Mepolizumab shows promise against hypereosinophilic syndrome

Mepolizumab, a humanized monoclonal antibody that binds interleukin-5, can suppress flares in patients with hypereosinophilic syndrome (HES) without posing new safety concerns, reports a recent trial.

Researchers randomly assigned HES patients to receive either 300 mg of subcutaneous mepolizumab (n=54; mean age, 46.6 years) or placebo (n=54; mean age, 45.4 years). Study interventions were given every 4 weeks for 32 weeks. The primary endpoint was the proportion of patients who had experienced a flare over the study duration.

Forty-two patients experienced 65 flares over the duration of the study. The occurrence of at least one episode of flares was twice as frequent in placebo participants than in their mepolizumab counterparts (56 percent vs 28 percent; p=0.002).

Logistic regression analysis verified this, showing a significantly suppressed risk of flares among the mepolizumab-treated participants (odds ratio [OR], 0.28, 95 percent confidence interval [CI], 0.12–0.64; p=0.003). This effect was robust to sensitivity and posthoc analyses.

In terms of secondary endpoints, Kaplan-Meier estimates showed that the likelihood of experiencing a first flare episode during the treatment period was reduced by 66-percent in the mepolizumab arm (hazard ratio, 0.34, 95 percent CI, 0.18–0.67; p=0.002). Similarly, the adjusted annualized rate of flares was also 66-percent lower in mepolizumab patients (p<0.001), who also saw greater improvement in fatigue severity at 32 weeks compared with placebo participants (p=0.04).

These intervention efficacies did not come with additional safety signals. While the prevalence of on-treatment adverse events was high, rates did not vary between groups (89 percent vs 87 percent). Drug-related side effects were also only modestly more common in the mepolizumab group (22 percent vs 13 percent).