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       United States Court of Appeals
                  FOR THE DISTRICT OF COLUMBIA CIRCUIT




Argued November 8, 2004                   Decided November 30, 2004

                               No. 04-5296

                  MYLAN LABORATORIES, INC., ET AL.,
                          APPELLANTS

                                     v.

                TOMMY G. THOMPSON, SECRETARY,
            UNITED STATES DEPARTMENT OF HEALTH AND
                    HUMAN SERVICES, ET AL.,
                           APPELLEES



          Appeal from the United States District Court
                  for the District of Columbia
                         (No. 04cv01049)



  E. Anthony Figg argued the cause for the appellants.
Thomas C. Goldstein was on brief.
  Paul F. Brinkman, Amy S. Manning and Thomas J.
Parker were on brief for amicus curiae Generic Pharmaceuti-
cal Association in support of appellants.
 Bills of costs must be filed within 14 days after entry of judgment.
The court looks with disfavor upon motions to file bills of costs out
of time.
                              2

  Howard S. Scher, Attorney, United States Department of
Justice, argued the cause for the appellees. Peter D. Keisler,
Assistant Attorney General, Kenneth L. Wainstein, United
States Attorney, Douglas N. Letter, Counsel, United States
Department of Justice, and Alex M. Azar, II, General Coun-
sel, Daniel E. Troy, Chief Counsel, and Eric M. Blumberg,
Deputy Chief Counsel, United States Department of Health
& Human Services, were on brief for federal appellees.
Andrew E. Clark and Karen E. Schifter, Attorneys, United
States Department of Justice, entered appearances.
  Anthony Herman, Peter O. Safir, Carolyn F. Corwin and
Kelly M. Jaske were on brief for appellees Alza Corporation
and Janssen Pharmaceutica, Inc.
  Bruce N. Kuhlik, David E. Korn and Donald O. Beers
were on brief for amicus curiae Pharmaceutical Research
and Manufacturers of America in support of the appellees.
  Gary W. Brown was on brief for amicus curiae Candlel-
ighters Childhood Cancer Foundation National Office in sup-
port of the appellees.
 Before: EDWARDS and HENDERSON, Circuit Judges, and
WILLIAMS, Senior Circuit Judge.
  Opinion for the court filed by Circuit Judge HENDERSON.
   KAREN LECRAFT HENDERSON, Circuit Judge: Appellants
Mylan Laboratories, Inc. Mylan Technologies, Inc. and Mylan
Pharmaceuticals, Inc (Mylan) appeal the district court’s sum-
mary judgment upholding the decision of appellee Food and
Drug Administration (FDA). The FDA decision granted
appellees ALZA Corp. and Janssen Pharmaceutica, Inc, both
subsidiaries of Johnson and Johnson, (collectively, ALZA) a
six-month period of pediatric marketing exclusivity, pursuant
to 21 U.S.C. § 355a, following expiration of the final patent
for ALZA’s brand name transdermal fentanyl system, the
Duragesic patch, which releases fentanyl, a narcotic analgesic,
through the skin to treat chronic pain. Mylan contends the
FDA’s final approval of Mylan’s Abbreviated New Drug
Applications (ANDA) to market a generic version of the
Duragesic patch, granted before the FDA issued the decision
                               3

challenged here, entitled Mylan to market its generic product
immediately upon expiration of the patent pursuant to 21
U.S.C. § 355(j), without regard to pediatric exclusivity. For
the reasons set out below, we affirm the district court’s
judgment upholding the FDA’s decision.


                               I.
   This appeal requires that the court consider three separate
statutory provisions: (1) 21 U.S.C. § 355(j), a provision of the
1984 Hatch–Waxman Amendments to the Federal Food,
Drug, and Cosmetic Act (FDCA), which authorizes a drug
manufacturer to submit an ANDA to the FDA to obtain
approval of a generic version of a previously approved drug;
(2) 21 U.S.C. § 355a, a 1997 amendment to the FDCA, which
authorizes an extra six-month ‘‘pediatric exclusivity’’ period
following expiration of a drug patent for a patent holder that
has satisfactorily conducted pediatric testing of its drug upon
the FDA’s request; and (3) 35 U.S.C. § 271(e)(4), a patent
statute, also enacted in the Hatch–Waxman Amendments,
which sets out the exclusive remedies available in a patent
infringement action. We begin with a summary of these
three provisions.

