into the brain and mimic the effects of dopamine in the dopamine receptors. Cabaser (cabergoline), Parlodel (bromocriptine), Requip (ropinirole), Mirapexin (pramipexole) and apomorphine (pen and pump administration) are dopamine agonists. In addition, one dopamine agonist, Neupro (rotigotine), is now available in patch form to apply to the skin. Dopamine agonists can be used alone or in combination with levodopa. They often provide good relief of symptoms, especially tremor. Dopamine agonists also seem to have some antidepressive effect.
Dopamine enhancers
Levodopa has a relatively short duration of action. Therefore, additional medication can be used that smooth out and prolong its effect. Both inside and outside the brain, enzymes break down dopamine to substances that are of no use in Parkinson’s treatment.
One such enzyme is catechol-O methyl transferase (COMT). If this enzyme is blocked, the levodopa dose will last longer and the fluctuations of the brain’s dopamine levels during the day will be reduced. At present, two COMT inhibitors are available: Comtess (entacapone) and on-licence Tasmar (tolcapone). These medications have symptom-relieving effects only in combination with levodopa, not by themselves. Both should therefore be taken in combination with levodopa medication.
Another enzyme, monoamine oxidase type B (MAO-B) breaks down dopamine in the brain. Inhibitors of this enzyme, e.g. Eldepryl (selegiline) and Selegiline (selegiline), increase the dopamine level and provide symptom relief, but not as effectively as levodopa or dopamine agonists. Eldepryl also has a certain antidepressive effect. Some research data indicates that the progression of Parkinson’s could be slowed by Eldepryl, which is usually taken once every morning together with food. The most recent dopamine booster is Azilect (rasagiline).
Symmetrel (amantadine) can be used as initial treatment, primarily in older people or to improve the effect of levodopa. Amantadine is actually a medication used against viral disease, but it can be effective in Parkinson’s by increasing the release of dopamine from cells that still produce it.
