German pharmaceutical firm Bayer has lost a UK Court of Appeal hearing against a decision to revoke its patent covering its best-selling blood thinner drug Xarelto, helping to clear the way for generic versions of the drug to enter the market.

The dosage patent (European patent (UK) No. 1 845 961) covers the use of rivaroxaban, under the brand name Xarelto and covers its use to prevent blood clots by means of once daily administration.

Bayer was appealing the High Court decision by His Honour Judge Hacon from 12 April which revoked the patent for lacking an inventive step.

The action was brought by a group of generic manufacturers including Sandoz and Teva, who all wish to market generic versions of rivaroxaban. According to research firm Statista, the Xarelto drug generated nearly $4.1bn in revenue in 2023 and is the fourth best-selling drug in the world.

The patent is subject to parallel multi-jurisdictional proceedings with France and South Africa having joined the UK in finding the patent invalid. Bayer has, however, enjoyed more success elsewhere, including Germany, Sweden and the Netherlands.

If the patent had been found valid it would have prevented the generic manufacturers from supplying generic rivaroxaban for once daily administration, although it does not prevent them from supplying it for twice (or more frequent) daily administration.

The generic rivals mainly relied on two pieces of prior art in the form of research posters presented at scientific meetings: one known as the Harder poster and two known as the Kubitza posters.

Lord Justice Arnold delivered the judgment on 24 May, and was joined by Lord Justice Falk and Lady Justice Nicola Davies. Arnold concluded that Hacon made “no error of principle in his assessment of obviousness. His conclusion was grounded in the expert evidence”.

He added that the Harder poster expressly suggests that rivaroxaban is suitable for once daily administration. Harder and the Kubitza posters contain some data to support that statement, at least in the case of a 30 mg dose.

It was therefore “obvious to try including a once daily regimen in the Phase II trial, and the skilled team would have had a reasonable expectation that a 30 mg once daily dose would be efficacious and safe”.

Rivaroxaban itself, and its use for the treatment of thromboembolic disorders, were protected first by European Patent No. 1 261 606, which expired in 2020 and then by a supplementary protection certificate which expired on 1 April 2024.

The hearing of the appeal was expedited because Bayer had been granted a short-term interim injunction to restrain a number of the respondents from marketing rivaroxaban for once daily administration until judgment was given.

Bayer wished that to continue but Arnold said “the flurry of applications for interim injunctive relief was not a sensible use of the resources either of the parties or of the courts”. He also berated the respondents for not bringing the proceedings earlier and for not telling the patents court the significance of the 1 April date.

Bayer was represented by 11 South Square’s Iain Purvis KC and Three New Square’s Miles Copeland and Alice Hart (instructed by A&O Shearman).

The generic manufacturers were represented by 8 New Square’s Adrian Speck KC and Henry Ward and 11 South Square’s Adam Gamsa (instructed by Pinsent Masons, Bristows, HGF Law and Taylor Wessing).