            A.   Applicable Statutory Provisions
  The ANDA provision, 21 U.S.C. § 355(j), creates an ap-
proval short-cut for applicants seeking to market generic
versions of approved drugs. Under this provision the generic
applicant need not conduct its own clinical trials if the ANDA
certifies that the generic version is bioequivalent to an ap-
proved drug. In addition, the ANDA must include one of
four statutory ‘‘certifications’’ regarding the approved drug’s
patent status:
    (I) that such patent information has not been filed,
    (II) that such patent has expired,
    (III) TTT the date on which such patent will expire, or
                                  4

      (IV) that such patent is invalid or will not be infringed by
           the manufacture, use, or sale of the new drug for
           which the application is submitted; TTTT
21 U.S.C. § 355(j)(2)(A)(vii)(I)-(IV) (paragraphs I-IV). If the
ANDA contains a paragraph IV certification, the applicant
must, within 20 days of the ANDA filing, send a notice to the
patent holder stating it has submitted an ANDA with the
paragraph IV certification and setting out the factual and
legal bases for believing the patent is invalid or will not be
infringed. 21 U.S.C. § 355(j)(2)(B).
   The ANDA provision also establishes the effective date for
approval of the ANDA, depending on the particular certifica-
tion made.
   If the applicant makes a certification under paragraph I or
II, ‘‘the approval may be made effective immediately.’’ 21
U.S.C. § 355(j)(5)(B)(i).
   If the certification is under paragraph III, ‘‘the approval
may be made effective on the date certified under [paragraph
III].’’ 21 U.S.C. § 355(j)(5)(B)(ii).
   If the certification is under paragraph IV, ‘‘the approval
shall be made effective immediately’’ unless the patent holder
files an infringement action in the district court within 45
days of receiving the notice, in which event ‘‘the approval
shall be made effective upon the expiration of the thirty-
month period beginning on the date of the receipt of the
notice,’’ unless the district court rules on the infringement
claim within the 30-month period.                See 21 U.S.C.
§ 355(j)(5)(B)(iii). If the district court issues a ruling during
the 30-month stay period, the ANDA approval date is deter-
mined by the decision of the district court, or the appellate
court if appealed.1
  1 If the district court decides within the stay period that the
patent is invalid or not infringed, ‘‘the approval shall be made
effective on’’ the date of entry of judgment or of a settlement order
or consent decree. 21 U.S.C. § 355(j)(5)(B)(iii)(I). If the district
court decides the patent is infringed and the judgment is not
appealed or is affirmed, ‘‘the approval shall be made effective on the
date specified by the district court in a court order under section
                                    5

   The pediatric exclusivity provision, 21 U.S.C. § 355a, pro-
vides an incentive for a drug patent holder to conduct pedia-
tric studies of a drug which the FDA believes may have
beneficial pediatric use. Under the statute, the FDA must
first request that the drug patent holder conduct pediatric
studies; if the requested studies are satisfactorily completed
and submitted within the FDA-prescribed time frame, the
patent holder is eligible to receive a six-month period of
market exclusivity for the drug beyond the patent expiration
date. 21 U.S.C. § 355a(c). The pediatric exclusivity provi-
sion expressly addresses the effect of a grant of pediatric
exclusivity, depending on the particular certification included
in the ANDA:
     (2)(A) if the drug is the subject of–
           (i) a listed patent for which a certification has been
        submitted under [paragraph II] and for which pedia-
        tric studies were submitted prior to the expiration of
        the patent (including any patent extensions); or
          (ii) a listed patent for which a certification has been
        submitted under [paragraph III],
     the period during which an application may not be ap-
     proved under TTT section 355(j)(5)(B) of this title shall be
     extended by a period of six months after the date the
     patent expires (including any patent extensions); or
       (B) if the drug is the subject of a listed patent for
     which a certification has been submitted under [para-
     graph IV], and in the patent infringement litigation
     resulting from the certification the court determines that
     the patent is valid and would be infringed, the period
     during which an application may not be approved under

271(e)(4)(A).’’ Id. § 355(j)(5)(B)(iii)(II)(bb). In turn, if the infringe-
ment judgment is appealed, ‘‘the approval shall be made effective
on’’ either ‘‘the date on which the court of appeals decides that the
patent is invalid or not infringed’’ or ‘‘the date of a settlement order
or consent decree signed and entered by the court of appeals
stating that the patent that is the subject of the certification is
invalid or not infringed.’’ Id. § 355(j)(5)(B)(iii)(II)(aa).
                                  6

      TTT section 355(j)(5)(B) of this title shall be extended by a
      period of six months after the date the patent expires
      (including any patent extensions).

21 U.S.C. § 355a(c)(2)(A)-(B).2
   Finally, 35 U.S.C. § 271, a patent statute provision, author-
izes the following remedies in a patent infringement action:

      (4) For an act of infringement described in paragraph
      (2)—
          (A) the court shall order the effective date of any
        approval of the drug or veterinary biological product
        involved in the infringement to be a date which is not
        earlier than the date of the expiration of the patent
        which has been infringed,
           (B) injunctive relief may be granted against an in-
        fringer to prevent the commercial manufacture, use,
        offer to sell, or sale within the United States or
        importation into the United States of an approved drug
        or veterinary biological product, and
          (C) damages or other monetary relief may be
        awarded against an infringer only if there has been
        commercial manufacture, use, offer to sell, or sale
        within the United States or importation into the Unit-
        ed States of an approved drug or veterinary biological
        product.
      The remedies prescribed by subparagraphs (A), (B), and
      (C) are the only remedies which may be granted by a
      court for an act of infringement described in paragraph
  2 If the district court in the patent infringement litigation deter-
mines the patent is invalid or will not be infringed, ANDA approval
is effective upon the date of the court order so stating under 21
U.S.C. § 355(j)(5)(B)(iii) and the patent holder is entitled to no
exclusivity thereafter. See, e.g., Mova Pharm. Corp. v. Shalala, 140
F.3d 1060, 1066 (D.C. Cir. 1998).
                               7

    (2), except that a court may award attorney fees under
    section 285.
35 U.S.C. § 271(e)(4).

