PEBC MCQ Evidence-based Practice & Drug Information question: patients taking a mineralocorticoid receptor antagonist

PEBC MCQEvidence-based Practice & Drug Information

In a 12-week trial, clinically significant hyperkalemia occurred in 6% of patients taking a mineralocorticoid receptor antagonist and in 2% of those taking placebo. What is the number needed to harm over 12 weeks?

a. 17
b. 25
c. 33
d. 50

Show the answer and explanation

Answer: b. 25

The absolute risk increase is 6% - 2% = 4% (0.04), and the number needed to harm (NNH) is its reciprocal: 1/0.04 = 25. One extra patient develops hyperkalemia for every 25 treated for 12 weeks. The value 17 inverts the treatment-group rate alone (1/0.06), and 50 inverts the placebo rate (1/0.02), neither of which compares the groups. Source: Straus SE et al. Evidence-Based Medicine: How to Practice and Teach EBM, 5th ed. (Elsevier, 2018), ch. 4 Therapy; Guyatt G et al. Users' Guides to the Medical Literature, 3rd ed. (2015).

Common mistake

Taking the reciprocal of the event rate in one arm instead of the difference between arms.

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