Already commonly used in combination for the treatment of pulmonary arterial hypertension (PAH), macitentan and tadalafil are safe and effective in a fixed-dose combination even as first-line therapy, according to a randomized multicenter comparative trial.
The fixed-dose combination “led to a highly significant and marked improvement in pulmonary vascular resistance when compared to macitentan and tadalafil as monotherapies,” Kelly Chin, MD, reported at the joint scientific sessions of the American College of Cardiology and the World Heart Federation.
Guidelines encourage rapid PVR reductions
In practice, it is common to start treatment with either the endothelial receptor antagonist (ERA) macitentan, the phosphodiesterase-5 (PDE-5) inhibitor tadalafil, or other frequently used medications for PAH, and to then add additional treatments, according to Dr. Chin. She pointed out, however, that guidelines, including those issued jointly by the European Society of Cardiology and the European Respiratory Society, encourage rapid escalation of therapy to quickly lower pulmonary vascular resistance (PVR).
In general, both macitentan and tadalafil are well tolerated, but the advantage and the safety of rapidly reducing PVR when these are initiated together in a single pill had not been evaluated previously in a major trial. In this double-blind phase III trial, called A DUE, 187 patients in functional class II or III PAH were randomized. The three-arm study included both treatment naive patients and patients who had been on stable doses (> 3 months) of an ERA or a PDE5 inhibitor, explained Dr. Chin, director of pulmonary hypertension at the UT Southwestern, Dallas.
Treatment naive patients, representing about 53% of the study population, were randomized to 10 mg macitentan monotherapy, 40 mg tadalafil monotherapy, or a fixed-dose, single-pill combination containing both. If on a stable dose of an ERA at trial entry, patients were randomized to 10 macitentan as a monotherapy or to the fixed dose combination. Patients entering the trial already on a stable dose of a PDE5 inhibitor were randomized to 40 mg tadalafil or the combination.
PVR reduced twofold on combination therapy
Relative to macitentan monotherapy, the percentage change from baseline in PVR by ratio of geometric mean, which was the primary outcome, was about twice as high on the combination (45% vs. 23%) at the end of the 16-week trial. This translates into a 29% PVR reduction (hazard ratio, 0.71; P < .0001).
For combination therapy relative to tadalafil monotherapy, the advantage for the fixed dose combination (44% vs. 22%) was about the same, also providing a nearly 30% relative reduction (HR, 0.72; P < .0001).
The increases in 6-minute walk distance (6MWD) at 16 weeks, a secondary endpoint, numerically favored the combination pill over both macitentan monotherapy (52.9 vs. 39.5 meters; P = .38) and tadalafil (43.4 vs. 15.9 meters; P = .059), but only the improvement relative to tadalafil monotherapy was considered a trend.
The proportion of patients who experienced at least one serious adverse event was higher in the combination arm (14.0%) relative to single agent macitentan (8.6%) or single agent tadalafil (9.1%). The adverse events and serious adverse events more common on the combination included hypotension, fluid retention, and anemia. This latter side effect occurred in 18.7%, 2.9%, and 2.3% in the combination, macitentan monotherapy, and tadalafil arms, respectively.
Several of those invited by the ACC to discuss the paper, including Lee R. Goldberg, MD, section chief of advanced heart failure and cardiac transplant, University of Pennsylvania, Philadelphia, raised concern about the increased rate of anemia among those in the combination pill. Two of the patients (2%) treated with the combination developed a hemoglobin < 8 g/dL.
Overall, nine (8.4%) of those on the fixed-dose combination, two (4.5%) of those randomized to tadalafil monotherapy, and none of the patients randomized to macitentan discontinued therapy due to side effects.
Anemia risk unexpected
Based on “the unexpected signal of an anemia risk,” Biykem Bozkurt, MD, PhD, chair of cardiology at Baylor College of Medicine, Houston, said that a larger scale trial with a longer follow-up is needed. While the concept of front-loading two drugs is attractive “for the very challenging PAH population,” she called for further evaluation of this safety signal before clinicians switch from the current practice of starting with one PAH therapy before adding others.
In addition, Dr. Bozkurt said a more definitive study would be helpful in determining whether starting with a fixed-pill combination is better than sequential treatment to improve quality of life. Dr. Bozkurt said it is likely that the lack of significant benefit on 6MWD in this study was due to the relatively small sample size, but an improvement in this measure would be another reason to consider a front-line fixed-dose combination.
Dr. Chin, in an interview, did not agree. She agreed that a larger sample size might have yielded a significant improvement in 6MWD, but she noted this outcome was moving in the right direction and was not the primary endpoint. In her opinion, this phase 3 trial does confirm that fixed-dose combination is well tolerated, has acceptable safety, and markedly improves PVR, fulfilling the guideline goal of controlling PAH more quickly.
Dr. Chin reports financial relationships with Altavant, Arena, Gossamer Bio, Janssen, Merck, ShouTi, and United Therapeutics. Dr. Goldberg reports financial relationships with Abbott, Respicardia/Zoll, and Viscardia. Dr. Bozkurt reports financial relationships with Abbott, Amgen, AstraZeneca, Boehringer Ingelheim, Cardurion, LivaNova, Relypsa, Renovacor, Sanofi-Aventis, and Vifor.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.
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