                    B.   This Proceeding
  Appellee ALZA owned U.S. Patent No. 4,588,580 (’580
patent) for Duragesic. By its terms the ’580 patent expired
on July 23, 2004.
   In July 1999 the FDA wrote ALZA requesting that it
perform pediatric studies of Duragesic pursuant to 21 U.S.C.
§ 355a(c). ALZA submitted the requested studies in Novem-
ber 2002. On January 29, 2003 the FDA granted ALZA a
six-month pediatric exclusivity period.
   Meanwhile, in October 2001 Mylan filed with the FDA an
ANDA to market its generic fentanyl transdermal system
pursuant to 21 U.S.C. § 355(j) with a paragraph IV certifica-
tion that ALZA’s ’580 patent was invalid or would not be
infringed by Mylan’s martketing of its generic product. As
required under 21 U.S.C. § 355(j)(2)(B), on December 6, 2001
Mylan sent ALZA notice of its ANDA application and certifi-
cation which ALZA received on December 10, 2001. On
January 25, 2002, the forty-sixth day after notice was re-
ceived, ALZA filed a patent infringement action against My-
lan in the United States District Court for the District of
Vermont. Because the action was not brought within the
statutory 45-day window following notice receipt, there was
no automatic 30-month stay and, under 21 U.S.C.
§ 355(j)(5)(B)(iii), Mylan’s ANDA was to ‘‘be made effective
immediately.’’ Accordingly, on November 21, 2003, the FDA
granted final approval of Mylan’s ANDA.
   On March 24, 2004 the Vermont District Court issued a
decision holding that ‘‘[t]he ’580 patent is not invalid’’ and
‘‘Mylan’s ANDA filing for a generic version of Duragesic b
infringe[s] TTT the ’580 patent.’’ ALZA v. Mylan, 310 F.
Supp. 2d 610, 637 (D. Vt. 2004). The court therefore enjoined
Mylan from ‘‘making, using, offering to sell, selling within the
United States or importing into the United States’’ its generic
                                  8

fentanyl transdermal system. 310 F. Supp. 2d at 637. Re-
garding Mylan’s ANDA approval, the court stated simply that
‘‘the effective date of any approval of Mylan’s ANDA product
shall be no earlier than the date of expiration of the ’580
patent family.’’ Id. Mylan appealed the decision to the
Federal Circuit where it remains pending.
   In the meantime, both Mylan and ALZA sought a determi-
nation from the FDA on whether Mylan could lawfully mar-
ket its generic fentanyl transdermal system when the ’580
patent expired or whether Mylan was required to wait until
the six-month pediatric exclusivity period expired. In two
letters dated June 22, 2004, the FDA issued its administrative
decision.
   In the first letter (Letter 1), addressed to counsel for both
parties, the FDA concluded that ‘‘ALZA’s pediatric exclusivi-
ty for fentanyl will attach, and thus delay effective approval of
Mylan’s ANDA,’’ so that ‘‘[u]nless Mylan were to win its
patent case on appeal, Mylan’s ANDA would be eligible for
final effective approval no earlier than six months after
the ’580 patent expires on July 23, 2004.’’ Letter 1 at 11.
The FDA rested its decision on two key determinations.
   First, the FDA concluded that the Vermont district court’s
order that ‘‘the effective date of any approval of Mylan’s
ANDA product shall be no earlier than the date of expiration
of the ’580 patent family,’’ 310 F. Supp. 2d at 637, trans-
formed Mylan’s ANDA approval into ‘‘an approval with a
delayed effective date,’’ which ‘‘is a tentative approval that
cannot be made effective until FDA issues a letter granting
final effective approval.’’ Letter 1 at 11 (citing 21 C.F.R.
§ 314.107(b)(3)(v);3 Barr Labs. v. Thompson, 238 F. Supp. 2d
236, 245-50 (D.D.C. 2002)).
  3   This regulation provides:
      In order for an approval to be made effective under paragraph
      (b)(3) of this section, the applicant must receive an approval
      letter from the agency indicating that the application has
      received final approval. Tentative approval of an application
                                  9

