By Geoffrey K. Cooper, Ph.D.  Email
Registered Patent Attorney


            The People’s Republic of China has been criticized in the past for disregarding intellectual property rights, particularly those of foreign corporations.  When China pressed to join the World Trade Organization (WTO) and was finally admitted in 2001, the country became obligated to observe the provisions of TRIPS, the international treaty governing trade-related aspects of intellectual property, as well as other norms of international law.  Subsequently, China’s performance in upholding patent law standards generally agreed upon within the international community has been watched by practitioners of intellectual property law, among others.

            A noteworthy event on this front during the past year was the invalidation by China of Pfizer’s patent CN1124926 concerning the use of sildenafil (Viagra®) for treatment of male erectile dysfunction (ED).  The events leading up to the invalidation of the patent were initiated by requests for re-examination filed by Chinese domestic manufacturers of medicinal compounds including sildenafil.  The invalidated patent in question is the China national phase patent resulting from a Patent Cooperation Treaty (PCT) application filed by Pfizer in 1994.  A brief summary of what is publicly known at present concerning the legal basis for this invalidation, and an analysis of the invalidation of corresponding sildenafil use patents in other countries such as the United Kingdom (UK), is provided herein. 

            It remains to be seen whether the initial rationale given by the Patent Reexamination Board of the State Intellectual Property Office (SIPO) of the People’s Republic of China will be affirmed by the Chinese courts that will judicially review their action, or whether new grounds of invalidation more consistent with the grounds used by the other invalidating countries will ultimately be applied by Chinese courts.  An additional issue is how SIPO and the Chinese courts will treat patent number CN1057464, an earlier Chinese patent also claiming sildenafil.  The perception among the global legal and business communities of the legitimacy of this action will likely influence the tenor of the relationship between these communities and the People’s Republic of China in coming years.

Scientific and Legal Background

            Sildenafil was originally synthesized by Pfizer chemists as part of a large series of related chemical compounds.  It was eventually given the brand name Viagra®.  Sildenafil belongs to the heterocyclic chemical class of pyrazolopyrimidinones, and was found to act as an enzyme inhibitor in mammals, selectively inhibiting cyclic-guanosine-3’,5’-monophosphate (c-GMP) phosphodiesterase (PDE) without causing significant inhibition of cyclic-adenosine-3’,5’-monophosphate (c-AMP) phosphodiesterase.  The inhibition by the drug of one specific member of this class of enzyme, type V (or type 5) c-GMP phosphodiesterase, results in a biochemical and physiological cascade involving nitric oxide (NO) and c-GMP which yields an enhanced capacity in men for an erection to occur under sexual stimulation.  The mechanism of this physiological action is now quite well understood [n1].

            However, this long-sought physiological consequence was not immediately discovered by the creators of the molecule at Pfizer.  The therapeutic uses for which sildenafil and its analogs were originally indicated did not include treatment of ED.  Rather, the medicinal uses originally claimed for the molecular class including sildenafil were in the treatment of angina, hypertension, heart failure and atherosclerosis.  Patent applications filed in the European Patent Office [n2] and the U.S. Patent Office [n3] by Pfizer disclosed and claimed sildenafil along with other compounds as novel compositions of matter, and further disclosed and claimed the use of these compounds in treatment of various cardiac or circulatory disorders, but not ED. 

            Apparently, no PCT application was filed claiming the composition of matter of sildenafil, or an antianginal use specifically for the compound sildenafil [n4], so there is no national phase patent in China derived from a PCT application for the sildenafil composition of matter.  Although two PCT applications for use of closely related pyrazolopyrimidinones in treatment of angina were filed [n5], neither of these discloses or claims the exact molecule sildenafil.

            However, at the time the application for EP0463756 claiming sildenafil as a novel composition of matter was filed, numerous parallel national applications were filed by Pfizer without reliance on the PCT, which were eventually granted in non-EC countries including Australia, Brazil, Canada, China, Japan, Russia and South Africa, among others [n6].  Among these, China Patent CN1057464 was granted by the SIPO on 7 June 1995.

