A Small Detail in the Specification May Save “Molecular Weight” from Being Held Indefinite: A Lesson from Reckitt Benckiser Pharm. Inc. v. Watson Labs.,Inc.

I. Introduction

35 U.S.C. § 112(b) requires that “[t]he speci-fication shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention.” ¹ The statute is known as the indefiniteness requirement. ² The standard of indefiniteness was settled in Nautilus, Inc. v. Biosig Instruments, Inc., ³ where the Supreme Court required courts to find whether “a patent's claims, viewed in light of the specification and prosecution history, inform those skilled in the art about the scope of the invention with reasonable certainty.” ⁴

In 2015, the Federal Circuit in Teva Pharms. USA, Inc. v. Sandoz, Inc. ⁵ (hereinafter Teva IV) held that “molecular weight” was an indefinite claim term for describing copolymer-1. ⁶ There, the disputed term was “a molecular weight of about 5 to 9 kilodaltons.” ⁷ The Federal Circuit found that the claim language and specification failed to tell whether “molecular weight” means a number-average molecular weight (M_n), weight-average molecular weight (M_w), or peak-average molecular weight (M_p). ⁸ Instead, the Federal Circuit found that the prosecution history of two family patents showed that “molecular weight” means an M_w or M_p. ⁹ Thus, the Federal Circuit found the disputed term indefinite. ¹⁰

The Teva IV decision indicates that “molecular weight” as a claim term in polymer-related patents may mean a number-average molecular weight, weight-average molecular weight, or peak-average molecular weight, if the specification fails to describe which definition is followed. ¹¹ The Teva IV decision also indicates that expert testimony may prove “molecular weight” to be definite, as long as the prosecution history of the disputed patent and its family patents does not show a different conclusion. ¹²

Teva IV acknowledges the complexity of “molecular weight” in polymer technology. The concept of “molecular weight” for polymers is “average.” ¹³ Because polymer molecules of the same kind have different lengths, it is impossible to characterize a polymer sample by a single molecular weight. ¹⁴ Rather, the molecular weight of a polymer sample is presented by an average of molecular weights of all polymer molecules in the sample. ¹⁵ As shown in Table 1, ¹⁶ there are several ways to define “average.” ¹⁷

Since Teva IV, whether “molecular weight” is an indefinite claim term has become an issue in litigation concerning polymer-related patents. ¹⁸ Reckitt Benckiser Pharm. Inc. v. Watson Labs., Inc. ¹⁹ (hereinafter, “Reckitt”) is one decision where the United States District Court for the District of Delaware disagreed with the defendants' indefiniteness challenge concerning “molecular weight” as a claim term describing polyethylene oxide. ²⁰ The lawsuit arose from two separate abbreviated new drug applications (ANDAs) for a generic version of Suboxone^® sublingual film that is used for treating opioid dependence. ²¹ Suboxone^® sublingual film was sold by Reckitt Benckiser Pharmaceuticals Inc., which was also an exclusive licensee of three asserted patents. ²² Two ANDA applicants were Watson Laboratories, Inc. and Par Pharmaceutical, Inc. which were the defendants in this case. ²³

The Reckitt court relied on a short sentence in the specification which describes the source of polyethylene oxide and found the term “molecular weight” definite. ²⁴ This article is intended to explore the Reckitt decision and argue that a small detail in the specification regarding the meaning of “molecular weight” may save claim term “molecular weight” from being held indefinite. Next, Part II analyzes the Reckitt decision and includes discussion of relevant legal doctrines. Part III discusses what can be learned from the Reckitt decision to improve the patent drafting practice.

II. Analysis of Reckitt Benckiser Pharm. Inc. v. Watson Labs., Inc.

C. District court's reasoning

Regarding the indefiniteness issue, the Reckitt court held that the defendants “failed to prove by clear and convincing evidence that a person skilled in the art would not know with reasonable certainty the meaning of ‘molecular weight’ in the context of the '150 patent.” ³⁷ Instead, the Reckitt court concluded:

In the absence of a specified method to measure molecular weight and in light of the patent's references to molecular weight as reported by Dow, I find that the weight of the evidence demonstrates that one of skill in the art would understand that the patent relies on the molecular weight of Polyox N80 reported by Dow as the measure of “molecular weight.” ³⁸

The Reckitt court reached its conclusion by considering the specification, the expert testimony, and the information of the infringing products. ³⁹ When construing a claim, courts rely on intrinsic evidence and extrinsic evidence. ⁴⁰ The intrinsic evidence covers claims, specification, and prosecution history, ⁴¹ while the extrinsic evidence includes “expert and inventor testimony, dictionaries, and learned treatises.” ⁴² Thus, the Reckitt court relied on both intrinsic and extrinsic evidence to resolve the indefiniteness issue.

The Reckitt court's reasoning can be divided into two categories. One category focuses on the specification, while the other focuses on the expert testimony.

