Germany’s Boehringer Ingelheim has moved to block a patent challenge in the USA to its anti-platelet agent Aggrenox by Barr Laboratories.

The news comes as Barr said that it has received notice from the US Food and Drug Administration that its Abbreviated New Drug Application to make generic Aggrenox (aspirin/extended-release dipyridamole) has been accepted for filing, making it the first firm to seek approval to market a copycat version of the treatment. If successful, Barr would be entitled to six months' market exclusivity.

However, Boehringer has filed suit in the US District Court in Delaware in an attempt to stop Barr's bid to copy the drug which is indicated to reduce the risk of stroke in patients who have had transient ischemia of the brain or completed ischemic stroke due to thrombosis. The product had US sales of around $258 million for the twelve months ended May 2007, according to Barr.

Aggrenox is a key product for Boehringer and is at the heart of the firm’s PRoFESS trial, which is the world’s largest secondary stroke prevention study and has enrolled over 20,000 patients in 35 countries. Its aim is to demonstrate that Aggrenox is superior in preventing secondary strokes compared with Plavix (clopidogrel), the antithrombotic blockbuster sold by Bristol-Myers Squibb and Sanofi-Aventis, and the results are schedule to be presented next May.

Impressive dabigatran data presented

Speaking of antithrombotics, Boehringer has presented strong Phase III data for its once-daily oral direct thrombin inhibitor Rendix (dabigatran) which show that the drug is effective and safe in preventing venous thromboembolism after orthopaedic surgery.

The company presented data from the 3,494-patient RE-NOVATE trial at the XXI Congress of the International Society on Thrombosis and Haemostasis in Geneva, Switzerland, which demonstrated that Rendix, administered for an average of 33 days, was as effective as injections of the standard treatment, Sanofi’s Lovenox (enoxaparin), in VTE and all-cause mortality after total hip replacement surgery. Also there was a low rate of bleeding associated with dabigatran, with major bleeding rates comparable to Lovenox.

Boehringer said that current guidelines recommend that patients undergoing hip replacement surgery receive extended thromboprophylaxis with low molecular weight heparins such as Lovenox or vitamin K antagonists like warfarin for up to 28 to 35 days following surgery, but current hospital stays can be less than five days. Although effective, “both LMWHs and VKAs have drawbacks which can limit their use, especially outside the hospital setting”, the firm noted and unlike enoxaparin, which is only available as a subcutaneous injection, dabigatran is given as a capsule “from early in the postoperative period, and does not require the frequent coagulation monitoring and dose adjustment of warfarin”.

Rendix has already been filed in Europe for the prevention of deep-vein thrombosis in conjunction with hip or knee joint replacements. The compound is currently being evaluated in a number of thromboembolic disease indications in a global clinical trial programme entitled RE-VOLUTION. It is expected to involve more than 27,000 patients from Asia, Australia, Europe, the Americas, and South Africa.