            It should be noted that the grant of the patent by the SIPO took place after China had modified its patent law in 1992 (effective 1 Jan. 1993) to allow claims directed to pharmaceutical compositions of matter and products of chemical processes [n7a].  However, the Chinese national application was filed under the terms of the older version of the patent law of 1985, which did not provide for composition of matter claims.  The fact that the patent issued after the 1992 change suggests that the coverage of the patent claims might well be evaluated under the revised law which does allow for claims to pharmaceutical molecular entities, but this point is unclear.  An additional unknown is the effect that TRIPS might have on the interpretation of this patent.  

            CN1057464 does disclose the exact structure of sildenafil, as shown in Example 12.  Claim 1 is directed to “a method to make the compound showed below and its salts used for medical purposes” and displays a chemical structural class identical to the structural class claimed in claim 1 of EP0463756 [n7b].  The five dependent claims are directed to increasingly more restricted subsets of the class claimed in claim 1.

            It is unknown how Chinese courts might be expected to construe this patent, especially given the changes that have occurred in Chinese patent law over the past 14 years with the two amendments to the law that have come into force during that time.  Under the requirements of TRIPS, Article 27 [n24a], patents must be made available by members of the WTO signatory to TRIPS “for any inventions, whether products or processes, in all fields of technology, provided that they are new, involved an inventive step and are capable of industrial application.”  Under Article 28(b), a patent must confer upon its owner the exclusive right “where the subject matter of a patent is a process, to prevent third parties not having the owner’s consent from the act of using the process, and from the acts of : using, offering for sale, selling, or importing for these purposes at least the product obtained directly by that process.”  Now that China is a member of the WTO, it appears that Chinese courts should construe the process claims of CN1057464 as covering the products of the process, including sildenafil. 

            The CN1057464 patent appears to in force until 2011 as it was applied for 19 June 1991 and under the Patent Law of the People’s Republic of China, Article 42, the term of a patent is 20 years from the date of filing.  CN1057464, application number 91104162, is listed by number, author and title in the SIPO database, which facts correspond with those for EP0463756.  This patent number is also cross-indexed to the abstract of patent EP0463756 in Chemical Abstracts [n8].   Therefore, depending upon the degree to which patents are construed in compliance with TRIPS by Chinese courts, this Chinese national patent should protect the composition of matter of sildenafil along with its use in treatment of angina.  If in force, as it appears to be, it has the effect of legally blocking any unauthorized manufacture, use, sale or import of sildenafil in China until 2011.  Thus, sildenafil as a chemical entity appears to be protected by patent at the present time in China, if Chinese courts are bound by the terms of the TRIPS treaty.

               It was not until a few years after the first synthesis of sildenafil that the utility of sildenafil in treatment of ED was discovered at Pfizer.   The course of the work leading to this discovery has been well described [n9]; however the essence of the finding was that sildenafil acts largely on one form (type V) of c-GMP phosphodiesterase enzyme found in the smooth muscle tissue of the penis, not in heart muscle.  This smooth muscle tissue controls the filling of the corpus cavernosum structures in the penis with blood that results in erection.  

               Several patent applications were filed by Pfizer disclosing and claiming this previously undisclosed use for sildenafil for treatment of ED.  Pfizer filed a PCT application [n10] on 13 May 1994 disclosing and claiming only the use of a series of pyrazolopyrimidinones including sildenafil for the treatment of impotence.  The range of chemical structures for which this use is claimed in the 1994 PCT application, publication number WO9428902, is comparable to the combined range of structures claimed as compositions of matter in the two earlier European patents, EP0463756 and EP0526004.

