Synthon BV v Smithkline Beecham plc (House of Lords)

08 December 2005

Adrian Howes


The House of Lords on Thursday unanimously allowed Synthon BV’s (“Synthon”) appeal for the revocation of Smithkline Beecham plc’s (“SB”) patent for the methane sulfonate salt of paroxetine. Heavily criticising the Court of Appeal’s judgment, Lord Hoffman, giving the principal statement, found that on considering the concept of enabling disclosure in a patent specification a clear distinction should be made between the “disclosure” element and the “enablement” requirement. He further highlighted the fact that although for the purposes of assessing disclosure “the prior inventor must be clearly shown to have planted his flag at the precise destination before the patentee”[1] on considering “enablement”, particularly in cases concerning complex technology, one should have regard to what an ordinary skilled man in the art might consider trying in attempting to replicate the disclosed material.


On 7 March 2001 Synthon commenced proceedings to have SB’s patent for crystalline paroxetine methansulfonate (“PMS”) revoked on the ground that it was invalid for lack of novelty, relying on their own earlier patent application and section 2(3) of the Patents Act 1977.

Section 2(3) provides that, for the purposes of novelty only, the state of the art may include “matter contained in an application for another patent which was published on or after the priority date of that invention, if … (a) that matter was contained in the application for that other patent both as filed and as published; and (b) the priority date of that matter is earlier than that of the invention”.

PMS is a salt of paroxetine, a drug that has been commonly used, in its hydrochloride hemihydrate salt form, to treat depression and known commonly as Seroxat and Paxil. PMS has properties making it more suitable for pharmaceutical use than the hydrochloride hemihydrate form as it is more stable, less hygroscopic and much more soluble.

On 10 June 1997 Synthon filed an international application for a patent claiming a broad class of sulfonic acid salts including PMS, which was specifically mentioned by way of an example. The application was published on 17 December 1998.

On 6 October 1998 SB filed a document in the UK, giving it that priority date, and later filed a patent application on 23 April 1999 for PMS based on that priority filing. It was the validity of this patent that was in issue in the case.

The case went before Jacob J who on the 3 December 2002 revoked the patent. Jacob J concluded that Synthon’s patent disclosed the existence of PMS in the crystalline form specified in SB’s patent, that crystalline PMS was monomorphic (having only one possible crystalline form) and that the ordinary skilled man in the art would be able to reproduce crystalline PMS as claimed in SB’s patent.

SB appealed the decision.

Court of Appeal decision

On 25 June 2003 the Court of Appeal overturned Jacob J’s decision, Aldous LJ distinguishing Synthon’s and SB’s disclosures: “the [SB patent] is directed at PMS, whereas the [Synthon application] is directed at a large number of compounds both in the general statements and in the preferred form. Second, the general statements as to how PMS can be obtained differ from those relating to the compounds in the application. Third, the examples in the patent give detailed instructions as to how crystalline PMS can be made, whereas the equivalent example in the application does not work. Fourth, the patent claims a different crystalline form of PMS to that described in the application”.[2]

On considering the expert evidence Aldous LJ added that “the crucial question was not whether the skilled addressee would expect success, but whether the application made available PMS as claimed … Once it had been established that [the PMS example in the Synthon application] did not disclose a successful route to PMS as claimed in the patent, the skilled addressee might have adopted obvious modifications. But such an approach is not permissible when considering novelty” concluding that “the disclosure in the application does not make the PMS claimed … available to the public”.[3]

The case was then referred by Synthon to the House of Lords.

House of Lords judgment

The House of Lords unanimously overturned the Court of Appeal’s verdict and revoked SB’s patent. Lord Hoffman, giving the main judgment, heavily criticised the Court of Appeal’s judgment.

Lord Hoffman’s principal criticism was of Aldous LJ’s lack of clarity and distinction between the two requirements for anticipation “prior disclosure” and “enablement”. Making clear that the two concepts should be considered separately, he briefly analysed the relevant case law noting that although for the purposes of disclosure “the matter relied upon as prior art must disclose subject-matter which, if performed, would necessarily result in an infringement of the patent”[4] this does not hold when considering enablement. “Enablement means that the ordinary skilled person would have been able to perform the invention which satisfies the requirement of disclosure”[5]. The “person skilled in the art is assumed to be willing to make trial and error experiments to get it to work.”[6] Therefore “once the meanings of the prior disclosure and the patent have been determined, the disclosure is either of an invention which, if performed, would infringe the patent, or it is not. The person skilled in the art has no further part to play. For the purpose of enablement, however, the question is no longer what the skilled person would think the disclosure meant but whether he would be able to work the invention which the court has held it to disclose”.[7]

Lord Hoffman also added that he could see no reason why there should be any difference between the test of enablement for the purposes of prior disclosure and that for the purpose of sufficiency under section 72 of the Patents Act 1977.

In applying the facts of the case Lord Hoffman had no doubt that Synthon’s application disclosed the existence of PMS crystals even though Synthon had mistakenly included an IR spectrum differing from that indicated in SB’s patent, suggesting PMS to be polymorphic (having more than one crystalline form). However, a variety of experiments conducted prior to the trial suggested that PMS was monomorphic. This being the case Lord Hoffman considered that the Judge at first instance had been right to disregard the IR spectrum and conclude that the PMS monomorph had been disclosed by Synthon’s application. In that “the subject-matter described was crystalline PMS and a skilled person who performed that invention, though he might, if he had read the patent, think that he was not going to infringe it, would inevitably do so.”[8] Whether the crystals could be made or not was a question of enablement.

For enablement the issue becomes whether in fact the ordinary skilled man in the art would have been able to make crystalline PMS. Synthon had in their example unfortunately named a solvent that was unsuitable for crystallisation. In the trial Judge’s opinion a skilled man would have tried a different solvent, either from the range mentioned in the application or forming part of his common general knowledge. Lord Hoffman could see no reason why this opinion of fact should be interfered with.

On considering Aldous LJ’s four points on the two disclosures, above, Lord Hoffman believed the first and fourth to be irrelevant. The idea of making crystalline PMS was clearly disclosed in the application and PMS is in fact monomorphic. The second and third points were relevant to enablement and not disclosure. Lord Hoffman further criticised Aldous LJ’s conclusion on the expert evidence, above, for disregarding the Jacob J’s opinion that a skilled addressee would have considered “obvious modifications”.

First published in the November 2005 issue of WIPR.

[1] General Tire and Rubber co v. Firestone Tyre and rubber Co Ltd [1972] RPC 457

[2] Synthon BV v. Smithkline Beecham plc [2003] EWCA Civ 861, para. 52

[3] ante. para. 56

[4] Synthon BV v. Smithkline Beecham plc [2005] UKHL 59, para. 22

[5] ante, para. 26

[6] ante, para. 30

[7] ante, para. 32

[8] ante, para. 37