Dopamine agonists: impulse control disorders and sudden sleep onset
Dopamine agonists directly stimulate dopamine receptors, and a distinctive side effect is impulse control disorders: compulsive behaviours such as gambling and compulsive shopping.
Remember
Before a dopamine agonist is started, patients and their families need to hear about the risk of impulse control disorders and sudden sleep attacks; the behaviours usually reverse when the drug is reduced or stopped.
Memory aid
agonists press the reward button directly, even in a brain that is losing dopamine elsewhere
Picture an agonist pressing the reward button itself, which helps to explain why compulsive behaviours can follow.
Parkinson's disease is a condition in which the nigrostriatal neurones (the dopamine neurones that run from the substantia nigra to the striatum) degenerate. Dopamine agonists stimulate dopamine receptors directly, bypassing the need for dopamine to be made and released by the degenerating neurones. Ropinirole, pramipexole and rotigotine (a patch) are the non-ergot agonists now used as standard, unlike the older ergot-derived agonists such as bromocriptine and cabergoline.
This direct stimulation is not confined to the movement circuits. It also reaches the reward pathways, and over-stimulating them is thought to underlie impulse control disorders. These include gambling, compulsive shopping, binge eating and punding, which means repetitive, purposeless activity such as sorting objects.
They are reported in around 15% of patients taking dopamine agonists, so patients and their families should be warned explicitly before treatment starts. The behaviours usually reverse when the drug is reduced or stopped.
Sudden onset of sleep, called sleep attacks, is another class effect of dopamine agonists (a side effect shared across the drug group), and it impacts driving safety. A patient who has had sudden onset of sleep should be advised not to drive.
Levodopa is a precursor that must be converted to dopamine in the brain. Impulse control disorders can occur with levodopa too, but they are more likely with dopamine agonists.
Key facts
- Direct action
- ropinirole, pramipexole and rotigotine act on dopamine receptors themselves, whereas levodopa is a precursor that must be converted to dopamine in the brain.
- Receptor type
- ropinirole stimulates D2-type receptors, which are one family of dopamine receptors.
- Reported rates
- impulse control disorders are reported in around 15% of patients taking dopamine agonists.
- Examples
- compulsive gambling, compulsive shopping, binge eating and punding (repetitive, purposeless activity), among others.
- Course
- the behaviours are usually reversible when the drug is reduced or stopped.
- Sleep and driving
- sudden onset of sleep impacts driving safety, so patients who have had sleep attacks should be advised not to drive.
Exam traps
- In Parkinson's disease, fibrosis of the lungs or heart valves is not the usual problem of the dopamine agonists used today, because it is linked to the older ergot-derived agonists, which are now largely abandoned.
- Severe neutropenia, meaning a dangerously low neutrophil count, is not recognised as a class effect of dopamine agonists; behavioural, sedative and cardiovascular effects are among the typical ones.
- A new behaviour such as compulsive gambling after starting a dopamine agonist is not explained by degeneration of the nigrostriatal dopamine neurones, since that loss underlies Parkinson's disease itself and is a gradual process.
Read the full notes
Tested in 11 SimpleMed+ questions
Practice it in Pharmacology, with the answer and a full explanation after every question.
Practice these questions