When examining the specification, the Reckitt court found that “[t]he '150 patent does not explicitly describe a method to use to calculate molecular weight.” ⁴³ But the Reckitt court noticed that the specification states the source of polyethylene oxide is Dow Chemical Company. ⁴⁴ The Reckitt court further considered values listed in one table of the '150 patent (shown in Figure 1) as the approximate viscosity-average molecular weights assigned to different grades of polyethylene oxide, because it found that the accused ANDA drugs also used polyethylene oxide provided by Dow Chemical Company and that Dow Chemical Company assigned an approximate viscosity-average molecular weight to each polyethylene oxide product. ⁴⁵ Therefore, the Reckitt court held that “[a] person of ordinary skill in the art would understand the term ‘molecular weight’ in the patent to refer to viscosity average molecular weight as reported by the manufacturers of commercial [polyethylene oxide].” ⁴⁶

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FIG. 1.

Table 22 of the ’150 patent.

Regarding the expert testimony, the Reckitt court considered the opinions from both parties' experts. ⁴⁷ The defendants' experts showed that the molecular weight of a polyethylene oxide sample may have different definitions. ⁴⁸ The defendants' experts also testified that there are two different methods for measuring the average molecular weight of a polyethylene oxide sample and each method gives different numerical values for the molecular weight of the same sample. ⁴⁹ On the other hand, the plaintiff asserted that “molecular weight” means viscosity-average molecular weight. ⁵⁰ Finally, the Reckitt court disagreed with the defendants' experts, ⁵¹ because “[t]he claims are not indefinite merely because multiple methods of measuring molecular weight exist.” ⁵²

III. Patent Drafting

The Reckitt decision suggests that a small detail in the specification may save the term “molecular weight” in a polymer-related claim from being held indefinite. The specification of the '150 patent mentions the source of polyethylene oxide. But, the relevant statement is not in the main text. Rather, the source of polyethylene oxide is disclosed as a footnote of one table (shown in Figure 2), while such table is used for describing the compositions of the test samples. ⁵³

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FIG. 2.

Table 21 of the ’150 patent.

The exact information in the '150 patent regarding the source of polyethylene oxide is only the phrase “Available from Dow Chemical Company,” which is not even a full sentence. ⁵⁴ The phrase does not explain which “molecular weight” the '150 patent refers to. During the Markman hearing, the plaintiff actually argued that “molecular weight” meant “actual molecular weight” (or “the sum of the atomic weights of all the atoms in a molecule”). ⁵⁵ That argument clearly contradicted the plaintiff's later argument for the definiteness of “molecular weight.” Eventually, the district court adopted the defendants' approach and construed “molecular weight” as “average molecular weight.” ⁵⁶ The district court further left the question of whether “molecular weight” means “viscosity-average molecular weight” to a later proceeding regarding the indefiniteness issue. ⁵⁷

Although “molecular weight” in the claims of the '150 patent is not indefinite, the patent drafting of the '150 patent is risky. The Reckitt court did not directly hold “molecular weight” definite. ⁵⁸ Instead, the Reckitt court had to rely on extrinsic evidence. ⁵⁹ That is, whether “molecular weight” is indefinite depends on extrinsic evidence developed during litigation. Expert testimony is helpful, but it does not work out well in every case. The Reckitt court did not rely on the plaintiff's expert testimony to conclude that “molecular weight” means “viscosity-average molecular weight.” ⁶⁰ Instead, the Reckitt court quoted the defendants' expert testimony to support its holding. ⁶¹

Another example similar to the '150 Patent is U.S Patent No. 6,348,469 (the '469 patent) with the title “solid compositions containing glipizide and polyethylene oxide.” Claim 2 of the '469 patent recites “[t]he composition according to claim 1, in which the polyethylene oxide has a molecular weight which varies from 50,000 to 8,000,000.” ⁶² The specification states: “Polyethylene oxide referred to as PEO below is moreover known as a component of medicaments in tablet form designed to be administered by oral route. This compound is marketed by the Union Carbide Corporation under the commercial name Polyox^®.” ⁶³

But the specification does not identify whether “molecular weight” means “average molecular weight” or which average molecular weight the term refers to. ⁶⁴ So, when an indefiniteness issue is raised, the patentee may have to present extrinsic evidence, such as product documents from Union Carbide Corporation, to explain that “molecular weight” means a certain class of average molecular weight.

The risk of indefiniteness can be avoided if the drafter of the '150 patent would have taken another approach. According a product document of polyethylene oxide from Dow Chemical Company, the approximate molecular weight of each polyethylene oxide grade is “[b]ased on rheological measurements.” ⁶⁵ The document further states that “[m]olecular weights obtained by other methods, including light scattering and gel permeation chromatography, may not be directly comparable.” ⁶⁶ By using “rheological measurements” to define the molecular weight of polyethylene oxide, the term “molecular weight” clearly means “viscosity-average molecular weight.” ⁶⁷ The concern of the indefiniteness of “molecular weight” will be eliminated.

V. Conclusion

After Teva IV, “molecular weight” has become a disputable term in a polymer-related claim. When the specification does not define the meaning of “molecular weight,” the patentee has to rely on expert testimony to resolve the indefiniteness issue of “molecular weight.” The Reckitt decision suggests that a small detail in the specification may save “molecular weight” from being held indefinite. Such small detail may just be a footnote indicating the source of the polymer material related to the disputed term “molecular weight.” But the question is that the patentee has to depend on the court's view on expert testimony. Therefore, the best way is to not only provide the source but also state the specific average molecular weight assigned to the polymer material.