## Facts

- Teva owned patents covering a manufacturing method for Copaxone, a multiple sclerosis drug whose active ingredient is a mixture of polypeptides.
- The patents claimed, among other limitations, that the active ingredient had “a molecular weight of 5 to 9 kilodaltons.”
- Sandoz and other generic manufacturers argued the “molecular weight” limitation was indefinite under 35 U.S.C. § 112 because it did not specify which of three measures of molecular weight applied (peak average, number average, or weight average).
- In a Markman hearing, the district court heard conflicting expert testimony about how a person of ordinary skill in the art would understand “molecular weight” in context.
- The district court credited Teva’s expert and made a factual finding that a skilled artisan would read “molecular weight” as referring to peak average molecular weight (Mp), concluding the term was sufficiently definite.

## Issues

1. What standard of review must the Federal Circuit apply to a district court’s subsidiary factual findings made during patent claim construction.
2. Whether Federal Rule of Civil Procedure 52(a)(6) requires clear-error review of those factual findings, as opposed to de novo review.

## Decision

- The Supreme Court vacated the Federal Circuit’s judgment and remanded.
- The Court held that when a district court resolves subsidiary factual matters in construing a patent claim, the Federal Circuit must review those factual findings for clear error.
- The Court reaffirmed that the ultimate construction of a patent claim remains a question of law reviewed de novo.
- The Court concluded the Federal Circuit erred by rejecting the district court’s expert-based factual finding without applying clear-error review.

## Legal Principles

- Federal Rule of Civil Procedure 52(a)(6) requires appellate courts to review district court findings of fact under the clear-error standard, without a patent-specific exception.
- Claim construction may involve both:
  - legal determinations based on intrinsic evidence (claims, specification, prosecution history), reviewed de novo; and
  - subsidiary factual findings based on disputed extrinsic evidence (including expert testimony about technical meaning to skilled artisans), reviewed for clear error.
- Markman assigns claim construction to judges, but does not convert all components of claim construction into purely legal determinations for de novo review.

## Conclusion

The Supreme Court held that appellate review of claim construction is mixed: the Federal Circuit reviews the ultimate claim meaning de novo, but must defer under clear-error review to a district court’s subsidiary fact findings grounded in disputed extrinsic evidence, and it vacated and remanded for review under that standard.


Teva Pharms. USA, Inc. v. Sandoz, Inc., 135 S. Ct. 831 (2015)