United States: Equivalence In Chemical Cases

In Mylan Institutional LLC et al. v. Aurobindo Pharma Ltd. et al., 2017-1645 (May 19, 2017), the Federal Circuit attempted to clarify the application of the doctrine of equivalents in chemical cases. Although affirming a district court grant of a preliminary injunction on a patent directed to isosulfan blue (ISB), a dye used for lymph node mapping, the court reversed the grant of the injunction to the extent it was based on two process patents. According to the Federal Circuit, the district court erred in determining that Mylan had demonstrated a likelihood of success in showing that Aurobindo infringes U.S. Patent 7,622,992 (the '992 patent) and U.S. Patent 8,969,616 (the '616 patent) because "the district court's analysis of equivalence in this case was flawed." Slip opinion at 12.

The '992 and '616 patents claim a process for preparing ISB comprising reacting isoleuco acid with silver oxide, recovering the ISB acid and treating the ISB acid with a sodium solution. Aurobindo's process (the accused process) for preparing ISB differs from the patented process in that manganese dioxide is used in place of silver oxide as an oxidizing agent. The district court found that the accused process likely infringed the patented process under the doctrine of equivalents. Aurobindo argued on appeal that the district court erred, because manganese dioxide is a strong oxidizing agent that requires use of an acid, whereas silver oxide is a weak oxidizing agent that does not require an acid. Thus, according to Aurobindo, manganese dioxide and silver oxide oxidize isoleuco acid in different ways. Mylan countered, arguing that in the context of the process patents, silver oxide and manganese dioxide are equivalent. Mylan supported its assertion with expert testimony that the crude ISB yield from both the silver oxide and manganese dioxide processes is similar, a result that Mylan contended would not be expected if silver oxide and manganese dioxide were substantially different.

The Federal Circuit first noted that the "law on the doctrine of equivalents as applied to chemical materials is not clear, and its misapplication can lead to unsound results." Id. Agreeing that the Supreme Court, in Graver Tank & Mfg. Co. v. Linde Air Prod. Co., 339 U.S. 605, 608, 609 (1950), had identified the function-way-result (FWR) test and the insubstantial differences test as two reasonable bases for an equivalence analysis, the Federal Circuit further acknowledged that the later case of Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 39 (1997) stated that "non-mechanical cases may not be well-suited to consideration under the FWR test. That seems to be particularly true in the chemical arts." Slip opinion at 13. The Federal Circuit noted, however, that Warner-Jenkinson Co. also indicates that "the suitability of the two tests may vary, depending on the circumstances of the case[,]" and that "[d]ifferent linguistic frameworks may be more suitable to different cases, depending on their particular facts." Id. (quoting Warner-Jenkinson Co., 520 U.S. at 40). Thus, the Federal Circuit concluded that the Supreme Court "seemingly blessed two equivalents tests, leaving to the lower courts in future cases the choice of which to apply." Slip opinion at 13.

Some of the difficulty in applying the FWR test in chemical cases arises, according to the Federal Circuit, because it is applied on a limitation-by-limitation basis, and with "chemical compositions having many components, chemical compounds with many substituents (which are usually claimed as separate limitations), and those having a medical or biological use, it is often not clear what the 'function' or 'way' is for each claim limitation." Id. at 14. The Federal Circuit further explained that in chemical process claims, the "function" and "way" of a claim limitation "may remain vague and often overlap[,]" or "may be synonymous." Id. at 15. The Federal Circuit further implied that the "result" prong of the FWR test may be of limited use in chemical cases because, although "the structure and uses of one compound may be directly compared with those of another[,]" infringement under the FWR test is determined on a limitation-by-limitation basis. Id. at 14.

The Federal Circuit concluded that the district court's application of the FWR test was flawed because the district court failed to properly address the "way" prong of the FWR test. Although the district court correctly identified oxidation of isoleuco acid as the function of silver oxide in the patented process, it dismissed as irrelevant, under either the FWR or insubstantial differences tests, Aurobindo's argument that the oxidation strength of silver oxide is different from that of manganese dioxide. In the district court's view, the absence of any claim limitation on oxidation strength rendered the relative oxidation strengths irrelevant. According to the Federal Circuit, the district court either failed to analyze the "way" prong of the FWR test or, if it did analyze "way," failed to account for the relative oxidation strengths of silver oxide and manganese dioxide or the use of acid when using manganese dioxide. Thus, the Federal Circuit concluded "there is room for sufficient doubt as to whether silver oxide and manganese dioxide oxidize isoleuco acid in the same way so as to satisfy the 'way' prong of the FWR test." Id. at 16.

The Federal Circuit recommended that in trying the merits of the case, the district court consider whether the insubstantial differences test might be better suited to evaluating the equivalence. The court stated that "[e]ven if evaluating the 'function' and 'way' prongs is feasible, the FWR test may be less appropriate for evaluating equivalence in chemical compounds." Slip opinion at 16-17.