   Second, the FDA concluded that, when ALZA’s patent
expired, Mylan’s paragraph IV certification would no longer
be accurate and Mylan would be required to amend it or, ‘‘[i]f
Mylan refuses to amend its application to change its certifica-
tion after the patent expires, FDA can treat that certification
as automatically amended to contain a paragraph II certifica-
tion (because there is no other proper certification upon
expiry).’’ Letter 1 at 12 (citing Ranbaxy Labs. v. FDA, 307
F. Supp. 2d 15, 19, 21 (D.D.C. 2004), aff’d, 96 Fed. App. 1
(D.C. Cir 2004)). Then, once Mylan’s certification converted
to paragraph II, ‘‘pediatric exclusivity attaches under
355a(c)(2)(A)(i),’’ Letter 1 at 12 (citing Ranbaxy, 307 F. Supp.
2d at 20, 21), so that ‘‘ ‘the period during which an [ANDA]
may not be approved TTT shall be extended by a period of six
months after the date the patent expires,’ ’’id. (quoting 21
U.S.C. § 355a(c)(2)(A)(i)).
   In the second letter (Letter 2), addressed to Mylan only,
the FDA informed Mylan that, ‘‘in light of [the Vermont
district court’s] decision, the Agency hereby rescinds the final
approval of ANDA 76–258 issued on November 21, 2003, and
regards ANDA 76–258 as tentatively approved.’’ Letter 2 at
1. The letter again noted that, after the Vermont district
court’s order, Mylan’s ANDA approval had ‘‘a delayed effec-
tive date,’’ which, by FDA regulation, constitutes ‘‘tentative,’’
rather than ‘‘final,’’ approval.       Id. (citing 21 C.F.R.
               4
§ 314.105(a)). Accordingly, the FDA informed Mylan: ‘‘Fi-
nal Approval cannot be granted earlier than the date of a
court decision finding the patents invalid, not infringed or
unenforceable, or the expiration date of the patent and any
period of pediatric exclusivity granted to the NDA holder.’’

      does not constitute ‘‘approval’’ of an application and cannot,
      absent a final approval letter from the agency, result in an
      effective approval under paragraph (b)(3) of this section.
  4This regulation provides: ‘‘An approval becomes effective on the
date of the issuance of the approval letter, except with regard to an
approval under section 505(b)(2) of the act with a delayed effective
date. An approval with a delayed effective date is tentative and
does not become final until the effective date.’’
                               10

Id. at 1-2 & n.2 (noting that Mylan’s ANDA was ‘‘subject to
ALZA’s pediatric exclusivity for fentanyl transdermal sys-
tem’’).
   On June 24, 2000 Mylan filed this action in the district
court seeking a determination that the FDA’s ‘‘revocation’’ of
Mylan’s final ANDA approval was unlawful and an injunction
prohibiting the FDA ‘‘from revoking the final approval of
Mylan’s ANDA and from applying [ALZA’s] pediatric exclu-
sivity to Mylan’s ANDA.’’ Mylan v. Thompson, 332 F. Supp.
2d 106, 114 (D.C.C. 2004). In a decision filed August 17, 2004
the district court granted summary judgment in the FDA’s
favor, concluding that the agency ‘‘did not improperly revoke
or reclassify its final approval of Mylan’s ANDA for a generic
version of a fentanyl transdermal system to a tentative ap-
proval and did not improperly apply ALZA pediatric exclusiv-
ity to Mylan’s ANDA.’’ 332 F. Supp. 2d at 124. Mylan
appealed the district court’s summary judgment.

                                II.
   ‘‘The court reviews the district court’s summary judgment
decision de novo and ‘we may affirm only if ‘‘there is no
genuine issue as to any material fact [and] the moving party
is entitled to judgment as a matter of law.’’ ’ ’’ Trans Union
LLC v. Fed. Trade Comm’n, 295 F.3d 42, 48 (D.C. Cir. 2002)
(quoting Gilvin v. Fire, 259 F.3d 749, 756 (D.C. Cir 2001)
(quoting Anderson v. Liberty Lobby, Inc., 477 U.S. 242, 250
(1986) (quoting Fed. R. Civ. P. 56(C)))). We review the
FDA’s decision under the Administrative Procedure Act, 5
U.S.C. § 706(2)(A). Serono Labs. v. Shalala, 158 F.3d 1313,
1327 (D.C. Cir. 1998) (citing Troy Corp. v. Browner, 120 F.3d
277, 283 (D.C. Cir. 1997); Schering Corp v. FDA, 51 F.3d 390,
399 (3d Cir. 1995)). Accordingly, we must uphold the FDA’s
decision unless it is ‘‘arbitrary, capricious, an abuse of discre-
tion, or otherwise not in accordance with law.’’ 5 U.S.C.
§ 706(2). We conclude that the FDA’s decision was none of
these.
  At issue is the FDA’s application of the statutory provisions
summarized above. ‘‘Ordinarily we review an agency’s inter-
                                11

