GPs’ decisions on drug therapies by number needed to treat

1. GPs’ decisions on drug therapiesby number needed to treat Peder A. Halvorsen University of Tromsø, Norway Torbjørn Wisløff Ivar Sønbø Kristiansen University of Oslo, Norway

2. Mr Smith - Mr Smith (55) consults you for a check up on blood pressure and cholesterol because his father got a heart attack at age 52. - Mr Smith has no symptoms

3. Workup of the Mr Smith case Ten year risk of CVD: 20 out of 100 Ten year risk of death due to CVD: 8 out of 100

4. Neostatin • A new cholesterol lowering drug therapy • Randomized trials in primary care as well as hospitals. • Side effects similar to other statins • Cost per year: 1000 NOK

5. Neostatin • If groups of 19 people takes Neostatin for 20 years, one will observe 1 less patient with cardiovascular disease compared to no therapy. • Mr Smith has no clear preference for or against the drug and asks for your opinion. • Would you recommend Neostatin for Mr Smith?

6. NNT • NNT=1/ARR (absolute risk reduction) • ”The number of individuals that must be treated to prevent one adverse outcome” • “Intuitively meaningful and easy to understand”

7. Lay people are rather insensitive to NNTs: NNT patients must be treated for three years to prevent one adverse outcome. Would you chose to take such a drug? Halvorsen PA, Kristiansen IS. Archives of Internal Medicine 2005

8. Research questions • Are GPs sensitive to the magnitude of NNT when considering statin therapy? • Do GPs use NNT when explaining risk reductions to patients?

9. Methods • Subjects: 450 GPs in Norway • Postal questionnaire survey • Random allocation to three different versions of the Mr Smith case

10. Effect measures in the Mr Smith vignette NNT after 20 years of therapy* --------------------------------------------------------------------------------------------------- Group 1 9 Group 2 19 (simvastatin) Group 3 37 --------------------------------------------------------------------------------------------------- * Based on the NORCAD model of CVD disease in Norway

11. Would you recommend Neostatin for Mr Smith? □ Certainly “Yes” □ Probably □ Probably not “No” □ Certainly not

12. Rating scale: Is Neostatin good or bad? What is your judgement of Neostatin as a prophylactic drug against cardiovascular disease?

13. Results

14. Results Chi-square trend = 3.85 p = 0.05

15. Results Chi-square trend = 3.9 p = 0.05 ANOVA trend, F = 8.2 p = 0.005

16. Explaining risk reductions to patients How do you usually inform your patients about risk reducing drug therapies? □ In numerical terms □ In qualitative terms □ Both □ None of these/not applicable in my work

17. Results • Qualitative terms only: 66 % • Relative risk reduction: 21 % • Absolute risk reduction: 24 % • NNT 20 %

18. Conclusion • GPs were sensitive to the magnitude of NNT when considering a new lipid lowering drug • A minority of GPs would use NNT when explaining risk reductions to patients.

19. Acknowledgments Torbjørn Wisløff Henrik Støvring Ivar Sønbø Kristiansen Odense Risk Group

20. Modelling life long treatment: What NNT should we report? (Naimark-D. J Gen Intern Med 1994; 9: 702-707)