Dopamine agonists (DAs) do not replace endogenous dopamine, but mimic the action of dopamine at the postsynaptic dopaminergic receptor.
There are a number of different DAs currently available; the difference between them lies in the amount of activity that they have for a specific dopamine receptor subtype and whether they are ergot- or non-ergot-derived (Table 6).
Dopamine agonists are an effective treatment for the motor features of early PD, and are used in combination with other therapies to control motor symptoms in patients with late PD.
Dopamine agonists can be beneficial either as monotherapy or as an adjunct to levodopa. However, virtually all PD patients will require levodopa at some point during their disease because of the superior symptom control provided by this agent. (Figure 13)
The lower antiparkinsonian efficacy of DAs in comparison with levodopa means that when selecting treatment, the benefit of DAs, in terms of side effects, must be balanced against the level of symptomatic control required by an individual patient.[51-53]
The approach of giving DAs as first-line treatment is not always favoured; especially when physicians feel it is important not to compromise immediate improvements in mobility and QoL because of the risk of future complications.
Furthermore, some patients respond poorly to, or cannot tolerate, DAs: