PTAB Affirms Rejection of PK Claims

Pharmaceutical patent lawyers often dream of the perfect patent. One that preludes all generic competition for a drug product long after the compound patent for the molecule has expired. Pharmacokinetic or “PK” patents, which claim the pharmacokinetic profile of a drug, can provide such an opportunity since the generic must be bioequivalent to the innovator’s product to secure FDA approval.  Famous products protected by such patents include Mucinex®, an extended release version of guaifenesin, and Oracea®, a once-daily capsule of doxycycline.  But securing these patents is not always easy as this “chewable tablet” case proves.

Ex parte Tina de Vries and Brian McNamee, 2017 Pat. App. LEXIS 7028 (July 21, 2017) was an appeal to the Patent Trial and Appeals Board (“Board”) from a final rejection of claims for chewable birth control pills.  Claim 1 of the application recited in relevant part:

1. A method of administering ethinyl estradiol … comprising … orally administering a … chewable tablet comprising: (i) 0.5 to 15 ug of ethinyl estradiol; … and (iii) 30% to 90% by weight of … mannitol, and wherein the solid dosage form provides a bioequivalent administration of ethinyl estradiol … compared to a nonchewable solid dosage form comprising ethinyl estradiol … with at least 10 percent less ethinyl estradiol than the nonchewable solid dosage form.

As can be seen, the claim required that the tablet provide a bioequivalent amount of ethinyl estradiol as a non-chewable tablet “with at least 10 percent less ethinyl estradiol.” In other words, the chewable tablet delivers the same amount of ethinyl estradiol as a non-chewable tablet with less ethinyl estradiol.  The claim also required 30-90% mannitol.

For his prima facie case of obviousness, the Examiner cited a reference that disclosed mannitol-based chewable birth control pills. The reference did not disclose any percent ranges for the mannitol, but it did include an example that used 97% mannitol.  The Examiner argued that it would have been obvious to reduce the mannitol percentage to 90%, and thereby come within the claims, because another reference described birth control pills with 75-99% mannitol.

The Examiner acknowledged that the prior art did not disclose the improved bioavailability of mannitol-based chewable tablets, but concluded that this was an inherent property of an obvious formulation.

The Applicant argued that the improved bioavailability of its mannitol-based chewable tablets was unexpected and that this unexpected result proved the patentability of its invention but the Board rejected the argument.  According to the Board, the Applicant has not compared its product to the product of the closest prior art, which contained 97% mannitol, or offered any proof that the 97% mannitol product would not produce a similar result.  As the Board stated:

“While [the primary reference] discloses an amount of 97% outside the claimed range of 90%, Appellants have not explained why increasing amounts of mannitol from 30% to 90% mannitol would possess the claim property, while 97% would not.” 

As this case shows, one way to secure a PK patent is a formulation with unexpected results over the closest prior art.  If the Applicant had shown improved bioavailability versus the 97% mannitol chewable tablet, it probably could have secured this patent.

More importantly, this case shows that securing a broad PK patent requires proof that the PK profile yields unexpected results; not that the formulation yields unexpected pharmacokinetics.  If a formulation yields unexpected results, the claims will be limited to the formulation, just as this application was limited by mannitol.  If a pharmacokinetic profile yields unexpected results, one can potentially secure a patent based solely on pharmacokinetics.