The Federal Circuit used a comparison between aspirin and ibuprofen in an attempt to demonstrate how "a compound may appear to be equivalent under the FWR test, but not under the substantiality of the differences test." Id. at 17. The court first noted that due to the compounds' substantial structural differences, "chemists would not usually consider [aspirin and ibuprofen] to be structural equivalents under the insubstantial differences test." Id. On the other hand, the FWR test would suggest that aspirin and ibuprofen are substantial equivalents, according to the Federal Circuit, because "each provide[s] analgesia and anti-inflammatory activity ('function') by inhibiting prostaglandin synthesis ('way') in order to alleviate pain, reduce fevers, and lessen inflammation ('result')." Id. In this example, however, the Federal Circuit does not identify the claim in which the aspirin or ibuprofen appears, and so it provides no context against which equivalence of aspirin and ibuprofen is to be evaluated.1

The court further noted that "the process patents recite a method for preparing a specifically named compound by combining another specifically depicted compound with a third specific compound, viz., silver oxide. Each of these compounds is expressly named, and an infringement analysis must not take lightly the specific recitation of these materials." Slip opinion at 17. The Federal Circuit further explained that "[m]anganese dioxide and silver oxide are substantially different in many respects. For example, manganese and silver are in different groups of the Periodic Table. In oxide form, manganese has an oxidation state of +4, while silver is +1. Those differences may well be relevant to equivalence at trial." Id. at 18.

The court's vague warning against taking lightly the recitation of specific materials, combined with its out-of-context, structure-based comparison of aspirin and ibuprofen, seems to suggest a focus on structural differences in chemical cases. If structural differences between two chemical compounds were sufficient to establish substantial differences and thus nonequivalence, however, then the doctrine of equivalents would appear to be quite limited, given that structural differences will necessarily exist between two nonidentical chemical compounds. Instead, it is likely that the context in which the chemical compound is claimed will guide assessment of whether a structural difference is substantial. For example, the structural differences between silver oxide and manganese dioxide that the court identifies as substantial, i.e., being in different groups in the periodic table and having different oxidation states, pertain to the different strengths of the compounds in the context of their use as oxidizing agents. As the court noted, a properly conducted FWR analysis would have taken into account these different oxidizing strengths as part of analyzing the "way" prong. In this case, therefore, it would appear that the FWR and insubstantial differences tests may in fact lead to the same conclusion.

In view of this case, the practitioner would be advised to assess equivalence in chemical cases under both the insubstantial differences test and the FWR test and, if needed, be prepared to justify the use of one test over the other. The context in which the limitation (e.g., chemical compound or structural substituent) is claimed and its function in the disclosed utility of the invention will be important.


1In addition, an equivalence analysis regarding the two analgesics may also need to assess whether the differences between the compounds result in a different degree or mechanism of inhibition.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

To print this article, all you need is to be registered on Mondaq.com.

Click to Login as an existing user or Register so you can print this article.

In association with
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Register for Access and our Free Biweekly Alert for
This service is completely free. Access 250,000 archived articles from 100+ countries and get a personalised email twice a week covering developments (and yes, our lawyers like to think you’ve read our Disclaimer).
Email Address
Company Name
Confirm Password
Mondaq Topics -- Select your Interests
 Law Performance
 Law Practice
 Media & IT
 Real Estate
 Wealth Mgt
Asia Pacific
European Union
Latin America
Middle East
United States
Worldwide Updates
Check to state you have read and
agree to our Terms and Conditions

Terms & Conditions and Privacy Statement

Mondaq.com (the Website) is owned and managed by Mondaq Ltd and as a user you are granted a non-exclusive, revocable license to access the Website under its terms and conditions of use. Your use of the Website constitutes your agreement to the following terms and conditions of use. Mondaq Ltd may terminate your use of the Website if you are in breach of these terms and conditions or if Mondaq Ltd decides to terminate your license of use for whatever reason.

Use of www.mondaq.com

You may use the Website but are required to register as a user if you wish to read the full text of the content and articles available (the Content). You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these terms & conditions or with the prior written consent of Mondaq Ltd. You may not use electronic or other means to extract details or information about Mondaq.com’s content, users or contributors in order to offer them any services or products which compete directly or indirectly with Mondaq Ltd’s services and products.


Mondaq Ltd and/or its respective suppliers make no representations about the suitability of the information contained in the documents and related graphics published on this server for any purpose. All such documents and related graphics are provided "as is" without warranty of any kind. Mondaq Ltd and/or its respective suppliers hereby disclaim all warranties and conditions with regard to this information, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. In no event shall Mondaq Ltd and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of information available from this server.

The documents and related graphics published on this server could include technical inaccuracies or typographical errors. Changes are periodically added to the information herein. Mondaq Ltd and/or its respective suppliers may make improvements and/or changes in the product(s) and/or the program(s) described herein at any time.


Mondaq Ltd requires you to register and provide information that personally identifies you, including what sort of information you are interested in, for three primary purposes:

  • To allow you to personalize the Mondaq websites you are visiting.
  • To enable features such as password reminder, newsletter alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our information providers who provide information free for your use.

