6 May

Doctrine of equivalents for life science patents in China

Liu Shen & Associates

The doctrine of equivalents is an important principle in patent infringement disputes. It could prevent the accused infringer evading liability for the infringement by making insubstantial changes to a patented alternative. However, determination of an equivalent feature can be tricky.

Legal authority

In 2009 the Supreme Court in China introduced the concept of the ‘doctrine of equivalents’ as another major rule to be considered alongside literal infringement.

In 2016 the criterion for applying the doctrine of equivalents was further clarified as the ‘function-way-result’ test, meaning that the equivalent features should perform substantially the same function in substantially the same way to obtain substantially the same result.

Accordingly, a general routine to determine patent infringement would be to first perform an element-by-element analysis between the accused infringing product or process and the asserted claim. If no literal infringement is concluded, then the doctrine of equivalents should be considered. To be an equivalent technical feature, the alternative feature should pass the function-way-result test.

Function-way-result test

In 2014 the Zhejiang High Court issued a decision in Hangzhou Grascent Co Ltd v Hangzhou Youbang Flavors & Fragrances Co Ltd, setting an example of how to apply the doctrine of equivalents in a patent infringement dispute.

Grascent owned a patent relating to a method of preparing epoxy pinane from pinene with sodium percarbonate, in which acetic anhydride was added into a mixture of pinene and sodium percarbonate. In the asserted claim, the molar ratio between pinene and sodium percarbonate was defined as 1:(1.1-3.0), while in the technical solution carried out by Youbang, the corresponding molar ratio was 1:1.011.

The first-instance court concluded that there was no infringement under the doctrine of equivalents, since the patent at issue specifically defined the molar ratio range, while what was applied by Youbang clearly fell outside it. However, the decision was reversed by Zhejiang High Court.

The second-instance court first clarified the meaning behind the molar ratio feature. One of the issues in dispute in the first instance was whether the “effective oxygen” content of sodium percarbonate should be taken into consideration even if it was not specified in the asserted claim. According to the description of the patent at issue, the role of sodium percarbonate in the method would be to provide effective oxygen for the oxidation of pinene. How much effective oxygen is contained in sodium percarbonate would directly affect the molar ratio between pinene and sodium percarbonate. Although the asserted claim does not define the effective oxygen content, the description recites that, “sodium percarbonate is an inorganic compound … comprising 12-13% of ‘effective oxygen’”. In this regard, the real meaning behind the molar ratio definition would be with the effective oxygen content at 12% to 13%, the molar ratio between pinene and sodium percarbonate should be 1:(1.1-3.0) to provide excessive sodium percarbonate.

After clarifying the meaning of the molar ratio, the next step would be to determine whether the two molar ratios are equivalent. For this, the court performed the function-way-result test.

First, the court opined that the two methods are substantially the same ways to obtain epoxy pinane. Although Youbang selected a slightly different molar ratio, this was simply because their sodium percarbonate comprised more effective oxygen (ie, 13.5%). This would not change the fact that both methods relate to oxidising pinene with excessive sodium percarbonate. With a higher effective oxygen amount in sodium percarbonate, it would be conceivable for skilled artisans to adjust the molar ratio between the two reactants, with no inventive labour involved.

Second, the two methods were determined to have substantially the same function, that is, to apply excessive sodium percarbonate for a complete oxidation of pinene.

With sodium percarbonate being the oxidant, both methods overcome the defects of other peroxy compounds and assure a stable and safe reaction procedure, achieving substantially the same result.

Based on the above analysis, the court concluded that the molar ratio of the accused infringing technical solution should be equivalent to the molar ratio range as defined by the patent at issue.

There are two take-away messages from this case. First, intrinsic evidence is paramount in claim construction. In this case, although the asserted claim does not specifically recite the effective oxygen amount in sodium percarbonate, it was still taken into consideration, since the description indicates that the amount is closely related to the molar ratio feature. Second, to determine whether two features are equivalent, they should be reviewed from three aspects: function, way, result.

Patent infringement practice in biological cases

China usually applies a strict practice on patent applications relating to biological sequences. The claims involving biological sequence are often required to be restricted into specific sequences in prosecution. This would lead to a question of how to apply the doctrine of equivalents during patent infringement litigation. State Serum Institute v Beijing Wantai Biopharmaceutical Co Ltd (2016) provides guidance on how to deal with this issue.

In this case, State Serum Institute accused Wantai Biopharma of infringing its patent pertaining to a diagnostic kit for detecting Mycobacterium tuberculosis infection. Specifically, the asserted claim of the patent at issue reads: ‘A diagnostic kit comprising: (a) Tb38-1 peptide; and (b) a detection reagent’. According to the description, Tb38-1 is a peptide of 95 amino acids. It is an antigen of Mycobacterium tuberculosis and is capable of binding to specific antibodies in the serum of the individual infected.

