EURIDIS included 612 patients and ADONIS included 629 patients, all of whom at the time of randomization had been in sinus rhythm for at least one hour and had had at least one ECG-documented atrial fibrillation in the previous three months. Patients received either dronedarone 400 mg twice daily or placebo and were treated for 12 months.

The primary end point of both studies was the time from randomization to the first documented AF/AFL recurrence, defined as an episode lasting for 10 minutes or more as indicated by two consecutive 12-lead ECGs or transtelephonic ECG monitoring (TTEM) tracings recorded approximately 10 minutes apart and both showing AF/AFL.

Secondary end points were the mean ventricular rate during AF/AFL at the first recurrence and AF/AFL-rated symptoms at the time of ECG/TTEM.

The median time from randomization to a first adjudicated recurrence of AF/AFL was 2.3 times longer in the dronedarone group than in the placebo group in EURIDIS and almost three times longer in ADONIS.

Dronedarone significantly lowered the risk of first recurrence of AF/AFL within the 12-month study period by 22% compared with placebo (log-rank test p=0.0138) in EURIDIS and 28% in ADONIS (p=0.017)

Dronedarone also showed good tolerability, Hohnloser said. There was no cardiac toxicityno excess of congestive heart failure or any cases of torsades de pointesand no evidence of amiodaronelike toxicity such as thyroid or pulmonary problems. Overall, the incidence of adverse reactions was similar in the dronedarone group to the placebo group.

"There was a good consistency of efficacy and safety in the two studies," Hohnloser noted.

But in his discussion, Schalij said that, overall in the two trials, there was a cumulative recurrence rate of AF/AFL of 77% with placebo and 66% with dronedarone, "which seems disappointing."

"This may not be the wonder drug we are waiting for," he commented.

This may not be the wonder drug we are waiting for.

Also, "we don't know anything about the long-term side effects of this drug," he said, adding that some pulmonary effects had been seen with dronedarone in animal studies.

But in a Sanofi press conference, Dr Bramah N Singh (University of California, Los Angeles Medical School) said, "I thought the discussant was wrong about the toxicity." Obviously, longer-term data on dronedarone are needed, he conceded, but "I've been working with amiodarone for 30 years now, and certain side effectssuch as those on the thyroidare seen very early in the course of treatment."

Speaking to heartwire about the discussant's comments, Hohnloser said, "I wouldn't call dronedarone a wonder drug, but it's not disappointing. It's unlikely we will ever have a wonder drug for atrial fibrillation."

It's unlikely we will ever have a wonder drug for atrial fibrillation.

He added: "This drug may be able to be given on an outpatient basis. Also, the time interval to first recurrence of AF/AFL was increased twofold in EURIDIS and almost threefold in ADONIS. A patient cares about thisit makes a huge difference in clinical terms."

Sanofi Aventis is discussing dronedarone with both European and US regulatory authorities but has not yet filed the drug for approval.