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?