Medications that can replace dopamine, the depleted neurotransmitter in the brain, are the mainstay of treatment. Levodopa, a precursor of dopamine, can be converted to dopamine in the brain. It is administered in combination with carbidopa (as in Sinemet and Kinson) or benserazide (as in Madopar), to maximise the delivery of levodopa to the brain and minimise side effects. These medications are usually effective for many years. However, the response tends to wear off or becomes less predictable with time.

Medications such as bromocriptine (Bromocriptine-BC, Bromohexal, Bromolactin, Kripton, Parlodel), pergolide (Permax), cabergoline (Cabaser) and apomorphine (Apomine) stimulate the dopamine receptors in the brain and therefore mimic the action of dopamine. They can be useful at all stages of Parkinson’s disease. In younger onset Parkinson’s disease agonists are sometimes used as initial treatment but in others agonists are prescribed as levodopa sparing agents or introduced once the response to levodopa starts to diminish.

This group of medications was the first available treatment for Parkinson’s disease before levodopa. They block the effect of acetylcholine, another brain chemical, to re-balance its levels with dopamine. They include benztropine (Cogentin, Benztrop), biperidine (Akineton) and benzhexol (Artane). Some antihistamines such as diphenhydramine (Unisom Sleepgels) also have anticholinergic activity and a useful sedative effect. All these drugs are now rarely used because of the relatively modest benefits that they give compared with their side effect profile.

This drug has both anticholinergic and dopamine agonist properties. It can be useful for many patients in controlling drug-induced involuntary movements (diskinesia).

Medications such as selegiline (Elderpryl, Selgene) prevent the breakdown of available dopamine within the brain and therefore prolong the action of levodopa.

Newer medications such as entacapone (Comtan) and, in some cases, tolcapone (Tasmar), are also used along with levodopa. By blocking an enzyme known as COMT that breaks down levodopa in the intestine and brain, they prolong the action of levodopa and reduce motor fluctuations.