Effects of pioglitazone on risks for cardiovascular events and diabetes in patients with prediabetes and a history of stroke or transient ischemic attack
By Aly Becraft, MS and Kevin C Maki, PhD
Insulin resistance is an established risk factor for stroke and other adverse cardiovascular events.1,2 As many as 50% of patients with stroke or transient ischemic attack have insulin resistance without being classified as having diabetes.3 Furthermore, insulin resistance is associated with cardiovascular risk factors such as increased blood pressure, elevated levels of triglycerides and inflammatory markers and reduced high-density lipoprotein concentration.4 Pioglitazone is an insulin-sensitizing medication that works to lower insulin resistance by activating peroxisome proliferator-activated receptors (PPAR)-γ, and slightly activating PPAR-α, which have potential cardioprotective effects by promoting fatty acid uptake and oxidation.5-9 In the Insulin Resistance Intervention After Stroke (IRIS) trial, pioglitazone was shown to reduce the risk of stroke or myocardial infarction (MI) by 24% compared to placebo in patients with insulin resistance and a history of stroke or transient ischemic attack.10 Treatment with pioglitazone also reduced new-onset diabetes by half.10
Spence and colleagues published a post-hoc analysis of the IRIS trial to investigate the effect of pioglitazone in those patients with good adherence (taking ≥80% of the protocol dose over the duration of the study) and with prediabetes defined using the American Diabetes Association (ADA) definition.11 In the IRIS trial, patients were enrolled based on their homeostasis model assessment of insulin resistance (HOMA-IR) score,10 which is not routinely measured in clinical practice, whereas the ADA definition considers patients to have prediabetes if their glycated hemoglobin (HbA1c) level is 5.7-6.4% or fasting plasma glucose level is 100-125 mg/dL. The primary outcome was recurrent fatal or nonfatal stroke or myocardial infarction. Secondary outcomes included stroke; acute coronary syndrome; the composite of stroke, MI, hospitalization for heart failure; and the progression to diabetes.
In the IRIS trial, patients were randomized to receive either 15 mg/d pioglitazone titrated up to a maximum dose of 45 mg/d, or a matched placebo. In this analysis, 2885 of the 3876 participants enrolled in the IRIS trial were classified as have prediabetes; 1456 were in the pioglitazone group and 1429 in the placebo group. Among these, 1454 were also classified as having good adherence; 644 were in the pioglitazone group and 810 were in the placebo group. Median follow-up time was 4.8 years.
In those patients with ADA-defined prediabetes and good adherence, the relative risk reductions (RRR) with pioglitazone vs. placebo were 40% for stroke + MI, 33% for stroke, 52% for acute coronary syndrome, and 38% for stroke + MI + hospitalization for heart failure. The relative risk for new-onset diabetes was also reduced by 80% for pioglitazone vs. placebo. Adverse events in the pioglitazone group included weight gain of ≥10% of body weight (29.8% vs. 12% in placebo group; p < 0.001), edema (29.2% vs. 21.6% in placebo group; p < 0.001), and serious bone fractures (3.6% vs. 2.8% in placebo group; p = 0.08). These adverse effects were also observed in the full IRIS trial analysis.12
Comment: An initial requirement of enrollment in the IRIS trial was HOMA-IR score ≥3; therefore, the findings from this trial can only be extended to patients with prediabetes that meet this criterion. That said, this post-hoc analysis provides evidence that patients with prediabetes and established stroke or transient ischemic attack have improved clinical outcomes when treated early, particularly when adherence to treatment is high. Edema was a large contributor to weight gain observed with pioglitazone treatment, which may be less with lower dosages than were used in this trial. For instance, a dose of 7.5 mg/d has been associated with low incidence of weight gain and edema.12 The IRIS investigators conclude that the benefit of pioglitazone treatment demonstrated in this and in the original analysis10 appear to outweigh the observed risks. Additional research is warranted to assess the effects of lower dosage pioglitazone therapy for cardiovascular risk reduction in a wider range of patients than were studied in IRIS.
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