Mondaq (and its affiliate sites) do not sell or provide your details to third parties other than information providers. The reason we provide our information providers with this information is so that they can measure the response their articles are receiving and provide you with information about their products and services.

If you do not want us to provide your name and email address you may opt out by clicking here .

If you do not wish to receive any future announcements of products and services offered by Mondaq by clicking here .

Information Collection and Use

We require site users to register with Mondaq (and its affiliate sites) to view the free information on the site. We also collect information from our users at several different points on the websites: this is so that we can customise the sites according to individual usage, provide 'session-aware' functionality, and ensure that content is acquired and developed appropriately. This gives us an overall picture of our user profiles, which in turn shows to our Editorial Contributors the type of person they are reaching by posting articles on Mondaq (and its affiliate sites) – meaning more free content for registered users.

We are only able to provide the material on the Mondaq (and its affiliate sites) site free to site visitors because we can pass on information about the pages that users are viewing and the personal information users provide to us (e.g. email addresses) to reputable contributing firms such as law firms who author those pages. We do not sell or rent information to anyone else other than the authors of those pages, who may change from time to time. Should you wish us not to disclose your details to any of these parties, please tick the box above or tick the box marked "Opt out of Registration Information Disclosure" on the Your Profile page. We and our author organisations may only contact you via email or other means if you allow us to do so. Users can opt out of contact when they register on the site, or send an email to unsubscribe@mondaq.com with “no disclosure” in the subject heading

Mondaq News Alerts

In order to receive Mondaq News Alerts, users have to complete a separate registration form. This is a personalised service where users choose regions and topics of interest and we send it only to those users who have requested it. Users can stop receiving these Alerts by going to the Mondaq News Alerts page and deselecting all interest areas. In the same way users can amend their personal preferences to add or remove subject areas.


A cookie is a small text file written to a user’s hard drive that contains an identifying user number. The cookies do not contain any personal information about users. We use the cookie so users do not have to log in every time they use the service and the cookie will automatically expire if you do not visit the Mondaq website (or its affiliate sites) for 12 months. We also use the cookie to personalise a user's experience of the site (for example to show information specific to a user's region). As the Mondaq sites are fully personalised and cookies are essential to its core technology the site will function unpredictably with browsers that do not support cookies - or where cookies are disabled (in these circumstances we advise you to attempt to locate the information you require elsewhere on the web). However if you are concerned about the presence of a Mondaq cookie on your machine you can also choose to expire the cookie immediately (remove it) by selecting the 'Log Off' menu option as the last thing you do when you use the site.

Some of our business partners may use cookies on our site (for example, advertisers). However, we have no access to or control over these cookies and we are not aware of any at present that do so.

Log Files

We use IP addresses to analyse trends, administer the site, track movement, and gather broad demographic information for aggregate use. IP addresses are not linked to personally identifiable information.


This web site contains links to other sites. Please be aware that Mondaq (or its affiliate sites) are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of these third party sites. This privacy statement applies solely to information collected by this Web site.

Surveys & Contests

From time-to-time our site requests information from users via surveys or contests. Participation in these surveys or contests is completely voluntary and the user therefore has a choice whether or not to disclose any information requested. Information requested may include contact information (such as name and delivery address), and demographic information (such as postcode, age level). Contact information will be used to notify the winners and award prizes. Survey information will be used for purposes of monitoring or improving the functionality of the site.


If a user elects to use our referral service for informing a friend about our site, we ask them for the friend’s name and email address. Mondaq stores this information and may contact the friend to invite them to register with Mondaq, but they will not be contacted more than once. The friend may contact Mondaq to request the removal of this information from our database.


This website takes every reasonable precaution to protect our users’ information. When users submit sensitive information via the website, your information is protected using firewalls and other security technology. If you have any questions about the security at our website, you can send an email to webmaster@mondaq.com.

Correcting/Updating Personal Information

If a user’s personally identifiable information changes (such as postcode), or if a user no longer desires our service, we will endeavour to provide a way to correct, update or remove that user’s personal data provided to us. This can usually be done at the “Your Profile” page or by sending an email to EditorialAdvisor@mondaq.com.

Notification of Changes

If we decide to change our Terms & Conditions or Privacy Policy, we will post those changes on our site so our users are always aware of what information we collect, how we use it, and under what circumstances, if any, we disclose it. If at any point we decide to use personally identifiable information in a manner different from that stated at the time it was collected, we will notify users by way of an email. Users will have a choice as to whether or not we use their information in this different manner. We will use information in accordance with the privacy policy under which the information was collected.

How to contact Mondaq

You can contact us with comments or queries at enquiries@mondaq.com.

If for some reason you believe Mondaq Ltd. has not adhered to these principles, please notify us by e-mail at problems@mondaq.com and we will use commercially reasonable efforts to determine and correct the problem promptly.