What is the equivalent dosing of Exelon (Rivastigmine) 1.5mg twice daily (bid) to Aricept (Donepezil)?

Equivalent Dosing: Exelon (Rivastigmine) 1.5mg BID to Aricept (Donepezil)

Exelon (rivastigmine) 1.5mg twice daily (3mg total daily) is a subtherapeutic dose that does not have a direct equivalent in donepezil, as this represents an early titration phase rather than a maintenance dose; if switching is necessary, start donepezil at 5mg once daily, which represents the standard initial therapeutic dose for Alzheimer's disease. 1

Understanding the Dosing Context

The rivastigmine dose of 1.5mg BID (3mg total daily) is below the therapeutic range and represents only an initial titration step. 2 This is critical to understand because:

• Rivastigmine therapeutic dosing ranges from 6-12mg daily, with the 9.5mg/24-hour patch being equivalent to approximately 6mg oral twice daily 2
• Your current dose of 3mg total daily is only 25-50% of the minimum therapeutic dose 2
• Inadequate rivastigmine dosing can lead to cholinergic withdrawal, manifesting as acute cognitive decline and behavioral symptoms 2

Why Direct Dose Conversion Is Not Appropriate

There is no established equivalency table for subtherapeutic doses between these medications because:

• Clinical trials establishing efficacy used therapeutic doses: rivastigmine 6-12mg daily and donepezil 5-10mg daily 3
• Rivastigmine at 6-12mg daily produces clinically meaningful improvements with moderate strength of evidence, while doses of 4mg daily or less show minimal benefit 2
• Donepezil's standard starting dose of 5mg once daily already represents a therapeutic dose, not a titration dose 1

Recommended Approach to Switching

If switching from rivastigmine 1.5mg BID to donepezil is clinically indicated, initiate donepezil at 5mg once daily in the evening, just prior to retiring. 1 This approach is justified because:

• The 5mg donepezil dose represents the evidence-based starting point for Alzheimer's disease treatment 1
• After 4-6 weeks, increase to donepezil 10mg once daily if well tolerated, as this dose provides superior efficacy 1
• Taking donepezil at bedtime rather than morning reduces sleep disturbances 1

Important Clinical Considerations

Before switching, strongly consider whether optimizing rivastigmine dosing is more appropriate than switching medications entirely. 2 The rationale includes:

• Rivastigmine has specific advantages for patients with hallucinations and rapid cognitive decline, including improved visual hallucinations in dementia patients 2
• Treatment interruption and inadequate dose conversion can lead to cholinergic withdrawal 2
• If the patient is on rivastigmine 1.5mg BID due to tolerability concerns, address these with food administration and slower titration rather than switching 2

Monitoring After Switch

If proceeding with the switch to donepezil:

• Monitor for cholinergic side effects including gastrointestinal symptoms (nausea, vomiting, diarrhea), with relative risk increasing at 10mg versus 5mg: nausea/vomiting RR 2.54, diarrhea RR 2.57, anorexia RR 3.21 1
• These effects can be minimized by taking donepezil with food and using gradual titration 1
• Assess for potential bradycardia (slow heart rate) and muscle cramps, particularly leg cramps 4
• Evaluate cognitive and functional status using caregiver reports and clinical assessment to assess treatment effectiveness 2

Common Pitfall to Avoid

Do not attempt a "dose-for-dose" conversion between 1.5mg BID rivastigmine and donepezil, as this subtherapeutic rivastigmine dose has no meaningful donepezil equivalent. The appropriate action is either: (1) optimize rivastigmine to therapeutic dosing (target 6mg BID or 9.5mg/24-hour patch), or (2) switch to standard-dose donepezil 5mg daily with planned uptitration to 10mg. 2, 1