Neurology/Parkinson's adjuncts (MAO-B / COMT)

Parkinson's adjuncts (MAO-B, COMT, antimuscarinic)

also: selegiline · rasagiline · entacapone · amantadine · procyclidine

Overview

Enzyme inhibitors and other adjuncts that extend levodopa's effect or target specific symptoms.

Mechanism

MAO-B inhibitors (selegiline/rasagiline) block central dopamine breakdown. COMT inhibitors (entacapone) block peripheral levodopa breakdown → prolong its action. Amantadine has weak dopaminergic + anti-glutamate (NMDA) effects (helps dyskinesia). Antimuscarinics (procyclidine) rebalance the dopamine/acetylcholine ratio (tremor, drug-induced parkinsonism).

Indications

Adjuncts in Parkinson's (reduce wearing-off)
Drug-induced parkinsonism / tremor (antimuscarinic)
Dyskinesia (amantadine)

The agents

Selegiline / rasagilineMAO-B inhibitor

Adjunct; avoid combining with serotonergics (serotonin syndrome).

EntacaponeCOMT inhibitor

with each levodopa dose

Reduces wearing-off; harmless reddish urine.

Amantadineanti-dyskinesia

Reduces levodopa-induced dyskinesia; livedo reticularis.

Procyclidineantimuscarinic

Tremor / drug-induced parkinsonism (avoid in elderly — confusion).

Adverse effects

MAO-B: serotonin syndrome with SSRIsserious

Antimuscarinic effects (confusion in elderly, dry mouth, retention)common

Amantadine: livedo reticularis, ankle oedema, hallucinationscommon

Cautions & contraindications

MAO-B inhibitor with serotonergic drugsall

Serotonin syndrome.

Antimuscarinics in elderly / cognitive impairmentelderly

Interactions

MAO-B + SSRIs/SNRIs/opioids; antimuscarinic burden

Monitoring & kinetics

Motor response; cognitive/psychiatric effects

Oral adjuncts to levodopa.

Source: NICE NG71 — Parkinson's · BNF — Parkinson's adjuncts