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China Patent Office upholds the validity of the blockbuster antiallergic drug patent

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The China Patent Office upheld the validity of the patent over the antihistamine desloratadine citrate disodium, as Yue Guan from Wanhuida Intellectual Property explains

The China Patent Office rendered a decision #50420 in favour of the patentee in a patent invalidity proceeding on June 25 2021. This decision upheld the validity of the compound patent concerning the second-generation antihistamine medication desloratadine citrate disodium. The petitioner did not institute an administrative proceeding and the decision has come into effect.

The contested patent ZL02128998.0 (‘the patent’), which is entitled “alkali-metal or alkali-earth metal complex salt of delotadine polyprotic acid and the medical composition thereof”, protects the marketed drug desloratadine citrate disodium (‘the complex salt’) that holds a significant share of the Chinese market in second-generation antihistamine medication.

The feud originated from a partnership which went sour. The petitioner’s parent company and another subsidiary corporation thereof brought China's first active pharmaceutical ingredient (API) anti-monopoly lawsuit against the patentee. The patentee then found that the petitioner, its parent company, and the said subsidiary were collectively engaged in manufacturing, selling, and using desloratadine product without securing a license from the patentee.

The patentee therefore initiated a patent infringement proceeding against these entities before the court, seeking damages of over RMB 90 million ($14 million). As a counter-measure, the petitioner filed an invalidity action against the patent before the China National Intellectual Property Administration (CNIPA) in October 2020.

The petitioner submitted a substantial amount of evidence in the invalidity procedure, including notarised experimental records, to prove that the patent at issue was not sufficiently disclosed and was devoid of inventiveness.

Arguments of the petitioner and the patentee

The petitioner contended that:

  • The description of the patent at issue failed to incorporate the spectrogram data that could be leveraged by the person skilled in the art to ascertain the chemical structure of the complex salt prepared in the embodiment;

  • The experimental evidence showed that the complex salt cannot be prepared through the documented method, and the data on the effect of compatible stability of the complex salt and excipients mentioned in the description was devoid of authenticity. Therefore, the patent at issue did not sufficiently disclose the preparation method and the technical effects of the complex salt.

    In addition, even if the effects documented in the description were to be considered, given that the patent at issue did not specifically confirm the crystal or other forms of the complex salt, it could not be deduced that the technical effects were achieved by the complex salt per se rather than the crystal form thereof.

    Therefore, the disclosure of the description was insufficient and the inauthentic data surrounding the compatible stability should not be admitted in supporting the inventiveness of the patent.

The patentee conducted a point-by-point rebuttal of the allegation as follows:

  • Although the petitioner cited notarised experimental evidence, to which the petitioner attempts to lend credence by the notarisation process, the evidence was fundamentally flawed with respect to experimenters, key raw materials, preparations, and tests, which crippled its authenticity;

  • The description documents the preparation method for the complex salt and determined the melting point. It further characterises its water solubility and the compatible stability with excipients. Therefore, the patent at issue sufficiently discloses the claimed complex salt, which already meets the examination criteria on sufficient disclosure.

CNIPA made a detailed analysis of the petitioner's evidence and arguments, and its decision shed some light on several hot-button issues in the granting and affirmation of patent rights. This included the questions of parameters in assessing the authenticity of experimental evidence and the sufficient disclosure of compound inventions.

Regarding the authenticity of the experimental evidence, CNIPA found the patentee’s argument tenable, affirming that the experimental evidence had major defects. CNIPA noted that the experimenters are stakeholders of the petitioner, that the process of sending samples to test was not notarised, and that the key reaction materials were not confirmed.

CNIPA concluded that the notarised experimental evidence was inadmissible and that the patent at issue met the requirements of sufficient disclosure.

The China Patent Office also wrote on the examination criteria for the sufficient disclosure of compound inventions. According to the Office, compound inventions protect substances with specific chemical structures, and structural confirmation data such as spectrogram are not essential in patent drafting, as long as a skilled person could affirm that the compound could be obtained through the preparation method documented in the description. In addition, compound invention does not involve the crystal or other solid forms, which is therefore irrelevant to the matter of sufficient disclosure.

This invalidity decision could serve as a point of reference when it comes to drafting compound patents, the examination criteria for sufficient disclosure, and the formality examination over the authenticity of experimental evidence in invalidity procedures.


Yue Guan


Wanhuida Intellectual Property

T: 86 10 6892 1000


Yue Guan is an associate at Wanhuida Intellectual Property. His areas of technical expertise are chemistry, pharmaceutical and mechanics, and he advises clients on patent drafting, examination, re-examination, invalidity, as well as administrative and civil litigations.

Some of Yue’s recent work includes providing FTO legal opinion for a domestic materials magnate and providing patent validity analysis for a foreign materials giant. He also represented a domestic pharmaceutical conglomerate in prevailing in an invalidity proceeding and the ensuing administrative litigation against a competitor.

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