               It was national and regional phase patents derived from this PCT application that were invalidated in China this last year, and in the UK (EP patent), Columbia, and Venezuela within the preceding couple of years [n11].  It has been asserted in the press [n12] that the basis of invalidation of the patents in the South American countries was the same as for the UK version.  European Patent EP0702555 [n13], derived from WO9428902, is whose invalidation was upheld by the Chancery Division of the UK Patents Court [n1] in a suit brought by Lilly ICOS LLC in 1999.  The invalidation was upheld in 2000 and a full public record of the basis for the invalidation is available.

               China Patent No. CN1124926, also derived from WO9428902, application date 13 May 1994, granted in China 19 Sept. 2001, is the patent invalidated by the SIPO [n14] in 2004.  However, beyond a brief statement provided by the Chinese Patent Reexamination Board, the full legal basis for China’s invalidation of the Viagra use patent has apparently not yet been provided to the public by the Board [n14].

Legal Basis of Invalidation of the UK Sildenafil Use Patent

            European Patent No. EP0702555, entitled “Pyrazolopyrimidinones for the Treatment of Impotence” [n13] comprises 11 claims, all claims but one being directed to the use of chemical compounds of some defined type for manufacture of a medicament for the curative or prophylactic treatment of erectile dysfunction in males.  The first independent claim, claim 1, claims the use for treatment of ED of a set of compounds including an enormous number of individual molecular structures comprising both the amidosulfonylphenyl types including sildenafil and a wide variety of non-amidosulfonylphenyl types of pyrazolopyrimidinones.  Dependent claims 2-4 claim the use of increasingly smaller subsets of the full range of structures, dependent claim 5 claims the use of nine specific molecular species, claims 6 and 7 each claim use of one distinct chemical entity, claim 6 being directed to sildenafil and claim 7 to an analog.  Claim 8 claims pharmaceutically acceptable salts and formulations of any of the compounds of claims 1-7 for curative or prophylactic treatment of female sexual dysfunction; claim 9 claims oral treatment using any of the structures or for any of the uses specified in claims 1-8.  Claims 10 and 11 claim compounds not limited at all by structural class, but rather by biochemical activity.  These two claims are directed to the use for the curative or prophylactic oral treatment of ED in man of any compound that is an inhibitor of c-GMP PDE (claim 10) or any inhibitor specific for inhibition of the enzyme subclass of c-GMP PDE type V (claim 11).

            In 1999, Lilly ICOS LLC brought suit in the UK to invalidate EP0702555, asserting that the patent was improperly granted.  The claims that most concerned Lilly ICOS [n1, paragraph 38], and likely provided the main impetus for the filing of the invalidation suit by Lilly ICOS, were claims 10 and 11.  These claims arguably blocked use, manufacture or sale of tadalafil, Cialis®, Lilly’s ED treatment drug which acts on the same enzyme, although it is very different structurally.  The third medicine presently available for ED treatment, GlaxoSmithKline’s vardenafil, Levitra®, is a closer structural analog of sildenafil (but is not a pyrazolopyrimidinone or within the scope of the Pfizer patents) and works by the same mechanism, but vardenafil’s inventor was not party to the suit. 

            The EP0702555 patent was invalidated in its entirety based on a determination of obviousness of all the claims.  The Court found all claims obvious in view of a paper by Rafjer [n15], with further support for obviousness to be found in Murray [n16].  The Court held that Rafjer disclosed that the relaxation of human corpus cavernosum tissue (well known to result in an erection) under stimulation by electricity (mimicking neural stimulation) or nitric oxide (the natural neurotransmitter) is enhanced by selective inhibition of c-GMP phosphodiesterase.  The Rafjer reference alone was held to be sufficient, taken together with the knowledge of a worker of average skill in the field, to invalidate for obviousness all claims, not just claims 10 and 11, in EP0702555, insomuch as all the compounds for which ED treatment use were claimed had already been disclosed in the earlier EP0463756 and EP0526004 patents as inhibitors of this enzyme.  Further support for the holding of obviousness was found in the Murray paper, which disclosed the use of compounds that inhibited the breakdown of cGMP, rather than increasing the production of cGMP or of nitric oxide, for treatment of impotence.  Curiously, the basis for the invalidation of claim 8, for use of sildenafil and its analogs for treatment of female sexual dysfunction, was not provided in the opinion of the Court.

