Donanemab's limited-duration treatment paradigm is reshaping the lifetime cost calculation against lecanemab

Signal

The two FDA-approved anti-amyloid antibodies have structurally different treatment protocols. Donanemab (Kisunla, Lilly) is dosed every four weeks until amyloid clearance is achieved on PET imaging - in the TRAILBLAZER-ALZ 2 trial, this occurred in roughly half the cohort by 12 months and the majority by 18 months. Treatment then stops. Lecanemab (Leqembi, Eisai/Biogen) is dosed every two weeks at 10 mg/kg indefinitely, with no protocol-defined stopping point and continuation rationale tied to ongoing slowing of decline.

Annual list price is roughly comparable - lecanemab around USD 26,500 per year, donanemab around USD 32,000 per year for 12 months of treatment. But the lifetime arithmetic diverges meaningfully. A patient on donanemab who achieves clearance at 18 months has incurred approximately USD 48,000 in drug cost. The same patient on lecanemab over a 10-year continuation period would incur approximately USD 265,000.

Why it matters

For payers, the limited-duration paradigm is substantially more attractive on a per-patient lifetime basis, even though donanemab's higher annual price disadvantages it on a budget-impact basis in the early treatment period. The conversation has shifted from headline annual cost to total cost of treatment over a defined period.

For Eisai/Biogen, the response has been a sustained argument that continuous dosing is more clinically appropriate - cumulative slowing of decline correlates with cumulative dosing, and the natural-history risk after discontinuation is unknown. The OLE (open-label extension) data through 2025 has been Eisai's primary commercial counter-narrative.

For Lilly, the strategic position is that limited-duration treatment expands the patient pool that can plausibly access anti-amyloid therapy by reducing total cost exposure. In any market with budget caps - the UK and Germany particularly - this argument has more weight than in the US commercial market.

What we are watching

• The next round of long-term follow-up data from both products - any divergence in clinical outcomes between continuous and limited-duration cohorts will reshape the commercial argument.
• HTA-body framing in NICE, IQWiG, and other European HTA settings, where the limited-duration model materially changes the cost-effectiveness calculation.
• Real-world treatment-discontinuation patterns on lecanemab. If real-world dropout from continuous treatment runs higher than trial protocols would suggest, the difference between the two products' lifetime cost narrows.
• Whether either company shifts to mandatory clearance-based stopping rules under payer pressure. Donanemab's protocol already supports it; lecanemab's would require label or guideline change.