GPs’ decisions on drug therapies by number needed to treat Peder A. Halvorsen University of...

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?