💊 Anticholinergics for Parkinson's

Anticholinergics are a class of drugs that block the action of acetylcholine. In Parkinson's disease, they are used to help rebalance neurotransmitter activity in the basal ganglia.

In Parkinson's disease, there is a relative excess of cholinergic activity compared to dopaminergic activity in the basal ganglia. Anticholinergics block muscarinic acetylcholine receptors, primarily M1 receptors, in the striatum. This reduces the cholinergic overactivity, thereby helping to alleviate some Parkinsonian symptoms, particularly tremor and rigidity.

Anticholinergics are primarily indicated for the treatment of drug-induced parkinsonism, often caused by antipsychotics, where they can help reduce extrapyramidal side effects. In idiopathic Parkinson's disease, they are mainly used for the management of troublesome tremor and rigidity, particularly in younger patients. Their use has largely been superseded by other agents due to their side effect profile.

Absolute contraindications include closed-angle glaucoma due to the risk of precipitating an acute attack. They are also contraindicated in prostatic hypertrophy with urinary retention and paralytic ileus. Caution is required in the elderly due to increased susceptibility to central nervous system side effects and in patients with cardiac arrhythmias.

Common anticholinergic side effects include dry mouth, blurred vision, constipation, and urinary retention. Central nervous system effects such as confusion, hallucinations, and memory impairment are particularly problematic, especially in older patients. Tachycardia and exacerbation of glaucoma can also occur.

Patients should be monitored for the development of anticholinergic side effects, particularly in the elderly. Regular assessment of cognitive function and urinary symptoms is important. Intraocular pressure should be checked in patients at risk of glaucoma.

Before prescribing, always check for a history of glaucoma, prostatic hypertrophy, or cognitive impairment. Counsel patients about the common side effects like dry mouth and constipation, and advise them to report any visual changes or urinary difficulties. Emphasise the importance of not stopping the medication abruptly.

Anticholinergics (e.g., procyclidine, orphenadrine) are mainly used for drug-induced parkinsonism or severe tremor in younger Parkinson's patients. Their use is limited by significant anticholinergic side effects, especially in the elderly (confusion, urinary retention, glaucoma exacerbation). They are generally not first-line for idiopathic Parkinson's.

SBAs frequently test the classic anticholinergic side effects ('dry as a bone, red as a beet, hot as a hare, blind as a bat, mad as a hatter'). Questions may also focus on their specific utility for tremor in Parkinson's disease or their role in drug-induced parkinsonism. The contraindications, especially in the elderly, are high-yield.