Dopamine agonists

Dopamine agonists act like dopamine and directly stimulate dopamine receptors. They are used alone in early Parkinson's or with levodopa when the disease advances, to help it work more effectively.

There are three main products available: rotigotine, pramipexole and ropinirole. Pramipexole and ropinirole are available as immediate-release (taken three times daily) and modified-release tablets (taken once daily). Rotigotine is available in a daily transdermal patch formulation, which can be useful for patients encountering swallowing difficulties or those with a heavy tablet burden. Patients should be started at low doses, with slow up-titration.

Dopamine agonists have the same side effects as levodopa, but they are often more severe as the medicines are more potent. There are also more psychiatric side effects with dopamine agonists than with levodopa. These can cause sudden onset of sleep or excessive daytime sleepiness,which patients should be warned of, particularly if they drive or operate machinery.

Dopamine agonists can also cause confusion and hallucinations as well as impulsive and compulsive behaviour, such as pathological gambling, binge eating and hypersexuality. Patients and their carers should be advised about the risk of impulsive and compulsive behaviour when starting a dopamine agonist. Patients should not stop their medicines suddenly if these behaviours develop as side effects, but should instead be referred back urgently to their Parkinson's specialist as the medicine needs to be withdrawn slowly or the dose reduced until symptoms resolve.

Monoamine oxidase B inhibitors

Monoamine oxidase B (MAO-B) inhibitors are used alone (often in early Parkinson's) or as an adjunct to levodopa to decrease end-of-dose deterioration as the condition progresses. They work by inhibiting MAO-B, which decreases the breakdown of dopamine.

There are two MAO-B inhibitors available: rasagiline and selegiline, both of which are taken once daily. Selegiline can have an alerting effect, including insomnia, nightmares and vivid dreams, so it is best taken in the morning.

MAO-B inhibitors are not as potent as levodopa or dopamine agonists, but they have similar side effects. They also have many interactions with antidepressants and other medicines, including OTC remedies, so care needs to be taken when recommending OTC products.