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May And Baker Ltd & Ors v. Boots Pure Drug Company Ltd
Factual and Procedural Background
Letters Patent No. 533,495 for certain “sulpha” drugs were granted on 24 May 1946 to the joint patentees—“Company A” (an English corporation) and “Company B” (a Swiss corporation). In September 1946 the Respondent, “Company C,” petitioned for revocation of the patent. The patentees then moved for leave to amend the specification so as to confine the patent to two specific compounds (sulphathiazole and sulphamethylthiazole). The motions were heard together by Judge Jenkins, who:
- Revoked the patent; and
- Refused leave to amend.
The Court of Appeal unanimously affirmed, addressing only the refusal to amend. The patentees appealed to the House of Lords. They conceded that, absent leave to amend, the revocation must stand. The appeal therefore turned exclusively on whether the proposed amendment should have been allowed.
Legal Issues Presented
- Does the proposed amendment violate the proviso to section 22 of the Patents and Designs Acts 1907-1946 by causing the specification, as amended, to “claim an invention substantially larger than, or substantially different from,” that originally claimed?
- (Ancillary) If competent, should the court exercise its discretion to allow the amendment?
Arguments of the Parties
Appellants’ Arguments
- The amendment is a permissible disclaimer; it merely narrows the claim to the only embodiments specifically described, therefore it cannot amount to a “substantially different” invention.
- Section 22 is intended to let patentees cure over-broad claims; prohibiting the amendment would defeat that policy and penalise empirical chemical research.
- Precedent (e.g., Seed v. Higgins) shows that a patentee may abandon general claims and retain a specific embodiment already disclosed.
Respondent’s Arguments
- The original specification asserted a monopoly over an immense class—millions—of benzene-sulphonamido-thiazole derivatives, said to possess therapeutic value.
- Replacing that broad genus with a claim to only two compounds shifts “the centre of gravity” of the patent; the inventions are fundamentally different and section 22 forbids such an amendment.
- The patentees are attempting to secure protection for discoveries made after filing, contrary to patent policy.
Table of Precedents Cited
| Precedent | Rule or Principle Cited For | Application by the Court |
|---|---|---|
| Seed v. Higgins (1856) | Disclaimers may lop off “vicious excess” while leaving a perfect description intact. | Distinguished: Unlike Seed, the present amendment would leave no part of the original generic invention intact. |
| Ralston v. Smith (1863) | A disclaimer cannot convert “a barren and unprofitable generality” into a valid specific claim. | Relied on to show that wholesale abandonment of the original invention is impermissible. |
| Wistoft’s Application (1929) | Amendment is barred if it introduces a new idea or shifts the invention’s “centre of gravity.” | Used to support the view that limiting millions of compounds to two shifts the invention’s centre of gravity. |
| British Thomson-Houston (1919) | Removing matter can be impermissible if coupled with an increased specification of what remains. | Cited by analogy: the proposed specification would import a new focus on two compounds. |
| Johnson’s Patent (1937) | Section 22 permits narrowing amendments, but not if they create a substantially different invention. | Quoted for the ordinary meaning of “substantially different.” |
| Raleigh Cycle [House of Lords 1950] | Legitimacy of “preferred embodiment” claims. | Cited by Appellants; majority held case did not justify the present amendment. |
Court’s Reasoning and Analysis
Delivering the leading speech, Judge Simonds analysed the original specification in detail:
- The consistory clause, title, and claims together asserted that all benzene-sulphonamido-thiazole derivatives had therapeutic value.
- The only two compounds actually exemplified (sulphathiazole and sulphamethylthiazole) were presented merely as illustrations of that broad invention.
- Under section 22 the Court must compare the invention claimed before and after amendment, not simply the ambit of monopoly. The proposed amendment would transform a vast, generic invention—covering “a fragment of organic chemistry so numerous that the number becomes meaningless”—into two specific drugs with unique characteristics.
- Such a transformation is “plain common sense” evidence of a substantially different invention; the patentee is “shifting the centre of gravity … from the centre of the circle to the very edge of the circumference.”
- Precedents permitting disclaimers (e.g., Seed v. Higgins) involve lopping off severable excess matter; here the entire original invention is abandoned.
- The minority view (Lords Morton and Reid) that the two compounds were the “preferred embodiment” already disclosed was rejected: the absence of any separate claim to those compounds in 1939 indicated the patentees never regarded them as a distinct invention.
Holding and Implications
APPEAL DISMISSED. The House of Lords (majority) affirmed the Court of Appeal and refused leave to amend. Because the patentees had conceded that revocation must follow if amendment were refused, the patent stands revoked.
Implications: The decision underscores the strict limits on post-grant amendment under section 22. A patentee may not rescue an over-broad pharmaceutical patent by disclaiming nearly all of the originally claimed genus; doing so is deemed to create a “substantially different” invention. The ruling provides authoritative guidance on empirical drug patents and narrows the scope for remedial amendments in United Kingdom patent practice.
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