Wantai Biopharma used CFP-10 peptide as the antigen for detecting Mycobacterium tuberculosis infection. Compared to Tb38-1, 5 residues, MAEMK, were introduced at the N-terminal of CFP-10. The major issue in this case was whether the two peptides are equivalent.

Both the first and second-instance courts upheld Wantai’s claims and opined that there was no substantial difference between CFP-10 and Tb38-1. In terms of the peptide sequence, the five additional residues in CFP-10 include three non-polar amino acids and thus the epitope should not fall into this region. Therefore, the epitopes of both CFP-10 and Tb38-1 fall into the overlapping region of the two peptides. The detection of the Mycobacterium tuberculosis infection depends on the structure of the epitope. Since CFP-10 shared the same epitope with Tb38-1, and both peptides were used for detecting Mycobacterium tuberculosis, they should be equivalent to each other.

Although CFP-10 involves five additional residues at the N-terminal, and is therefore not identical with Tb38-1, Wantai Biopharma failed to prove any functional difference brought by the mutation. Consequently, the courts concluded that there is no substantial difference between the two peptides.

Guangdong High Court’s decision in this case offered an insight into how far a claim involving biological sequences should be extended under the doctrine of equivalents. That is, a substantially different function should be a major consideration. If the accused infringer failed to provide any evidence indicating the different function due to the mutation in the biological sequence (eg, in this case, the different structure of epitope), the two sequences would be held equivalent.

Replacement of components in pharmaceutical formulations

For patent infringement disputes in the field of pharmaceutical formulation, one major issue that is usually in dispute is whether the doctrine of equivalents should be applied when there is a replacement of components between the accused infringing product and the patent at issue. The following two cases give an insight into how this question would be decided.

In Anhui Tuote Biological Engineering Co Ltd v Beijing Zhongsheng Jinyu Diagnostics Technology Co Ltd (2016), Jinyu Diagnostics owned a patent pertaining to a kit for detecting aerobic flora in vaginal secretions. In Claim 1 of this patent, the kit comprised a reactor coated with Gly-Arg-beta-naphthylamine, with the chromogenic reagent being Fast Blue B. As found by the courts, in the presence of coagulase, Gly-Arg-beta-naphthylamine would be cleavaged into Gly-Arg and beta-naphthylamine, the latter then participates in the colouring process by reacting with the chromogenic reagent.

The corresponding coating compound in the accused infringing kit produced by Tuote Biological is Gly-Arg-4-methoxy-beta-naphthylamine, with the same chromogenic reagent Fast Blue B. Gly-Arg-4-methoxy-beta-naphthylamine would be hydrolysed under the action of coagulase, generating Gly-Arg and 4-methoxy-beta-naphthylamine. Then, the beta-naphthylamine moiety reacts with Fast Blue B for colouring.

The first and second-instance courts both held that Gly-Arg-beta-naphthylamine and Gly-Arg-4-methoxy-beta-naphthylamine were equivalent, because it is beta-naphthylamine which is involved in the colouring reaction and that the 4-methoxy substituent plays no role in such process. With or without the methoxy group, there would be no substantial difference in terms of the colouring mechanism. Moreover, there is no obvious difference in terms of the detecting efficacy. Although Tuote Biological claimed that the introduction of 4-methoxy could enhance the affinity and sensitivity, it failed to provide any evidence.

In an earlier case, Hubei Wushi Pharmaceutical Co Ltd v Aonuo Pharmaceuticals (2009) provided an example in which the doctrine of equivalents was not applied. The asserted claim related to an oral solution comprising glutamine or glutamic acid, while the accused infringing product comprised lysine HCl. One of the issues in dispute was whether lysine HCl should be equivalent with glutamine/glutamic acid.

During the trials, Wushi Pharm cited another patent of Aonuo (Patent ‘587) as evidence to prove the non-equivalence between the two substances, which later became an important basis for the Supreme Court to reverse the Hebei High Court decision.

Patent ‘587 relates to an oral solution, which also differs from the patent at issue in glutamine/glutamic acid versus lysine HCl. During the prosecution of ‘587, the patentee stated that, compared with glutamine/glutamic acid, the addition of lysine HCl significantly improved the solubility and stability of calcium gluconate, with experimental data to demonstrate this.

Based on the above facts, the Supreme Court held that there is a substantial difference between lysine HCl and glutamine/glutamic acid. The two substances are therefore not equivalent.

From the above comparison, the difference in terms of technical effect is a major consideration in determining whether the replacement of substances is equivalent. Should Tuote Biological have provided evidence to demonstrate the enhanced affinity and sensitivity brought by 4-methoxy, instead of a simple statement, a different result would have been achieved.

Limitation on doctrine of equivalents

Although the doctrine of equivalents is an important legal method to determine infringement in cases of non-literal infringement, the expanded coverage permitted by this doctrine is not unbounded. An unlimited application of the doctrine of equivalents would weaken the notice of a patent claim, harming the public interest.