            In a closely reasoned argument, the Court provided a rational basis for the conclusion that the other ten claims of the EP0702555 patent were obvious under the well-defined and respected legal standards of British courts, as applied to treatment of ED in males.  While some may disagree with the outcome, it seems that few would argue that the decision reflects a domestic bias when adjudicating the validity of foreign-owned intellectual property.

Invalidation of the Sildenafil Use Patent in the People’s Republic of China

            The PCT application WO9428902, which designated China among other countries as where the application would be further submitted into the national/regional phases, was submitted into the national phase in China before the State Intellectual Property Office, application number 94192386, resulting in Chinese publication number CN1124926, granted on 19 Sept. 2001.  This patent asserts the PCT application date of 13 May 1994.  The patent would have remained in force 20 years, thus expiring in 2014, because a Chinese patent application claimed the priority date of the PCT application is treated under Chinese patent law in accordance with that treaty, under the Patent Law of China (Article 18) and the Implementing Regulations of the SIPO [n17].

            It should be noted that there is only a three-year difference between the 2011 expiration date of CN1057464 claiming a process for manufacturing sildenafil, and thus under the provisions of TRIPS also covering the sildenafil composition of matter, and the 2014 expiration date of CN1124926, the sildenafil use patent invalidated in the summer of 2004.  After 2014, the use of sildenafil for treatment of ED would have entered the public domain in China even had CN1124926 not been invalidated.

            Under the Patent Law of China, Article 45, any entity or individual may request the Patent Reexamination Board to declare a patent right invalid.  It was reported [n18] that the requesters in the present case were domestic Chinese manufacturers of generic pharmaceuticals, who asserted invalidity of the patent on a variety of bases including non-compliance with Article 26 or Article 22 of the Patent Law of China.  Article 26, paragraph 3, is roughly equivalent to 35 USC §112 or PCT Article 5, requiring a patent to provide sufficient enablement for a person skilled in the relevant field of technology to carry out the invention.  Article 22 requires novelty, inventiveness and practical applicability to exist for patent rights to be granted in an invention.  The novelty requirement under Chinese law is roughly parallel to the requirements of 35 USC §102(a), (b) and (e), or PCT Article 33(2), in that the identical invention may not, before the date of filing, have been publicly disclosed in publications in China or abroad, or been publicly used or made know to the public by any other means in China, or have been described by another person in a patent application filed before but published after the filing of the present application.  The practical applicability requirement is analogous to 35 USC §101 or PCT Article 33(4) concerning patentable subject matter.  The inventiveness requirement is analogous to 35 USC §103, or to PCT Article 33(3), and is defined by the Patent Law of China to mean that as compared with the technology existing before the date of filing, the invention sought to be patented “has prominent substantive features and represents a notable progress” [n7].

            This sildenafil use patent, when invalidated by the Patent Reexamination Board, was briefly stated by the Board to have failed to comply with Article 26, the enablement requirement [n14].  As no more detailed explanation or justification for the decision has been released to the public at the time of writing of this article, just how the patent failed to enable a person of ordinary skill in the art to practice the invention is unclear.  The patent discloses the exact chemical structure of sildenafil, and claims the oral administration thereof for treatment of ED in males.  A method of preparation for sildenafil was previously disclosed in EP0463756 (Example 12), which was cited in the present PCT application.  There have been allusions in press reports to the imposition of requirements for additional data by the SIPO subsequent to entry of the PCT application into the China national phase [n19].  However, no exact description provided to the public of what enabling data is considered to be missing by SIPO has been found to date.  It is puzzling how the patent could fail on enablement unless the Chinese language application was very different in scope from the PCT application it derived from.

