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 250mg, evening dose 125mg on day 1, maintenance dose 125mg twice daily; group B - test dose 500mg, placebo evening dose, maintenance dose 125mg twice daily; placebo group - placebo test and maintenance dose. Maintenance dosing was for 9 days. QTcF >550ms at any time during the in-patient phase or >500ms 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 >550ms. 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].

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