One important limitation that is put onto the doctrine of equivalents is prosecution history estoppel, which prevents the patentee from using equivalence to recapture coverage that was surrendered during prosecution or an invalidation procedure.

Tuote Biological v Jinyu Diagnostics and Wushi Pharm v Aonuo Pharm also provide an interesting comparison in applying estoppel.

In Wushi Pharm v Aonuo Pharm another issue in dispute was whether the calcium gluconate in the accused infringing product was equivalent to the active calcium as defined in the asserted claim. The court concluded that the two features were not equivalent by taking estoppel into consideration.

Specifically, the active calcium in the asserted claim was amended from the soluble calcium to overcome the non-support issue in prosecution. In this regard, the court held that the patentee surrendered other soluble calcium except active calcium. According to the description of the patent at issue, both calcium gluconate and active calcium are specific examples of soluble calcium. Therefore, the patentee was not allowed to recapture the surrendered calcium gluconate into coverage.

Similarly, in Tuote Biological v Jinyu Diagnostics, Jinyu Diagnostics restricted the reactor in prosecution by defining it is coated with Gly-Arg-beta-naphthylamine. However, no estoppel was applied to such limitation. Since the granted Claim 1 was actually obtained from the original Claim 3, the court opined that no specific technical solution was surrendered. Therefore, the prosecution history estoppel was not applied in this case.

In Tuote Biological, Zhejiang High Court clarified the meaning of ‘surrendered technical solutions’, which refers to those that were surrendered due to the amendment or observations made by the applicant/patentee for the reason of patentability. In this case, taking the original Claim 3 alone, no limitation was made to Gly-Arg-beta-naphthylamine itself, nor did the patentee expressly disclaim any specific technical solution in prosecution. Therefore, no estoppel should be applied.

Through the comparison of the two cases, to avoid triggering the potential estoppel, the patentee should pay attention to the claim amendment and observation in prosecution and try not to expressly disclaim any specific technical solutions. Drafting the claims in a multi-layer format could also be helpful, which would allow the patentee to choose the dependent claim for amendment, without surrendering any coverage.

Another limitation on the doctrine of equivalents is the doctrine of dedication, which was also introduced in China in 2009 by the judicial interpretation of the Supreme Court, meaning a subject matter disclosed in the specification but not claimed by the patentee would be considered as a dedication to the public and cannot be recaptured. The consideration behind this interpretation is that the applicant would claim a narrower scope out of a broad coverage in the description, and later in an infringement litigation assert the expanded portion in the description being an equivalent feature, thus unduly expanding the extent of protection. The introduction of the dedication doctrine would prevent such circumstances and balance the interests between the patentee and the public.

Implications on patent practice

One of the major highlights in the latest round of judicial reforms is the establishment of China’s case guidance system, recognising case law as an important supplement to judicial interpretation, with the IP courts taking the lead.

Looking at the Supreme Court and High Court decisions, the function-way-result test appears to be crucial for determining equivalence. An equivalent technical feature would be determined only when it has passed all three aspects of the test.

For a patentee to avoid precluding the doctrine of equivalents, attention should be paid to amendment and observations in prosecution and invalidation procedure. That is, try to avoid any unnecessary amendments or statements that could objectively establish a surrender of subject matters. Multiple dependent claims are recommended for patent drafting, since they would back up amendments and reduce the risk of disclaimers. Moreover, careful management of relevant cases is important. One lesson that could be learned from Wushi Pharm v Aonuo Pharm is to try to avoid a prosecution history that could potentially affect the enforcement of another patent held by the patentee.

Liu Shen & Associates

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Yuan Zhang

Patent attorney

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Yuan Zhang is a patent attorney at Liu Shen & Associates. She specialises in IP issues related to patents, including patent drafting, prosecution, reexamination and invalidation, as well as non-litigation services such as validity opinions and free-to-operate analysis. She has expertise in the pharmaceutical, chemistry and biology fields. Dr Zhang joined Liu Shen & Associates in 2015 and qualified as a patent attorney in the same year. She received her BSc in chemistry (2006) from Nankai University (China), and her PhD in chemistry (2011) from Iowa State University (United States).

Zongliang (Stephen) Zou


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Zongliang (Stephen) Zou is a partner at Liu, Shen & Associates. He assists clients in matters involving all types of IP right, focusing on patent prosecution and patent administrative and judicial litigation. Dr Zou is experienced in preparing patent infringement, validity and freedom-to-operate opinions and counsels clients in various matters relating to IP rights and drug regulatory matters.

Dr Zou started his IP career with Liu, Shen & Associates in 2003. Before this, he was involved in pharmaceutical research. Dr Zou obtained a PhD in pharmaceutical chemistry from the Chinese Academy of Military Medical Science and obtained an LLM in IP law from John Marshall Law School.