            An appeal from an administrative act of the Patent Reexamination Board (either invalidation or refusal to invalidate) is provided for under Article 46 of the Patent Law of China, which allows either the patentee or a party who made the request for invalidation to appeal for judicial review in a People’s Court under the terms of China’s Administrative Procedure Law [n20, Article 14(1)].  The People’s Courts have jurisdiction to “examine to determine whether the specific administrative act is legal” [n20, Article 5].  The review proceedings are inter partes, as the People’s Court where the administrative appeal is heard is required to notify the opponent party to appear in the proceedings along with the administrative agency.  Pfizer is reported to have filed such an appeal within the required time limit of three months [n11b]. 

            Intellectual property rights cases on appeal from the SIPO are generally heard in Beijing’s No. 1 Intermediate People’s Court [n21], where a panel consisting of 3, 5 or 7 judges hears patent dispute cases.  Subsequent appeals from the holding of the initial judicial review, if desired, are generally heard in the Beijing Higher People’s Court [n22].  Under Chinese law, only one appeal from a judicial ruling is available [n23], so in the case of a patent appeal, only a single appeal to a higher court from the initial decision of a People’s Court in reviewing the Patent Reexamination Board’s administrative act may be had.  Thus, even though the Supreme People’s Court is the highest court in the land, most judicial appeals of Patent Reexamination Board administrative acts could never come before it.  Only those few patent cases significant enough to be first heard at trial in the Higher People’s Court may be appealed to the Supreme People’s Court [n22].

            Under the Administrative Procedure Law of the People’s Republic of China, Article 54, the People's Court may take one of several actions after hearing the case: (1) uphold the specific administrative act if the evidence is conclusive and the application of the law and regulations is correct, (2) rule to cancel or cancel partially the specific administrative act, or (3) rule to require the administrative agency to make a new administrative act if the specific administrative act has been found to be inadequate in essential evidence, if the application of the law or regulations has been found to be erroneous, if legal procedures were violated, or if the administrative agency exceeded its authority or abused its powers.

            In the present case, it would thus be among the lawful actions available to the People’s Court hearing the appeal to order the Patent Reexamination Board to modify the basis on which the sildenafil use patent was invalidated if it finds that the factual or legal basis provided by the Board for the invalidation is insufficient but affirms the invalidation.  Thus, even if Pfizer successfully argues at trial that the invalidated patent was in fact fully enabling, as indeed it might appear to be, the People’s Court may direct the Board to find that the patent is invalid on the basis of non-compliance with Article 22 rather than of Article 26 of the Patent Law of China, specifically for lack of inventiveness.  By substituting the new basis of invalidation, the Court could thus achieve the same result but bring the reasoning more in line with holdings of a well-respected court, the British Patent Court.  Indeed, the case made in the UK invalidation proceedings provides a ready-made basis for invalidation of the equivalent Chinese patent while at the same time defusing charge of domestic bias in intellectual property decisions.

            Although not directly germane to the legal validity or invalidity of the use patent CN1124926, the current interpretation of the earlier Chinese national patent CN1057464 on the pharmaceutical molecular entity sildenafil is relevant to the net effect that upholding the invalidation of the sildenafil ED use patent would have on the overall coverage enjoyed by Pfizer in China for sildenafil.  Just how the present Chinese courts might construe this patent in the context of the appeal of the invalidation of the sildenafil ED treatment patent remains to be seen.  For China to be in compliance with TRIPS, it must allow patent claims directed to products as well as processes [n24a].

            At the time of writing, few details are available concerning when the first judicial review by the Beijing No. 1 Intermediate People’s Court will take place or when their opinion will be issued.  Doubtless this will be watched with great interest.


            At the present time, China is moving aggressively to improve its image in the area of protection of intellectual property.  New initiatives to protect intellectual property in China with increased penalties for violations, increased education of the judiciary and the public as to the importance of IP, and increased availability of judicial remedies for infringement have recently been announced [n24b].  It is important to China’s international legal reputation for the invalidation of the sildenafil use patent to be supported by solid evidence and sound legal reasoning, and not to appear to be a cynical accommodation by China’s government of the interests of domestic manufacturers.  It has been pointed out that the fact that the domestic manufacturers of pharmaceutical substances in China took legal action to invalidate the patent rather than merely manufacturing pirated versions of the drug is significant, signaling as it may that the industry in China is being pressured to increase adherence to legal procedure [n25].

