Background
AstraZeneca holds patents covering Symbicort®, a pressurized metered-dose inhaler used to treat asthma and COPD. One of the key patents claimed a formulation containing polyvinylpyrrolidone (PVP) as a stabilizer at a concentration of “0.001%.” AstraZeneca sued Mylan Pharmaceuticals in the Northern District of West Virginia after Mylan sought FDA approval to sell a generic version of Symbicort. The district court construed “0.001%” broadly to include any concentration within one significant figure — that is, ranging from 0.0005% to 0.0014% — and entered a judgment of infringement against Mylan.
Mylan appealed, arguing that the prosecution history and written description showed that the inventors intended the term “0.001%” to mean precisely that concentration, with only minor (approximately 5%) permitted variation — not a broad half-order-of-magnitude range. Mylan’s proposed construction would exclude Mylan’s product, which fell within AstraZeneca’s broader “significant figure” range but not Mylan’s narrow construction.
The Court’s Holding
The Federal Circuit vacated the infringement judgment and adopted Mylan’s narrower construction. The court held that claim construction must be grounded in the intrinsic record — the claim language itself, the patent specification, and the prosecution history. Here, the prosecution history was particularly telling: during prosecution, the inventors had progressively narrowed the claimed concentration range from broad to increasingly precise values, ultimately removing the qualifier “about” (which would have allowed a range) before settling on the exact “0.001%” language. This narrowing history demonstrated that the inventors understood “0.001%” to refer to a specific concentration, not a rounded range.
The written description reinforced this conclusion by consistently describing the invention in terms of precise concentrations. The court affirmed the district court’s separate finding that the asserted claims were not obvious — the prior art taught away from using 0.001% PVP, suggesting that low PVP concentrations were not suitable for aerosol pharmaceuticals. The infringement judgment was vacated, but the nonobviousness finding stood.
Key Takeaways
- The prosecution history is powerful evidence of claim scope — removing qualifying words like “about” or progressively narrowing concentration ranges during prosecution limits a claim to the narrower scope ultimately allowed.
- When a numerical term appears in a claim without qualification, courts will look to the prosecution history and written description to determine whether it should be construed broadly (as a rounded value within one significant figure) or precisely (as a specific value with only minor variation).
- Brand-name pharmaceutical companies asserting broad claim constructions based on “significant figures” reasoning should carefully review their prosecution history, which may undermine arguments for breadth.
- For generic manufacturers (ANDA filers), this decision shows that even if an accused formulation falls within a claimed range under one interpretation, prosecution history can foreclose that broader reading.
Why It Matters
Pharmaceutical patent claims commonly include numerical parameters such as concentrations, pH values, particle sizes, and dosage amounts. Whether such terms are interpreted broadly (using significant figures) or narrowly (as precise values) can determine whether generic drug products infringe. This case is an important reminder that numbers in patent claims do not exist in a vacuum: the prosecution history context — particularly any amendments or cancellations of qualifying language like “about” or “approximately” — controls how courts will interpret those numbers.
For patent applicants, this decision counsels care in prosecution: removing qualifying language has consequences, and progressively narrowing a claim’s numerical range during prosecution will constrain the patent’s scope even if broader language could otherwise support a wider construction. Patent drafters and prosecutors should be deliberate in their choice to include or exclude words like “about” when claiming numerical parameters.