Influence of age on the efficacy and safety of dabigatran versus warfarin for the treatment of acute venous thromboembolism: a pooled analysis of RE-COVER and RE-COVER II

BACKGROUND:

In the RE-COVER and RE-COVER II trials, a fixed dose of dabigatran etexilate was as effective as warfarin for prevention of recurrent VTE and was associated with a lower risk of bleeding. It is not known whether this efficacy and difference in bleeding rates is maintained in older patients.

OBJECTIVES:

Older patients may be at greater risk of bleeding and/or VTE. Therefore, we performed a subgroup analysis on the pooled RE-COVER and RE-COVER II trial results to investigate the efficacy and safety of dabigatran versus warfarin for the treatment of acute VTE according to age.

METHODS:

Patients with acute VTE received parenteral anticoagulation and were randomized to the addition of warfarin or warfarin-placebo for at least 5 days until the international normalized ratio (INR) was ≥ 2 at two consecutive measurements. This was followed (on discontinuation of parenteral therapy) by continued warfarin (target INR range 2.0–3.0) or dabigatran 150 mg twice daily (double dummy; “oral only” treatment period) for 6 months. Outcomes were centrally adjudicated. The primary efficacy outcome was recurrent, symptomatic, objectively confirmed VTE or VTE-related death from randomization (i.e., start of parenteral therapy plus either warfarin or warfarin-placebo) up to the end of the prespecified post-treatment follow-up. Major bleeding events (MBEs), the composite of MBEs or clinically relevant non-major bleeding events (CRBEs), and any bleeds were counted from the start of the double-dummy period (treatment with oral dabigatran or warfarin alone) up to the end of the 6-month study period. Thus, the safety analysis excludes events associated with parenteral therapy either in combination with warfarin or with warfarin-placebo prior to commencing dabigatran treatment; it therefore compares dabigatran with warfarin at its full pharmacological potential.

RESULTS:

Of 2553 patients randomized to dabigatran, 68 (2.7%) had recurrent VTE or VTE-related death compared with 62 (2.4%) of 2554 patients randomized to warfarin; hazard ratio (HR) 1.09 (95% CI 0.77, 1.54). The incidences of the primary efficacy outcome (dabigatran vs warfarin) by age group were 3.0% (53/1769) versus 2.4% (42/1748) for patients < 65, 2.3% (12/531) versus 2.5% (13/530) for patients 65–75, and 1.2% (3/253) versus 2.5% (7/276) for patients > 75 years; and in a second age-group comparison were 2.8% (67/2418) vs 2.3% (57/2429) for patients < 80 and 0.7% (1/135) versus 4.0% (5/125) for patients ≥ 80 years. Cox regression analysis showed no statistically significant interaction, indicating that there are similar treatment effects across age groups. MBEs were significantly less frequent with dabigatran than with warfarin overall (HR 0.60; 95% CI 0.36, 0.99). Incidences by age group are shown in the Table. MBE/CRBE incidence was also significantly lower with dabigatran versus warfarin overall (HR 0.56; 95% CI 0.45, 0.71). The Table shows event rates for each age group. Similarly, any bleeding events were significantly less frequent with dabigatran than with warfarin overall. There was no significant treatment-by-age interaction for MBEs or MBEs/CRBEs or any bleeds in either analysis.

CONCLUSIONS:

No differences in recurrent VTE or efficacy were apparent across the age groups. Bleeding events increased with increasing age but numerically were similar or lower with dabigatran than with warfarin regardless of age. The results suggest there is no need for dose adjustment of dabigatran according to age for the treatment of VTE.