            The facts that existing patent protection for sildenafil apparently remains in legal effect in China until 2011, and the expiration of the invalidated patent would have come only three years later, suggests that the stakes for Pfizer in this dispute are not as great as one might be expected to infer from the numerous criticisms of China’s action, including those by a spokesperson for the U.S. Trade Representative [n26].  Rather, the stakes appear to be higher for China in their bid for global acceptance of the Chinese legal system as adequate to protect generally recognized international patent rights.  This case is an opportunity for China to demonstrate its renewed commitment to the standards of the TRIPS treaty and the accepted practices of the international scientific and technological business community by providing a firm judicial basis for its legal actions in this arena.

©Geoffrey K. Cooper 2004

[n1]      In the Matter of European Patent No. 0,702,555, High Court of Justice, Chancery Division, Patents Court, 8 November 2000, Case No. NC 1999 No 01110.

[n2]      These two European patents claim compositions of matter directed to amidosulfonylphenylpyrazolopyrimidinones including sildenafil and to non-amidosulfonylphenyl derivatives, and their uses for treatment of angina.  EP0463756 claims the amidosulfonylphenyl derivatives, closely comparable in breadth to the structural coverage of U.S. Patent Nos. 5,250,534 and 5,346,901 [n3], whereas EP0526004 claims the rest of the non-amidosulfonylphenyl structural classes also claimed in WO9428902, analogous to the coverage in U.S. Patent Nos. 5,272,147 and 5,426,107.

            European Patent EP0463756, 2 Jan. 1992, “Pyrazolopyrimidinone Antianginal Agents,” inventors Andrew Simon Bell, David Brown, Nicholas Kenneth Terrett; applicant Pfizer, Inc., filed 7 June 1991, discloses and claims pyrazolopyrimidinone sulfonamide derivatives of which sildenafil is an example.  This patent claims the priority of GB9013750, 20 June 1990.  It also claims use of the compounds for treatment of angina, hypertension, heart failure, atherosclerosis, stroke, peripheral vascular disease, conditions of reduced blood vessel patency, chronic asthma, bronchitis, allergic asthma, allergic rhinitis, glaucoma or diseases characterized by disorders of gut motility. 

            European Patent EP0526004, 3 Feb. 1993, “Pyrazolopyrimidinone Antianginal Agents, inventors Andrew Simon Bell and Nicholas Kenneth Terrett; applicant Pfizer, Inc., filed 2 July 1992, discloses and claims a broader set of the general class excluding the previously claimed sulfonamide genus of which sildenafil is a species.  This patent claims the priority of GB9114760, 9 July 1991. 

[n3]      U.S. Patent No. 5,250,534, 5 Oct. 1993, “Pyrazolopyrimidinone Antianginal Agents,” inventors Andrew S. Bell, David Brown, Nicholas K. Terrett; assignee Pfizer, Inc.; filed 14 May 1992. Corresponding to EP0463756, this patent discloses and claims pyrazolopyrimidinone sulfonamide derivatives of which sildenafil is an example, likewise claiming the priority of GB9013750.  U.S. Patent No. 5,346,901, 13 Sept. 1994, a divisional of the above patent of the same title discloses and claims sulfonamide analogs wherein the 4-N-methylpiperazine moiety of sildenafil is replaced by a pyrrolidino, piperidino, or morpholino group.  Both patents claim the use of their respective compounds for treatment of angina, hypertension, heart failure or atherosclerosis. 

