Rivastigmine

Indications

• FDA-approved for mild to moderate dementia of the Alzheimer type as capsules or patch, with the 13.3 mg/24 h patch also approved for severe disease.
• FDA-approved for mild to moderate dementia associated with Parkinson disease, the only cholinesterase inhibitor carrying that indication.
• Widely used off-label for dementia with Lewy bodies, where the cholinergic deficit is profound and visual hallucinations may improve.
• Average benefit is modest, on the order of 2-3 points on the ADAS-cog, with the practical goal being slower functional decline.
• Not indicated for mild cognitive impairment; cholinesterase inhibitors do not prevent or delay conversion to dementia.
• The patch is generally preferred over capsules because gastrointestinal tolerability and caregiver-supported adherence are both better.

Mechanism of action

• Pseudo-irreversible carbamate inhibitor of both acetylcholinesterase and butyrylcholinesterase in the central nervous system.
• Butyrylcholinesterase inhibition separates it from donepezil and galantamine and may matter more as Alzheimer disease advances.
• Raises synaptic acetylcholine in cortex and hippocampus, partially compensating for loss of basal forebrain cholinergic neurons.
• Carbamylation of the enzyme sustains inhibition for roughly 10 h even though the drug itself clears from plasma within hours.
• Peripheral cholinergic stimulation produces the nausea, vomiting, diarrhea, bradycardia and urinary urgency that limit dosing.

Pharmacokinetics

• Oral bioavailability is about 36% at 3 mg; food slows absorption and lowers peak levels, which is why capsules are taken with meals.
• Plasma half-life is only 1-2 h, but the duration of cholinesterase inhibition is far longer at roughly 10 h after a dose.
• Cleared by cholinesterase-mediated hydrolysis to a decarbamylated metabolite with minimal CYP450 involvement, so CYP interactions are few.
• Metabolites are excreted renally and protein binding is low at about 40%, leaving little room for displacement interactions.
• The patch produces smoother concentrations with a lower peak and comparable total exposure, which is the basis of its better tolerability.

Dosing

• Capsules: start 1.5 mg twice daily with food and increase by 1.5 mg twice daily at intervals of at least 2 weeks; the maximum is 6 mg twice daily.
• Patch: start 4.6 mg/24 h, step up to the usual effective 9.5 mg/24 h after at least 4 weeks, and to 13.3 mg/24 h in severe Alzheimer disease.
• Switching from capsules: under 6 mg daily goes to the 4.6 mg patch and 6-12 mg daily goes to the 9.5 mg patch, applied the day after the last capsule.
• If therapy is interrupted for more than 3 days, restart at the lowest dose and re-titrate, since resuming at the old dose causes severe vomiting.
• Apply one patch only, to clean dry hairless skin on the upper back, chest or upper arm, rotating sites and avoiding the same site for 14 days.
• Consider lower maintenance doses in patients under 50 kg and in mild to moderate renal or hepatic impairment, where exposure rises.

Adverse effects

• Oral therapy causes nausea in up to 47% and vomiting in about 31%, the worst gastrointestinal profile of the cholinesterase inhibitors.
• The patch cuts nausea to roughly 7-10% but adds application-site erythema and pruritus, occasionally true allergic contact dermatitis.
• Anorexia and clinically meaningful weight loss are common, and a documented fall in weight is a legitimate reason to stop the drug.
• Bradycardia, syncope, sinoatrial and atrioventricular block can occur and contribute to falls and hip fracture in frail patients.
• Increased gastric acid secretion raises ulcer and gastrointestinal bleeding risk, particularly alongside NSAIDs or anticoagulants.
• Seizures, worsening bronchospasm in asthma or COPD, and urinary outflow symptoms are less common but clinically important.

Monitoring

• Weight at every visit, since anorexia and weight loss are the commonest reasons treatment fails in this population.
• Pulse and orthostatic blood pressure at baseline and after each increase, with an ECG if there is syncope, bradycardia or conduction disease.
• Cognitive and functional measures such as MMSE, MoCA or an activities-of-daily-living scale every 6 months to justify continuation.
• Inspect patch application sites for spreading erythema or vesicles, which suggest contact allergy and preclude oral rechallenge.
• Review the anticholinergic burden at each visit, because coprescribed oxybutynin or diphenhydramine directly cancels the benefit.

Interactions

• Anticholinergic drugs including oxybutynin, diphenhydramine, tricyclics and paroxetine pharmacologically oppose the effect and should be deprescribed.
• Additive bradycardia occurs with beta blockers, digoxin, diltiazem, verapamil and amiodarone, and can precipitate syncope and falls.
• Exaggerated neuromuscular blockade follows succinylcholine, so anesthesia teams must be told the patient is on a cholinesterase inhibitor.
• NSAIDs combined with increased gastric acid secretion raise the risk of peptic ulceration and gastrointestinal hemorrhage.
• Because clearance is not CYP-mediated, CYP interactions are negligible, though smoking increases rivastigmine clearance by roughly a quarter.

Special populations

• Pregnancy and lactation: no human data and no indication in this age group, so use is essentially never appropriate.
• Pediatric safety and effectiveness have not been established and there is no approved use in patients under 18 years.
• Geriatric patients are the target population; the practical limits are weight loss, bradycardia, syncope and falls rather than cognition.
• Renal or hepatic impairment raises exposure substantially, so use lower maintenance doses and titrate more slowly in mild to moderate disease.
• Body weight under 50 kg predicts more nausea, vomiting and weight loss, and often calls for a lower target dose than the label maximum.

Clinical pearls

• The patch causes far less nausea than capsules; 9.5 mg/24 h is the usual effective dose.
• Off the drug more than 3 days? Re-titrate from the start or expect violent vomiting.
• It is the only cholinesterase inhibitor approved for Parkinson disease dementia.