QT response after a test dose and during maintenance therapy with AZD1305 in patients with atrial fibrillation: a double-blind, randomized, placebo-controlled trial.
BACKGROUND AND OBJECTIVE
AZD1305 is an investigational antiarrhythmic agent that prolongs refractoriness through combined potassium and sodium channel inhibition. This study aimed to explore the utility of a test dose in predicting QT interval corrected according to Fridericia's formula (QTcF) during subsequent maintenance treatment with AZD1305.


METHODS
This was a randomized, double-blind, parallel-group, placebo-controlled trial carried out at multiple hospital cardiac facilities in Denmark, Norway, Poland, Slovakia, and Sweden. Patients with documented atrial fibrillation (AF) but currently in stable sinus rhythm for ≥2 hours and ≤90 days were eligible for inclusion. Patients were randomized in a 1 : 1 : 1 ratio to receive AZD1305 extended-release or matching placebo tablets as follows: group A - test dose 250 mg, evening dose 125 mg on day 1, maintenance dose 125 mg twice daily; group B - test dose 500 mg, placebo evening dose, maintenance dose 125 mg twice daily; placebo group - placebo test and maintenance dose. Maintenance dosing was for 9 days. QTcF >550 ms at any time during the in-patient phase or >500 ms after discharge (day 4) were predefined study drug discontinuation criteria. The main outcome measure was the relationship between QTcF following the test dose and during maintenance treatment.


RESULTS
Sixty-five patients were randomized (n = 21, 22, and 22 in group A, group B, and the placebo group, respectively). AZD1305 dose-dependently increased QTcF. There was a positive, linear correlation between the change in QTcF during the first 6 hours after the test dose and during the maintenance phase. Three patients, all from group B, discontinued treatment on day 1 due to QTcF >550 ms. All other patients completed the study without events related to QT prolongation. There was a trend for reduced AF recurrence with AZD1305 compared with placebo.


CONCLUSION
In this exploratory study a test dose predicted the QT response during maintenance treatment with AZD1305 and may thus be employed in further studies. [ClinicalTrials.gov Identifier: NCT00643448].