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Centre for Evidence-
Based Medicine

Completed Therapy Worksheet for Evidence-Based General Practice

Citation

Schoenen J, Jacquy J, Lenaerts M. Effectiveness of high-dose riboflavin in migraine prophylaxis. A randomised controlled trial. Neurology. 1998; 50: 466-70.

Are the results of this single preventive or therapeutic trial valid?

  1. Was the assignment of patients to treatments randomised?
    And was the randomisation list concealed?
    Yes
  2. Were all patients who entered the trial accounted for at its conclusion?
    And were they analysed in the groups to which they were randomised?
    Yes.
    1 patient was excluded from analysis for a protocol violation.
  3. Were patients and clinicians kept "blind" to which treatment was being received?
    Yes - the trial used a placebo identical to the riboflavin
  4. Aside from the experimental treatment, were the groups treated equally?
    Yes - again the use of placebo helped control co-intervention.
  5. Were the groups similar at the start of the trial?
    Yes

Are the valid results of this randomised trial important?

Sample Calculations

Occurrence of diabetic neuropathy Relative Risk Reduction
RRR
Absolute Risk Reduction
ARR
Number Needed to Treat
NNT
Usual Insulin
Control Event Rate
CER
Intensive Insulin
Experimental Event Rate
EER
(CER - EER)/CER CER - EER 1/ARR
9.6% 2.8% (9.6% - 2.8%)/9.6%
= 71%
9.6% - 2.8%
= 6.8%
1/6.8%
= 15 pts

95% Confidence Interval (CI) on an NNT
= 1 / (limits on the CI of its ARR)
= +-1.96 sqrt(((CERx(1-CER))/(# of control pts.)) + ((EERx(1-EER))/(# of exper. pts.)))
= +-1.96 sqrt(((0.096x0.904)/730) + ((0.028x0.972)/711))
= ±2.4%

Your Calculations

< 50% improvement in migraine frequency at 3 months Relative Risk Reduction
RRR
Absolute Risk Reduction
ARR
Number Needed to Treat
NNT
CER EER (CER - EER)/CER CER - EER 1/ARR
81% 46% 43% 35% 3

Can you apply this valid, important evidence about a treatment in caring for your patient?

Do these results apply to your patient?

  1. Is your patient so different from those in the trial that its results can't help you?
    My patient had been having 4 migraines per month, and had had migraines for several years and so fulfilled the criteria.
  2. How great would the potential benefit of therapy actually be for your individual patient?
    She'd expect to reduce the frequency from 4 to about 2 per month.
  3. Method I: f
    Risk of the outcome in your patient, relative to patients in the trial. expressed as a decimal: _____

    NNT/F
    = ___ /___
    = (NNT for patients like yours)

Are your patient's values and preferences satisfied by the regimen and its consequences?

  1. Do your patient and you have a clear assessment of their values and preferences?
    Taking riboflavin once per day would be worth avoiding 2 migraines per month.
  2. Are they met by this regimen and its consequences?

Additional Notes

The reduction in migraine frequency appeared to develop over the 3 months. Patients should not expect an immediate reduction. Riboflavin is available as a sole ingredient (not as a multivitamin) but costs around $10 per month.

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