GPs

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
Glucose 4.3
EKG Normal
BMI Hip waist ratio Physical fitness 24.5 1.1 Above average
Smoking No
Blood pressure 156/98
Total cholesterol LDL HDL Triglycerides 8.1 6.1 1.1 2.0
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

• NNT1/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 Yes
50 76
100 71
200 70
400 71
800 68
1600 67
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?

A very poor choice 0 1 2 3 4 5 6 7 8 9 10 A very good choice
13
Results
NNT Proportion recommending Neostatin n 214 Mean score rating scale n 203
10
19
37
14
Results
NNT Proportion recommending Neostatin n 214 Mean score rating scale n 203
10 80
19 74
37 66
Chi-square trend 3.85 p 0.05
15
Results
NNT Andel som ville anbefale Neostatin n 214 Mean score rating scale n 203
10 80 6.0
19 74 5.6
37 66 4.8
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)