The drug levodopa, also known as L-dopa, has been used since the 1960s as the primary drug treatment for Parkinson’s Disease.
Levodopa is a natural substance that is found in both plants and animals. The compound is actually a precursor to dopamine, and unlike dopamine, it is able to cross the blood-brain barrier. As a result, when given to people with Parkinson’s, levodopa is converted into dopamine by nerve cells in the brain.
When administered on its own, blood enzymes, known as AADCs, break down much of the levodopa prior it reaching the brain. As a result, only a small amount of levodopa crosses the blood-brain barrier and reaches the brain. However, combining levodopa with an decarboxylase enzyme inhibitor, such as carbidopa (Sinemet, or benserazide), allows more levodopa to reach the brain and helps reduce some of the side-effects of this therapy. Sinemet CR is a prolonged-release version of this drug.
Levodopa is absorbed into the blood stream in the gut and then transported to the brain, where it is transformed into dopamine. There, it is then released by brain cells and triggers dopamine receptors which lets the movement control areas of the brain to return to normal funstional levels.
The resulting increase in dopamine levels can reverse many of the disabling symptoms of Parkinson’s disease, but as time passes, side-effects may increase and dosage adjustments will be required to compensate. Levodopa is available in two main forms: a standard (or immediate) release form and a long-acting (controlled-release) form. The controlled release form provides a prolonged effect by slowing down the rate of levodopa absorption in the gut.
During early treatment, the side-effects from levodopa therapy are usually more than offset by the benefits of the treatment. However, as the disease progresses, levodopa works less evenly and less predictably, and the side-effects caused by the treatment become more pronounced.
Some of the side-effects of levodopa treatment include:
Confusion, Discoloration of urine/sweat Dizziness Drop in blood pressure (especially when standing) (a condition called orthostatic hypotension) Dry mouth Hallucinations Involuntary / abnormal movements (a condition known as dyskinesia), Nausea Sweating Vomiting Waxing and waning of the response to the drug (wearing off effects) is common.
With long term use, levodopa can also cause: Involuntary / abnormal movements (a condition known as dyskinesia), Neuropsychiatric problems, including confusion, hallucinations, and psychosis.
In spite of these side-effects, levodopa often allows people with Parkinson’s to extend the amount of time that they are able to lead relatively normal lives and, in many cases, it is effective for a number of years. In addition to these side-effects, levodopa can become less effective as the disease progresses and the symptoms become more severe, and the beneficial responses to levodopa can also become more erratic over time.
Response fluctuations may occur after 2-3 years of use. For these reasons newer drugs are often used, either alone or with levodopa.
If you experience these or any other side-effects, discuss them with your doctor. It may be necessary to change the dosage of your medication or change to another medication which may be more suitable for you.