Pharmacoeconomic Analysis of Two Antihypertensive Strategies
A health insurer is comparing two strategies for managing hypertension in a population of 10,000 patients. Strategy A: generic hydrochlorothiazide (HCTZ) 25 mg daily, cost €0.10 per day. Strategy B: branded amlodipine 5 mg daily, cost €1.50 per day. Both have similar efficacy in blood pressure reduction, but amlodipine has fewer side effects (less hypokalemia and gout) and better adherence. The insurer estimates that with HCTZ, 5% of patients will require additional treatment for hypokalemia (cost €200 per year) and 2% will develop gout (cost €500 per year). With amlodipine, these rates are 1% and 0.5%, respectively. Assume all patients are treated for 1 year.
1. Calculate the annual cost per patient for each strategy, including medication and adverse event management costs.
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Strategy A (HCTZ):
- Medication cost: €0.10/day × 365 = €36.50 per year.
- Hypokalemia cost: 5% × €200 = €10 per patient per year.
- Gout cost: 2% × €500 = €10 per patient per year.
- Total per patient = €36.50 + €10 + €10 = €56.50.
Strategy B (amlodipine):
- Medication cost: €1.50/day × 365 = €547.50 per year.
- Hypokalemia cost: 1% × €200 = €2 per patient per year.
- Gout cost: 0.5% × €500 = €2.50 per patient per year.
- Total per patient = €547.50 + €2 + €2.50 = €552.00.
So Strategy A costs €56.50 per patient per year, Strategy B costs €552.00 per patient per year.
2. Calculate the incremental cost per adverse event avoided when switching from HCTZ to amlodipine, and discuss the implications.
Read the worked answer
Incremental cost = €552.00 - €56.50 = €495.50 per patient per year.
Adverse events avoided:
- Hypokalemia: 5% - 1% = 4% absolute reduction, so 0.04 events avoided per patient per year.
- Gout: 2% - 0.5% = 1.5% absolute reduction, so 0.015 events avoided per patient per year.
- Total adverse events avoided per patient = 0.04 + 0.015 = 0.055 events per patient per year.
Incremental cost per adverse event avoided = €495.50 / 0.055 ≈ €9,009 per adverse event avoided.
This is very high; amlodipine is not cost-effective solely on this basis unless the adverse events have more severe long-term consequences or if adherence and BP control differences lead to cardiovascular event reductions. The insurer should consider other factors like patient quality of life and long-term outcomes.