Levodopa is an active substance from the group of antiparkinsonian drugs for the treatment of Parkinson’s disease. The aim of the therapy is to increase the concentration of dopamine in the basal cells of the cerebrum. Levodopa is a so-called prodrug and, in contrast to the activated active substance dopamine, can cross the blood–brain barrier, so that it is effective where an increased dopamine concentration is desired therapeutically.
Levodopa is always given in combination with a decarboxylase inhibitor (e.g. carbidopa, benserazide) to reduce peripheral side effects (e.g. nausea and vomiting). If a patient is treated with levodopa for a longer period of time, movement disorders may occur, which can then be treated therapeutically with drugs (dopamine antagonists).
Mode of action
Levodopa is used to compensate for the lack of dopamine in the brain, which is caused by the loss of function and death of dopaminergic nerve cells in the black matter of the brain in the presence of Parkinson’s disease. The symptoms of Parkinson’s disease, such as slowed movement and stiffness, are well treatable with the use of levodopa. The symptoms of tremor, speech disorders, difficulty swallowing and stiff walking, on the other hand, cannot be treated with levodopa, so that only partial improvement can be achieved with the drug. The effect of levodopa is based on the fact that dopamine interacts with the postsynaptic dopaminergic receptors D1 and D2.
Fields of application
Levodopa must not be used in the case of Parkinson’s disease caused by medication. However, levodopa is used for the treatment of “normal” Parkinson’s disease and the so-called “restless leg syndrome”.
Contraindications
Levodopa must not be used in cases of allergy (hypersensitivity), narrow-angle glaucoma (disturbance of the outflow of excess tear fluid and thus an increase in pressure in the eye), melanoma, simultaneous use of non-selective MAO inhibitors or the use of metoclopramide.
Interactions
If a high-protein meal, antacids, dopamine antagonists (neuroleptics) or iron is taken at the same time as the drug levodopa, it is highly likely that levodopa will become less effective. If levodopa is combined with MAO-A inhibitors, a crisis-like rise in blood pressure may occur. For this reason, MAO-A inhibitors should be discontinued 2 weeks before starting therapy with levodopa.
If levodopa is taken together with antihypertensive drugs, orthostatic hypotension (circulatory disorder) may occur. Interactions with levodopa have also been observed when taking phenytoin and papaverine. Here, levodopa has been shown to be less effective in the treatment of Parkinson’s disease.