The Pharmaceutical Journal
Vol 279 No 7474 432
20 October 2007

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Mixed results for factor X inhibitor as VTE treatment

Idraparinux — a long-acting inhibitor of activated factor X — has been tested in venous thromboembolism with mixed results.

Patients with deep-vein thrombosis (DVT; n=2,904) and pulmonary embolism (PE; n=2,215) received, for three or six months depending on perceived risk of recurrence, either weekly subcutaneous injections of idraparinux or standard therapy — heparin followed by an adjusted-dose vitamin K antagonist.

Investigators looked at recurrence of DVT or PE as a measure of efficacy, and clinically relevant bleeding was the main safety outcome. The study, published in The New England Journal of Medicine (2007;357:1094), showed that idraparinux displayed similar efficacy to the standard therapy for patients with DVT, but was less efficacious than standard therapy for patients with PE.

For patients treated for DVT, 2.9 per cent in the idraparinux group had a DVT recurrence by day 92 compared with 3.0 per cent in the standard therapy group (odds ratio 0.98, 95 per cent confidence interval 0.63–1.50).

By day 92, rates of clinically relevant bleeding were lower in the idraparinux group than in controls (4.5 per cent versus 7.0 per cent; P=0.004), but at six months the rates of bleeding were similar between groups.

By day 92, PE patients treated with idraparinux experienced 3.4 per cent recurrence compared with 1.6 per cent for those on standard therapy (2.14, 1.21–3.78).

The authors say: “If the apparent difference in efficacy that we observed in our trials is real, this observation challenges the concept that the same anticoagulant regimen is adequate for both deep venous thrombosis and pulmonary embolism.”

A separate study looked at idraparinux for extended prophylaxis of venous thromboembolism (ibid, p1105). Investigators recruited 1,215 patients who had been treated for six months with idraparinux or a vitamin K antagonist following a confirmed thromboembolic event. They were randomised to receive once weekly idraparinux injections or placebo for a further six months.

Compared with placebo, idraparinux was effective in preventing recurrent venous thromboembolism over the six-month extension period (P=0.002) but was associated with an increased risk of major bleeding (P<0.001), including fatal intracranial haemorrhage. The authors conclude that “the net clinical benefit of such treatment is marginal”.