            U.S. Patent No. 5,272,147, 21 Dec. 1993, “Pyrazolopyrimidinone Antianginal Agents,” inventors Andrew S. Bell and Nicholas K. Terrett; assignee Pfizer, Inc.; filed 12 June 1992.  Corresponding to EP0526004, this patent discloses and claims a broader set of the general class excluding the previously claimed sulfonamide genus of which sildenafil is a species, likewise claiming the priority of GB9114760.  The compounds are claimed for use in treatment of angina, hypertension, pulmonary hypertension, congestive heart failure or atherosclerosis.  U.S. Patent No. 5,426,107, 20 June 1995, a divisional of the above patent of the same title claims this same broader set of pyrazolopyrimidinones for treatment of stroke, peripheral vascular disease, conditions of reduced blood vessel patency, chronic asthma, bronchitis, allergic asthma or allergic rhinitis.

[n4]      None found on the esp@cenet search engine at, searching “pyrazolopyrimidinone” and “antianginal,” or the INPADOC family for EP0463756 [n6].

[n5]      International Publication No. WO9306104, 1 April 1993, from International Application No. PCT/EP92/02068, filed 4 Sept. 1992.  WO9306104 concerns only pyrazolopyrimidinone derivatives wherein the pyrazole ring is C-substituted with a methyl group, whereas in sildenafil a propyl group occupies this position.

            International Publication No. WO9307149, 15 April 1993, from International Application No. PCT/EP92/02237, filed 24 Sept. 1992.  WO9307149 concerns only pyrazolo-[3,4-d]-pyrimidinones that are isomeric with the [4,3-d] family that includes sildenafil.

[n6]      The INPADOC family for EP0463756 shows the following equivalents: AU626757, AU7915591, BR9102560, CA2044748, CN1028758B, CN1057464, CS9101876, CY1971, CZ279289, DE69108991D, DE69108991T, DK463756T, EG19651, ES2071919T, FI913017, FI95132B, FI95132C, HK219496, HU218945, HU61312, IE66040, IE912094, IL98482, JP2087736C, JP6041133, JP7121945B, KR9406628, LU90360, NL990005I, NO178029B, NO178029C, NO912366, NZ238586, PL166490B, PL290721, PT98011, RU2047617, RU2114114, ZA9104707. 

[n7a]    The Patent Law of the People’s Republic of China, as amended, first entered into force 1 April 1985.  In 1992 the Patent Law was amended to allow pharmaceutical products and substances obtained by means of a chemical process to receive patent protection. “Protecting Drug Developers,” Xiao Xin, China Daily, 2004-05-31, page 5, .

[n7b]    Translated by Xiaodan (Amber) Sun, patent attorney, reg. no. 55,655.

[n8]      Chemical Abstracts 116:255626q, Jan.-Jun. 1992.

[n9]      For example, see or many other similar articles from a Google search of “sildenafil discovery.”

[n10]    PCT/EP94/01580 filed 13 May 1994, International Publication No. WO9428902, published 22 Dec. 1994, “Pyrazolopyrimidinones for the Treatment of Impotence,” inventors Peter Ellis and Nicholas Terrett, applicant Pfizer, Inc., claiming priority of GB9311920.4, 9 June 1993.  The range of chemical structures as disclosed in WO9428902 as useful for treatment of impotence is close but not identical to the range of chemical structures claimed in the original work on treatment of angina.  It covers both the amidosulfonylphenyl- (including sildenafil) and non-amidosulfonylphenyl-substituted pyrazolopyrimidinones.

[n11a] “The Hoopla over Viagra Patenting in China,” Andy Ho, Straights Times, July 16, 2004; .

[n11b] “Viagra patent challengers,” 21st Century Online, July 15, 2004, .

           “Patent on Viagra faces challenge,” Liu Li, China Daily, 29 Sept. 2004, .

[n12]    “China Revokes Viagra Patent,” Duan Hongqing, Zhu Xiaochao and Fu Li’ao, Caijing English newsletter, July 20, 2004, .

