Implementing the number needed to harm in clinical practice: risk of myocardial infarction in HIV‐1‐infected patients treated with abacavir

Abstract

ObjectivesThe D:A:D study group reported a 1.9-fold increased relative risk (RR) of myocardial infarction (MI) associated with current or recent use of abacavir. The number needed to harm (NNH) incorporates information about the underlying risk of MI and the increased RR of MI in patients taking abacavir. MethodsNNH was calculated as the reciprocal of the difference between the underlying risks of MI with and without abacavir use. A parametric statistical model was used to calculate the underlying risk of MI over 5 years. ResultsThe relationship between NNH and underlying risk of MI is reciprocal, resulting in wide variation in the NNH with small changes in underlying risk of MI. The smallest changes in NNH are in the medium-and high-risk groups of MI. The NNH changes as risk components are modified; for example, for a patient who smokes and has a systolic blood pressure (sBP) of 160 mmHg and a 5-year risk of MI of 1.3% the NNH is 85, but the NNH increases to 277 if the patient is a nonsmoker and to 370 if sBP is within the normal range (120 mmHg). ConclusionsWe have illustrated that the impact of abacavir use on risk of MI varies according to the underlying risk and it may be possible to increase considerably the NNH by decreasing the underlying risk of MI using standard of care interventions, such as smoking cessation or control of hypertension.Keywords: abacavir, antiretroviral treatment, myocardial infarction, number needed to harm Accepted 21 July 2009Introduction Abacavir is a common antiretroviral used in the treatment of HIV-1 infection and is currently recommended as one of the possible components of initial combination antiretroviral treatment [1][2][3]. The D:A:D study group recently reported an increased risk of myocardial infarction (MI) related to current or recent use of abacavir [4,5]. Some of the HIV-1 treatment guidelines have already taken into account the clinical implications of the D:A:D findings by emphasizing that clinicians should consider careful assessment of patients who are on abacavir and at high risk of MI [2,6,7]. It is therefore of great importance to ensure that the risk of MI attributed to abacavir use, together with the underlying risk of MI, is correctly interpreted and understood.Presenting results as relative risks (RRs) is standard in observational studies [8], but may be difficult to translate into clinical practice. The number needed to treat (NNT) and absolute risk reduction may be more clinically relevant, when assessing the beneficial effect of treatment [9][10][11], and the number needed to harm (NNH), together with absolute risk increase (ARI), will better reflect any adverse effect of treatment than RR in clinical terms [12]. Both NNH and RR are measures that attempt to summarize two numbers (the risks of MI with and without abacavir). RR summarizes the relative increase in the underlying risk DOI: 10.1111/j.1468-1293.00763.x HIV Medicine (2010 r 2009 British HIV Association 200of an event according to whether the patient receives a given treatment or not and the...

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