pretation of a statute it is charged with implementing under
the familiar and deferential two-part framework of Chevron
U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467
U.S. 837, 104 S.Ct. 2778, 81 L.Ed.2d 694 (1984).’’ Pharm.
Research & Mfrs. of Am. v. Thompson, 362 F.3d 817, 821
(D.C. Cir. 2004). Mylan contends, however, that only minimal
deference is owed to the FDA’s interpretation of the FDCA
because it was expressed in letters to the parties and ‘‘is not
embodied in any regulation, much less a regulation that was
subject to notice and comment rulemaking.’’ Appellants’ Br.
at 19-20. The FDA’s letter decisions, Mylan maintains, are
‘‘analogous to ‘opinion letters,’ ’’ id. at 20 (quoting Skidmore
v. Swift & Co., 323 U.S. 134, 140 (1944)), and therefore ‘‘do
not warrant Chevron-style deference’’ but are entitled only
‘‘ ‘ ‘‘to respect’’ ’ ’’ and even then ‘‘ ‘only to the extent that
those interpretations have the power ‘‘to persuade,’’ ’ ’’ Chris-
tensen v. Harris County, 529 U.S. 576, 587 (2000) (quoting
Skidmore, 323 U.S. at 140; other citations omitted)). We are
not persuaded by Mylan’s argument and conclude, as did the
district court, that the FDA’s decision is entitled to Chevron
deference.5
  ‘‘ ‘[T]he want of’ notice and comment ‘does not decide the
case’ ’’ against Chevron deference. Barnhart v. Walton, 535
U.S. 212, 222 (2002) (quoting United States v. Mead Corp.,
533 U.S. 218, 230-31 (2001)). ‘‘Indeed, Mead pointed to
instances in which the Court has applied Chevron deference
to agency interpretations that did not emerge out of notice-
and-comment rulemaking,’’ Id. (citing United States v. Mead
Corp., 533 U.S. at 230-31 (citing NationsBank of N. C., N.A.
v. Variable Annuity Life Ins. Co., 513 U.S. 251, 256-57
  5    Mylan also asserts, correctly, that the court owes no defer-
ence to the FDA’s interpretation of 35 U.S.C. § 271(e)(4)(A), a
patent statute provision which the FDA is not charged with admin-
istering, see Scheduled Airlines Traffic Offices, Inc. v. Dep’t of
Defense, 87 F.3d 1356, 1361 (D.C. Cir. 1996); or of the decision of
the Vermont district court, see American Bioscience v. Thompson,
269 F.3d 1077, 1085 (D.C. Cir. 2001). Neither the statute nor the
court decision, however, presented any ambiguity for the FDA to
interpret.
                               12

(1995))). ‘‘[W]hether a court should give such deference
depends in significant part upon the interpretive method used
and the nature of the question at issue.’’ Id. (citing Mead,
533 U.S. at 229-31). In Barnhardt the Court concluded that
‘‘the interstitial nature of the legal question, the related
expertise of the Agency, the importance of the question to
administration of the statute, the complexity of that adminis-
tration, and the careful consideration the Agency has given
the question over a long period of time all indicate that
Chevron provides the appropriate legal lens through which to
view the legality of the Agency interpretation here at issue.’’
Id. We reach the same conclusion here.
  There is no denying the complexity of the statutory regime
under which the FDA operates, the FDA’s expertise or the
careful craft of the scheme it devised to reconcile the various
statutory provisions. Further, the FDA’s decision made no
great legal leap but relied in large part on its previous
determination of the same or similar issues and on its own
regulations. See Letter 1 at 11-12 (citing 21 C.F.R.
§ 314.107(b)(3)(v), Barr and Ranbaxy); Letter 2 at 1 (citing
21 C.F.R. § 314.105(a)). We therefore accord Chevron defer-
ence to the FDA’s letter decision here, as we have previously
done on at least one other occasion. See Abbott Labs. v.
Young, 920 F.2d 984, 986-89 (D.C. Cir. 1990), cert. denied, 502
U.S. 819 (1991) (reviewing under Chevron letter decision
construing term ‘‘active ingredient’’ in ANDA provision, 21
U.S.C. § 355(j)(4)(D)(i), (v)); id. at 992–96 (Edwards, J.,
dissenting) (applying Chevron); see also Barr Labs. v.
Thompson, 238 F. Supp. 2d 236, 245-50 (D.D.C. 2002) (apply-
ing Chevron to FDA letter ruling).6
   ‘‘Under the Chevron framework, ‘[i]f TTT ‘‘Congress has
directly spoken to the precise question at issue,’’ we must give
effect to Congress’s ‘‘unambiguously expressed intent’’ ’ but
  6 Even were the FDA’s decision subject only to Skidmore defer-
ence, the result would likely be the same. See Ranbaxy Labs. v.
FDA, 96 Fed. App. 1, 1 (D.C. Cir. 2004) (‘‘Regardless whether the
[FDA’s] decision is reviewed under [Skidmore or Chevron], the
district court properly affirmed the FDA’s determinationTTTT’’).
                               13