[n13]    EP0702555, inventors Peter Ellis and Nicholas Kenneth Terrett, European regional phase patent derived from PCT/EP94/01580, WO9428902, 11 Mar. 1998, see [n10].

[n14]    “Authorities: Viagra patent found invalid,” Guo Nei, People’s Daily Online, July 9, 2004.  Source: China Daily .

[n15]    “Nitric oxide as a mediator of relaxation of the corpus cavernosum in respect to nonadrenergic, noncholinergic neurotransmission,” Rafjer et al., New England Journal of Medicine, 362(2), 90, 9 Jan. 1992.

[n16]    “Phosphodiesterase VA Inhibitors,” Murray, K.G., Drug News and Perspectives, 6(3), 150-6, April 1993.

[n17]    Implementing Regulations of the Patent Law of the People’s Republic of China, Rule 100.

[n18]    “Viagra’s China Patent a Fizzer,” Phelim Kyne, Wall Street Journal, July 9, 2004.  This source reports that challengers asserted lack of novelty, Article 22 of Patent Law of China.

            “Dispute Regarding Revocation of Pfizer’s Viagra Patent in China,” Minakshi Poddar, news, 6 Aug. 2004, .  This source reports that challengers asserted lack of enablement, Article 26 of Patent Law of China.

[n19]    “China challenging drug patents,” Paul Mooney, The Scientist, 20 Aug. 2004, .

[n20]    Administrative Procedure Law of the People’s Republic of China, .

[n21]    “China’s Court to Begin Handling Patent Disputes,” People’s Daily, July 21, 2001, .

            “Judicial Protection of IPR in China,” Zhipei Jiang, Justice, Supreme People’s Court of China, .

[n22]    “Judicial Protection of IPR in China,” Zhipei Jiang, Justice, Supreme People’s Court of China, .

[n23]    Civil Procedure Law of the People’s Republic of China, Article 158. “The judgments and orders of a people's court of second instance shall be final. ” .

[n24a] TRIPS, Article 27:  Patentable Subject Matter 1. Subject to the provisions of paragraphs 2 and 3, patents shall be available for any inventions, whether products or processes, in all fields of technology, provided that they are new, involve an inventive step and are capable of industrial application.

Article 28:  Rights Conferred:  A patent shall confer on its owner the following exclusive rights: (a) ... (b) where the subject matter of a patent is a process, to prevent third parties not having the owner’s consent from the act of using the process, and from the acts of: using, offering for sale, selling, or importing for these purposes at least the product obtained directly by that process. 

[n24b] For example:

            “Regulation of People’s Republic of China on Customs Protection of Intellectual Property Rights,” Order of the State Council of the People’s Republic of China, no. 395, enacted March 1, 2004:  Article 3. PRC prohibits import and export of goods infringing IPR.

  , sponsored by the Supreme People’s Court of the PRC, “Violation of IPR now major crime,” Dec. 22, 2004.

            “Judicial Protection of Intellectual Property in China and its Prospects,” Zhipei Jiang, Justice, Supreme People’s Court of China, 16 May 2004,

            “Tougher penalties set out for IPR piracy,” De Sheng, China Daily, 23 Dec. 2004, .

[n25]    Peter K. Yu, “Viagra’s Upside: Rejecting Pfizer’s patent was a sign of progress in China,” IP Law and Business, Oct. 2004.

[n26]    “Fertile Ground for a Patent War,” Allen T. Cheng, International Herald Tribune, 20 Aug. 2004, .

*Geoffrey K. Cooper is a registered Patent Attorney (reg. no. 51,266) and member of the Oregon Bar.  He holds a Ph.D. in organic chemistry, specializing in synthetic methods development, from the University of Oregon.  Dr. Cooper worked in senior research positions with large corporations including Atlantic Richfield, Montedison, and Zeneca, as well as with the biotech startup Oncologic.  After obtaining a J.D. from the University of Oregon School of Law, he entered private legal practice involving the prosecution of patents in all fields, trademark matters, and unfair trade practices.

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