NEW ORLEANS — The novel antiarrhythmic agent RSD1235 effectively converted atrial fibrillation to sinus rhythm in a median of just 11 minutes in its initial phase III clinical trial, Dennis Roy, M.D., reported at the annual meeting of the Heart Rhythm Society.
The drug's safety profile also was excellent. There were fewer significant adverse events than with placebo—and most importantly, no cases of torsade de pointes, added Dr. Roy of the Montreal Heart Institute.
RSD1235 is a frequency-dependent sodium and early-activating potassium channel blocker with multiple electrophysiologic effects. It is atrial selective, with no effect upon ventricular repolarization, a highly desirable property in a drug for the treatment of atrial arrhythmias.
Dr. Roy reported on 336 patients with atrial fibrillation of 3 hours' to 45 days' duration who were randomized 2:1 to RSD1235 or placebo in the double-blind Atrial Arrhythmia Conversion Trial 1 (ACT 1). Patients who didn't convert within 15 minutes after completion of the initial IV infusion of 3 mg/kg given over 10 minutes received a second one, this time at 2 mg/kg.
The primary end point in ACT 1 was conversion to sinus rhythm within 90 minutes of treatment in the 220 patients with atrial fibrillation of up to 7 days' duration. The rate was 52% in the RSD1235 group, compared with just 4% with placebo. Only 1 of the 75 RSD1235-treated patients who converted within 90 minutes relapsed by 24 hours.
It is clearly a drug for recent-onset patients. The conversion rate in subjects with atrial fibrillation of 8–45 days' duration was 8% with RSD1235 and 0% for placebo.
The chief side effect associated with RSD1235 was impairment of taste, or dysgeusia, which affected 30% of treated patients but lasted an average of only 12 minutes. Second most common were sneezing fits, which affected 16% of patients and lasted 3 minutes, followed by paresthesia, affecting 11% for an equally brief period. Recurrence of atrial fibrillation within 30 days occurred in 6% of the RSD1235 group.
Additional phase III trials known as ACT 2 and ACT 3 are well underway. They include patients with atrial flutter as well as those with atrial fibrillation arising after cardiac surgery.
Dr. Roy is a consultant to and equity holder in Cardiome Pharma Corp., the developer of RSD1235.
Elsewhere at the meeting, in a state-of-the-art talk on the prospects for new drugs for atrial fibrillation, Peter F. Kowey, M.D., called the results of ACT 1 encouraging. Also encouraging is the program to develop an oral formulation of RSD-1235 designed for long-term maintenance of sinus rhythm following conversion of atrial fibrillation.
Many other drugs in development show varying degrees of promise. These include the atrial-selective agent AZD7009, gap junction modulators designed to restore pathologic defects in intercellular conduction, 5-hydroxytryptamine antagonists such as piboserod, and ATI-2042, a structural analog of amiodarone with similar electrophysiologic effects but less toxicity.
There is a great need for new agents for atrial fibrillation because the vast majority of affected patients will never be candidates for invasive catheter ablation procedures. And most of them would prefer to be on effective rhythm- than rate-control medications, said Dr. Kowey, professor of medicine at Jefferson Medical College, Philadelphia.
He couldn't resist the opportunity to toss a few zingers at colleagues in the ablation camp.
“For some reason, when ablationists get up and talk about what's happening in atrial fibrillation, they always tell us, 'Yeah, it's not so good right now, but it's going to get a whole lot better—and by the way, drugs suck.' Nobody gives the people on the drug side credit for the fact that, gee, we might get better, too. I mean, we're not exactly sitting on our hands here,” he said.
“There's a tremendous amount of activity going on in the drug development world to understand the arrhythmia mechanisms better, which the ablationists don't seem to really care as much about, and also to try to find specific probes to treat those arrhythmias using new chemical entities that are not only more effective but safer,” Dr. Kowey added.