‘[i]f ‘‘the statute is silent or ambiguous with respect to the
specific issue,’’ we ask whether the agency’s position rests on
a ‘‘permissible construction of the statute.’’ ’ ’’ Pharm. Re-
search & Mfrs., 362 F.3d at 823–24 (quoting Beverly Health &
Rehab. Servs. v. NLRB, 317 F.3d 316, 321 (D.C. Cir. 2003)
(quoting Chevron, 467 U.S. at 842–43). In applying the
FDCA provisions to the particular facts here, the FDA found
two ambiguities.
   First, application of the various statutory provisions results
in conflicting effective dates for Mylan’s ANDA. The patent
infringement remedy statute, 35 U.S.C. § 271(e)(4)(A), directs
that the court deciding the infringement action ‘‘shall order
the effective date of any approval of the drug or veterinary
biological product involved in the infringement to be a date
which is not earlier than the date of the expiration of the
patent which has been infringed,’’ which is precisely what the
Vermont district court did here, directing that ‘‘the effective
date of any approval of Mylan’s ANDA product shall be no
earlier than the date of expiration of the ’580 patent family,’’
310 F. Supp. 2d at 637; yet under 21 U.S.C. § 355(j)(5)(B)(iii),
approval of the paragraph IV ANDA was to ‘‘be made
effective immediately’’ after the 45-day window closed without
an infringement action filed by the patent holder, so that the
FDA was required to (and did) grant final approval of My-
lan’s ANDA, immediately effective, notwithstanding the pend-
ing infringement action. As a result, at the time of the FDA
letter decision, Mylan’s ANDA was subject to two conflicting
approval effective dates: the date of the FDA’s approval
decision (November 21, 2003) and, pursuant to the Vermont
district court’s order, a date ‘‘no earlier than the date of
expiration of the ’580 patent family’’ (i.e., July 23, 2004).
   Second, after the Vermont district court’s finding of patent
validity, Mylan’s paragraph IV ANDA certification was at
variance with the legal reality. Because the ’580 patent was
then valid and infringed as a matter of law, ANDA’s certifica-
tion that the ’580 patent ‘‘is invalid or will not be infringed by
the manufacture, use, or sale of the new drug for which the
application is submitted’’ was no longer accurate. Further,
                                14

section 355a(c)(2), which governs the consequences for pedia-
tric exclusivity under each of the alternative patent certifica-
tions, provided no mechanism to resolve this discrepancy
because, at least as construed in the administrative proceed-
ing, this section applies to a paragraph IV certification only if
an infringement action has been filed within the 45-day
window so as to trigger the 30–month stay period.7 Because
the infringement action here was filed outside the 45-day
window, the FDA was left with a statutory gap to fill.
  In deciding the exclusivity issue submitted by Mylan and
ALZA, the FDA was called upon to construe the statutes so
as to resolve these two conflicts. We conclude the FDA did
so in a way that reflects a permissible construction of the
applicable FDCA provisions and therefore satisfies Chevron.
See Western Coal Traffic League v. Surface Transp. Bd., 216
F.3d 1168, 1173 (D.C. Cir. 2000) (reviewing under Chevron
agency resolution of ‘‘unanticipated conflict’’ arising from
application of statute).

A.    Conversion of Approval from ‘‘Final’’ to ‘‘Tentative’’
    First, the FDA concluded that, as a consequence of the
Vermont district court’s determination under 35 U.S.C.
§ 271(e)(4)(A) that ‘‘the effective date of any approval of
Mylan’s ANDA product shall be no earlier than the date of
expiration of the ’580 patent family,’’ the FDA’s approval of
Mylan’s ANDA was no longer ‘‘immediately effective’’—its
effective date had changed, as the Congress had contemplat-
ed it would under such circumstances when it enacted 35
U.S.C. § 271. See H.R. Rep. No. 98-857, pt. 1, at 46 (1984)
(‘‘In the case where an ANDA had been approved, the order
would mandate a change in the effective date.’’). The FDA
  7 On appeal the appellees argue alternatively that section
355a(c)(2)(B) can be read to cover the situation when the action is
filed after the 45-day window as well as before (obviating the need
for certification conversion). This may well be a permissible con-
struction of the provision but it is not the reading the FDA applied
during the administrative proceeding nor the one before us on
review of the FDA’s decision.
                                 15

next determined, logically enough, that the effective date was
then ‘‘delayed’’ and therefore ‘‘tentative,’’ rather than ‘‘imme-
diate’’ and ‘‘final,’’ under the FDA’s own regulation which
provides that ‘‘[a]n approval with a delayed effective date is
tentative and does not become final until the effective date.’’
21 C.F.R. § 314.105(a); see Barr Labs. v. Thompson, 238 F.
Supp. 2d 236, 245-50 (D.D.C. 2002) (upholding FDA determi-
nation under 21 C.F.R. § 314.105(a) that ANDA approval
before patent expiration was tentative, not final).
   Mylan contends the FDA lacked authority to revoke My-
lan’s final ANDA approval granted on November 21, 2003
because its authority to revoke a final approval is limited to
those specific circumstances set out in 21 U.S.C. § 355(e),
none of which exists here. Mylan’s characterization of sec-
tion 355(e) is off the mark. As the FDA indicates in its
decision, Letter 1 at 12 n.10, section 355(e) simply sets out
specific, not necessarily exclusive, circumstances under which
the FDA must withdraw any ANDA approval (whether final
or otherwise) after notice and hearing. But the provision
does not prohibit the FDA from withdrawing approval under
other circumstances—or, more precisely, does not prohibit
the FDA from changing a final into a tentative approval
under circumstances different from those named in section
355(e).8 Moreover, the patent remedy statute directs that
upon a finding of infringement the district court establish a
new effective date for approval which is ‘‘not earlier than the
date of the expiration of the patent which has been infringed.’’
35 U.S.C. § 271(e)(4)(A), and the FDA was bound under the
district court’s order to treat the status of Mylan’s ANDA
under the FDCA ‘‘the same as that of other ANDAs blocked
from final approval by patent or exclusivity rights.’’ Letter 1
at 12 n.10.
  8 We are skeptical whether the parties properly characterize the
FDA’s action as ‘‘withdrawal’’ or ‘‘revocation’’ of approval. It seems
to us that Mylan’s ANDA approval was never in fact ‘‘withdrawn’’
or ‘‘revoked’’ but remained continuously in effect based on the
FDA’s review of the ANDA described in the November 21, 2003
final approval letter. The approval merely underwent a change of
                                16

