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2026-03
One Case a Day | China: Closest Prior Art Should First Consider the Same or Similar Technical Field - Reexamination Decision No. 100159 (2015)
Case Introduction
Determining the closest prior art is the starting point for correctly assessing inventive step and is also one of the most easily overlooked aspects in Chinese patent practice. The closest prior art can be one of two types of existing technologies:
① Same technical field + closest technical problem, technical effect, or intended use ± discloses the most technical features;
② Different technical field, but capable of achieving the function of the invention and discloses the most technical features.
From the above, it can be seen that the same technical field is the most important requirement for the closest prior art. In EPO practice, almost only type ① disclosures are accepted as the closest prior art. Only the person skilled in the art based on such prior art, facing the relevant technical problem and striving to reconstruct the R&D process, can evaluate inventive step as objectively as possible.
Case Information
Application Number: 201110393196.1
Title of Invention: Polyethylene Glycol-Tamsulosin Conjugate and Pharmaceutical Composition Thereof
Applicant: Tianjin Keyan Technology Co., Ltd.
Application Date: December 1, 2011
Decision Number: No. 100159
Decision Date: October 28, 2015
Key Points of the Decision
The closest prior art refers to the single technical solution among the existing technologies that is most closely related to the claimed invention. It can be: existing technology in the same technical field as the claimed invention, with the closest technical problem to be solved, technical effect, or intended use, and/or disclosing the most technical features of the invention; or, existing technology in a different technical field from the claimed invention, but capable of achieving the function of the invention and disclosing the most technical features of the invention. When determining the closest prior art, priority should be given to existing technologies in the same or similar technical fields.
Key Stages of the Case
The involved application's claim 1 seeks protection for a polyethylene glycol-tamsulosin conjugate. According to the description, this patent uses PEGylation technology to structurally modify tamsulosin, linking low molecular weight polyethylene glycol with tamsulosin to increase the water solubility of tamsulosin itself, thereby reducing its toxic side effects on the central nervous system.
Comparative Document 1 ("PEG-modified Penicillin Acylase and Its Partition in Aqueous Two-Phase Biotransformation Systems," publication date February 28, 2001) aims to form an aqueous two-phase biotransformation system (biotransformation based on the partition difference of enzymes and products in a two-phase system, enriching the enzyme in one phase while most products of the enzyme-catalyzed reaction actively transfer to the other phase). The technical means employed is chemical modification of penicillin acylase with PEG. The final effect achieved is that in an equilibrium system where the upper phase is rich in PEG and the lower phase is rich in dextran, the modified enzyme is almost completely partitioned into the PEG phase, creating favorable conditions for aqueous two-phase biocatalysis. Comparative Document 1 focuses on the influence of reaction conditions on enzyme activity and the partition problem of PEG-modified enzymes in aqueous two-phase systems.
When determining the closest prior art, priority should be given to the same or similar technical fields. The technical field of Comparative Document 1 is clearly different from that of this application. The tamsulosin described in this application is a drug for treating benign prostatic hyperplasia, belonging to the field of urological disease therapeutic drugs. As stated in the description of this application, the invention relates to the field of therapeutic drugs for benign prostatic hyperplasia. The active ingredient tamsulosin used is a known drug for treating benign prostatic hyperplasia in the prior art, and there have been many studies on PEG modification of small molecule drugs in the prior art (background section of the description). In contrast, the penicillin acylase described in Comparative Document 1 is mainly used in the preparation of semi-synthetic antibiotics and their intermediates, belonging to the chemical engineering field.
The technical problems to be solved, technical effects, or intended uses are also different. Comparative Document 1 aims to form an aqueous two-phase biotransformation system to facilitate catalytic reactions, while this application aims to reduce the toxic side effects of tamsulosin on the central nervous system.
Furthermore, Comparative Document 1 cannot achieve the function of this invention.
In terms of shared technical features, Comparative Document 1 and this application share only one identical technical feature, namely polyethylene glycol (PEG). However, there is a significant difference in molecular weight. The PEG molecular weight in claim 1 of this application is 282, while in Comparative Document 1 it is 10,000. Different molecular weights determine different properties and applications of PEG, leading to obvious distinctions in their physical and chemical impacts on the modified substance.
According to the provisions of the Examination Guidelines regarding "Determining the Closest Prior Art," Comparative Document 1, which belongs to a different and dissimilar technical field from this invention, solves different technical problems, achieves different technical effects, functions, or uses, and shares only one identical technical feature, cannot possibly constitute the closest prior art.
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