levodopa and dopamine decarboxylase inhibitors
L-DOPA is a precursor of dopamine. Dopamine iteself does not cross the blood-brain barrier and so is no effective as a drug. L-DOPA does enter the brain and is converted to dopamine in the striatum.
L-DOPA is usually given in conjunction with an inhibitor of dopamine decarboxylase. The inhibitor does not cross the blood-brain barrier hence the side-effects of peripheral dopamine production, such as nausea, are reduced while the central actions of L-DOPA are augmented.
NICE state that it is not possible to identify a universal first-choice drug therapy for people with early Parkinson's disease (PD). A possible inititial first-choice therapy is levodopa therapy (2)
- the dose of levodopa should be kept as low as possible to maintain good function in order to reduce the development of motor complications
- modified-release levodopa preparations may be used to reduce motor complications in people with later PD, but should not be drugs of first choice
- Clarke CE (1999). Managing early Parkinson's disease. The Practitioner; 243: 39-47.
- NICE (June 2006). Parkinson's disease
Last reviewed 04/2018