GPs’ decisions on drug therapies
by number needed to treat
Peder A. HalvorsenUniversity of Tromsø, Norway
Torbjørn WisløffIvar Sønbø Kristiansen
University of Oslo, Norway
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
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
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
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?
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”
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
Research questions
• Are GPs sensitive to the magnitude of
NNT when considering statin therapy?
• Do GPs use NNT when explaining risk
reductions to patients?
Methods
• Subjects: 450 GPs in Norway
• Postal questionnaire survey
• Random allocation to three different
versions of the Mr Smith case
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
Would you recommend Neostatin for Mr Smith?
□ Certainly “Yes”
□ Probably
□ Probably not “No”
□ Certainly not
Rating scale: Is Neostatin good or bad?
What is your judgement of Neostatin as a prophylactic drug
against cardiovascular disease?
A very poor
choice0 1 2 3 4 5 6 7 8 9 10 A very good
choice
Results
NNT Proportion recommending
Neostatin
n = 214
Mean score
rating scale
n = 203
10
19
37
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
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
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
Results
• Qualitative terms only: 66 %
• Relative risk reduction: 21 %
• Absolute risk reduction: 24 %
• NNT 20 %
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.
Acknowledgments
Torbjørn WisløffHenrik Støvring
Ivar Sønbø KristiansenOdense Risk Group
(Naimark-D. J Gen Intern Med 1994; 9: 702-707)
Modelling life long treatment:
What NNT should we report?
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