Dopamine agonists: their role in the treatment of Parkinson's disease
- Neurology Department, Imperial College School of Medicine, Hammersmith Hospital, London W12 0NN, UK
Parkinson's disease is a chronic and disabling illness. There is still some uncertainty in its diagnosis, particularly in the early stages, as some other neurological conditions present with similar clinical features. There has been wide variation in the management of Parkinson's disease due to a lack of consensus on the best approach. Recently, United Kingdom specific guidelines for the management of Parkinson's disease have been produced1 which provide, where possible, evidence based recommendations and the collective opinion of a Parkinson's Disease Consensus Working Group, whose members have substantial experience in managing patients with the disease.
Current drug therapy in Parkinson's disease is symptomatic and primarily aimed at restoring dopaminergic function in the striatum. Levodopa, in combination with a peripheral decarboxylase inhibitor, is still the most effective symptomatic treatment.2 Levodopa enters dopaminergic neurons where it is metabolised to dopamine, replacing the depleted endogenous neurotransmitter. Along with its proved efficacy, levodopa is well tolerated, easy to administer, and relatively inexpensive.3 However, long term use is associated with disabling complications such as fluctuating motor responses and dyskinesias4-6 and narrowing of the therapeutic window.7 In addition, levodopa is toxic in vitro to dopaminergic neurons8 and in vivo its use could lead to formation of cytotoxic free radicals when exogenous dopamine is decarboxylated; these would cause damage to surviving dopaminergic neurons and potentially exacerbate the disease.9 10
In the light of these complications, the United Kingdom guidelines suggest that pharmacological intervention should be delayed until a diagnosis of Parkinson's disease has been confirmed by a specialist in movement disorders and the symptoms start to interfere with daily life.1 In addition, the United Kingdom guidelines recommend that treatment with levodopa should be delayed for as long as possible providing alternative drugs, such as dopamine agonists, can achieve adequate …