   Mylan also claims the approval conversion is ‘‘contrary to
past Agency practice.’’ Appellants’ Br. 43 (citing Mead John-
son Pharm. Group v. Bowen, 838 F.2d 1332, 1334 (D.C. Cir.
1988), and Unimed, Inc. v. Quigg, 888 F.2d 826, 827 (Fed.
Cir. 1989)). Each cited case, however, involved not an ANDA
but a New Drug Application, a different animal entirely
because the latter is generally not subject to a delayed
effective date, and each application was subject to an approval
letter authorizing immediate marketing without any delayed
effective date. See Mead Johnson, 838 F.2d at 1336 (noting
applicant could have marketed its product on day of approval
by filing required supplemental labeling); Unimed, 888 F.2d
at 828 (FDA letter noting product could not be marketed
until it was ‘‘rescheduled’’ by DEA simply ‘‘reminded Unimed
that DEA rescheduling was necessary before the drug could
be marketed’’ and ‘‘was not a condition on FDA approval’’)
(emphasis original).9

             B.   Conversion of Paragraph IV to
                  Paragraph II Certification
  The FDA next addressed the problem of Mylan’s inaccu-
rate ANDA certification and resolved it relying on Ranbaxy
Labs. v. FDA, 307 F. Supp. 2d 15 (D.D.C. 2004), aff’d, 96 Fed.
App. 1 (D.C. Cir 2004). The FDA concluded that under
Ranbaxy when the ’580 patent expired, Mylan’s paragraph IV
certification would convert to a paragraph II certification and
ALZA would be entitled to pediatric exclusivity for six
months following the expiration. The FDA reasoned that

status or classification from final to tentative after the Vermont
district court delayed its effective date.
  9 Nor do we see any force in Mylan’s citation to the FDA’s 1994
rulemaking, in which the FDA declined to extend by rule the
statutory 45-day window. Appellants’ Br. at 42 (quoting 59 Fed.
Reg. at 50,353). The FDA simply explained there that if the
window were to be extended (which it was not), the FDA would
retain authority during the extension to grant final effective ANDA
approval, notwithstanding the patent holder might subsequently file
a successful infringement action.
                               17

once the certification became inaccurate, Mylan was under a
duty to amend its ANDA to change the certification to
paragraph II, see 21 C.F.R. § 314.94(a)(12)(viii)(C)(i) (provid-
ing ‘‘an applicant shall amend a submitted certification if, at
any time before the effective date of the approval of the
application, the applicant learns that the submitted certifica-
tion is no longer accurate’’); and if Mylan failed to do so, the
FDA could ‘‘treat that certification as automatically amended
to contain a paragraph II certification.’’ Letter 1 at 12.
Once the certification changed to paragraph II—whether de
facto or de jure—pediatric exclusivity attached under 21
U.S.C. § 355a(c)(2)(A)(i) (‘‘[I]f the drug is the subject of– TTT
a listed patent for which a certification has been submitted
under [paragraph II] and for which pediatric studies were
submitted prior to the expiration of the patent; TTT the
period during which an application may not be approved
under TTT section 355(j)(5)(B) of this title shall be extended
by a period of six months after the date the patent expires.’’).
We find the FDA’s application of the statutory provisions
both reasonable and supported by Ranbaxy.
   In Ranbaxy the FDA also converted an ANDA classifica-
tion from a paragraph IV to a paragraph II certification
under similar circumstances. The patent holder in Ranbaxy
filed an infringement action within forty-five days after re-
ceiving the required paragraph IV certification notice. Upon
learning the district court would be unable to decide the case
before the patent expiration date, the parties signed a stipula-
tion to dismiss the action as of the expiration date. The day
before expiration, the FDA informed the ANDA applicant
that its ANDA would be subject to a six-month pediatric
exclusivity period for the patented drug. There, as here, 21
U.S.C. § 355a(c)(2)(B) did not apply (there, because there was
no finding of a valid patent or infringement) and the FDA
concluded that upon the patent expiry the paragraph IV
certification converted to a paragraph II certification and
pediatric     exclusivity   attached    under      21    U.S.C.
§ 355a(c)(2)(A)(i). The district court agreed with the FDA’s
statutory construction and on appeal we concluded:
                                18

