Average cost effectiveness
In a patient at 10% coronary risk over five years, aspirin is the most cost effective risk lowering treatment, at £3500 per coronary event prevented. Initial antihypertensive treatment costs £12 500, intensive antihypertensive treatment costs £18 300, clopidogrel costs £60 000, and simvastatin costs £61 400 per coronary event prevented ().
Average costs, effects, and cost effectiveness of preventive treatments in a patient at 10% risk of a coronary event over five years
In a sensitivity analysis I calculated the cost per event prevented for each intervention if its effectiveness was given by the upper and lower 95% confidence limits of the estimates (see ). The cost effectiveness of aspirin, initial antihypertensive treatment, and intensive antihypertensive treatment are sensitive to changes in assumptions about effectiveness. However, for simvastatin to be of similar cost effectiveness to intensive antihypertensive treatment, the relative risk with treatment must be at the lower 95% confidence interval and the cost of the drug 65% lower. This is unlikely, as drug prices typically fall by less than 50% when they come off patent. There is a wide degree of uncertainty about the cost effectiveness of clopidogrel, reflecting uncertainty about the relative risk on treatment.
Average cost effectiveness of preventive treatments in a patient at 10.5% risk of a coronary event over five years. (Error bars represent cost per coronary event prevented if effectiveness is at upper and lower 95% confidence limit)
Varying the discount rates for either costs or benefits from 0% to 10% has no effect on rankings. Using a general practitioner for follow up has no effect on cost effectiveness rankings. Cost effectiveness of initial and intensive antihypertensive treatment is sensitive to increases in the price of drugs. If sufficiently high cost drugs are used (such as for brand name calcium channel blockers) the cost per event prevented with initial antihypertensive drugs is as high as with a statin.
Incremental cost effectiveness of additional treatments
Costs of follow up clinic visits do not increase with extra treatments. The incremental costs of additional treatments therefore include only additional drug costs and additional laboratory investigations. The incremental effectiveness of additional drugs is also smaller than their effectiveness as initial treatments because incremental effects act on progressively smaller pretreatment risks.
If a patient at 10% five year coronary risk is given combination treatments in order of their cost effectiveness, the incremental cost per event prevented rises with each additional treatment. Compared with placebo, clopidogrel is more cost effective than simvastatin. However, clopidogrel as a replacement for aspirin provides little additional benefit at substantial extra cost. It is therefore the least cost effective in an incremental analysis. Incremental costs per event prevented are £3500 for aspirin, £12 000 for initial antihypertensive treatment, £33 900 for enalapril, £122 400 for simvastatin, and £527 200 for clopidogrel ().
Incremental costs of preventive treatments in combination per event avoided in a patient at 10% risk of a coronary event over five years
I carried out a sensitivity analysis to investigate the effects of varying the costs and effectiveness of treatments. The most favourable assumption for simvastatin is that relative risks for all other treatments are at the upper 95% confidence limit and for simvastatin is at the lower 95% confidence limit. If this is the case, the incremental costs per event prevented are £8700 for aspirin, £18 800 for initial antihypertensive treatment, £243 000 for intensive antihypertensive treatment, £65 800 for simvastatin, and £177 300 for clopidogrel. Even under these assumptions, the price of simvastatin would have to fall by 70%, and the price of clopidogrel by more than 90%, to be of similar cost effectiveness to initial antihypertensive treatment.
Under the base case analysis, the cost effectiveness rankings of all five treatments are the same for any patient with a five year coronary risk greater than 1.5%. The incremental cost per event prevented in a patient at 5% five year coronary risk is £7900 with aspirin and £24 000 with initial antihypertensive treatment. This is less than the incremental cost per event prevented with simvastatin (£40 800) in a patient at 30% five year coronary risk (see )
Incremental cost per event prevented of treating patients at a range of pretreatment risks of a coronary event over five years
The most extreme assumptions we can make are to assume that relative risk on all treatments is at the upper 95% confidence limit (least effective) and assume that the relative risk with simvastatin is at the lower 95% confidence limit (most effective). Under these assumptions, the cost per event prevented with aspirin in a patient at 7.5% five year risk would be £12 900 and the cost per event prevented with simvastatin in a patient at 15% five year risk would be £13 200.