    [T]he district court properly affirmed the FDA’s determi-
    nation that, under the Federal Food, Drug, and Cosmetic
    Act, 21 U.S.C. § 301, et seq., final approval of Ranbaxy’s
    Abbreviated New Drug Applications (‘‘ANDAs’’) did not
    automatically occur upon the dismissal of the underlying
    patent litigation, the expiration of the patent, and the
    termination of the thirty-month statutory stay. The
    district court also properly affirmed the FDA’s conclu-
    sion that, upon the expiration of Pfizer’s patent on Janu-
    ary 29, 2004, Ranbaxy’s ‘‘Paragraph IV’’ certifications
    became invalid, and the applicable pediatric exclusivity
    provision became 21 U.S.C. § 355a(c)(2)(A), the provision
    pertaining to ‘‘Paragraph II’’ certifications. Id. Under
    that provision, approval of Ranbaxy’s ANDAs is delayed
    six monthsTTTT See 21 U.S.C. § 355a(c)(2)(A).
96 Fed. App. at 1. For the same reasons, the district court
here acted properly in upholding the FDA’s certification
conversion.
    Mylan contends that one of the FDA’s own regulations
weighs against this rationale, namely, 21 C.F.R.
§ 314.94(a)(12)(viii)(A), which requires that an ANDA appli-
cant amend its application to recertify under paragraph III
(‘‘that the patent will expire on a particular date’’) if a finding
of validity/infringement is made in a lawsuit that has been
filed within the statutory 45-day window. Mylan asserts the
‘‘necessary implication’’ of this language is that ‘‘if the appli-
cant is not sued within the forty-five-day-period, 21 U.S.C.
§ 355(j)(5)(B)(iii) requires that approval of an ANDA shall be
‘effective immediately’ and certifications are no longer rele-
vant.’’ Appellants’ Br. at 42. Mylan reads too much into the
regulation. That the FDA has expressly required recertifica-
tion when an action is filed within the 45-day window does not
‘‘necessarily’’ mean an applicant need not amend its applica-
tion to change the patent certification to reflect changed
circumstances if the action is not filed within the window. To
the extent that the cited regulation is relevant here, it sup-
ports the FDA’s rationale in requiring a generic drug appli-
                                  19

cant to amend its ANDA to include an accurate certification.10
   Mylan also contends the FDA’s construction ‘‘would read
[section 355a(c)(2)(B)] entirely out of the statute’’ because, if
it ‘‘does not govern the availability of pediatric exclusivity in
cases like this one involving Paragraph IV certifications in
which infringement is found, the statute serves no purpose at
all.’’ Appellants’ Br. at 22-23. Not so. Under the FDA’s
interpretation, section 355a(c)(2)(B) applies when—and only
when—all three of its express conditions are met: ‘‘a certifi-
cation has been submitted under [paragraph IV],’’ there is
‘‘patent infringement litigation resulting from the certifica-
tion’’ and in the litigation ‘‘the court determines that the
patent is valid and would be infringed.’’ It is only because
one of these requirements was missing in Ranbaxy (a valid
patent finding) and in this case (an infringement action filed
within the 45-day window) that the FDA, prevented from
applying its reading of section 355a(c)(2)(B), was required to
fill the statutory gap by deeming the patent certification
changed.

                             * * *
   We affirm the district court’s judgment because the FDA’s
decision reasonably resolves the ambiguity in applying the
relevant statutes to a factual situation not fully foreseen or
provided for by the Congress when it enacted the statutes or
the FDA when it promulgated regulations. The Vermont
district court’s finding of patent validity and consequent
injunction changed the factual and legal landscape and the
agency’s response to the court’s decision is both reasonable
and consistent with the statutory language. The FDA’s
  10 The FDA might well have concluded that in this situation too,
as ALZA suggested in the administrative proceeding, see Letter 1
at 11, the paragraph IV certification should have changed to a
paragraph III certification immediately upon the district court’s
finding of validity/infringement, consistent with the directive of 21
C.F.R. § 314.94(a)(12)(viii)(C)(1)(i) that ‘‘an applicant shall amend a
submitted certification if, at any time before the effective date of
the approval of the application, the applicant learns that the submit-
ted certification is no longer accurate.’’
                                 20

solution effects the policies of both the generic ANDA provi-
sion, by eliminating the need for Mylan to conduct clinical
trials of its generic product, and the pediatric exclusivity
provision, by granting ALZA a six-month exclusivity period in
return for the pediatric studies it performed, the adequacy of
which Mylan does not dispute. At the same time, it main-
tains the incentive under 21 U.S.C. § 355(j)(5)(B)(iii) for a
patent holder to promptly file an infringement action when its
patent is challenged because, if the patent holder fails to do
so within forty-five days, it will lose the benefit of the 30-
month stay period and possibly, for a time, market exclusivity
it should rightfully enjoy.11
                                                        So ordered.
  11 In a case such as this, for example, if the district court found

the patent invalid, without the 30–month stay the ANDA applicant
would obtain immediate approval under the court’s decision to
market its generic product notwithstanding the patent holder might
subsequently successfully appeal the district court’s decision.
