United States Patent 5,547,948: Claim Scope, Expiration, Orange Book Relevance, and Generic Entry Risk

U.S. Patent No. 5,547,948 protects a specific oral hormone-replacement tablet architecture: conjugated estrogens in a compressed tablet core and a sugar coating containing a hormonal steroid plus microcrystalline cellulose. Claims 3, 4, 5, and 6 narrow the protection to medroxyprogesterone acetate, sucrose, and defined dosage ranges.

The patent is directed to the formulation and physical arrangement of the product, not to conjugated estrogens or medroxyprogesterone acetate as chemical entities. Its practical relevance was tied to combination products such as Prempro. The patent has reached the end of its enforceable term, eliminating current patent-based generic entry risk from this patent.

What does U.S. Patent 5,547,948 protect?

The patent protects a two-part tablet structure with the active ingredients distributed between the tablet core and the coating.

Claim	Core	Sugar coating	Additional limitation
1	Conjugated estrogens	Hormonal steroid and microcrystalline cellulose	Microcrystalline cellulose controls steroid release
2	0.1-5.0 mg conjugated estrogens	1.0-50 mg hormonal steroid	Depends on claim 1
3	0.3-2.5 mg conjugated estrogens	1.5-30 mg medroxyprogesterone acetate	Depends on claim 1
4	Conjugated estrogens	Medroxyprogesterone acetate, sucrose, and microcrystalline cellulose	Steroid is specifically MPA
5	0.1-5.0 mg conjugated estrogens	1-50 mg medroxyprogesterone acetate	Depends on claim 4
6	0.3-2.5 mg conjugated estrogens	2.5-30 mg medroxyprogesterone acetate	Depends on claim 4

Claim 4 contains apparent transcription errors in the supplied text. “Asteroid release rate controlling amount” should be read in context as “a steroid release rate controlling amount,” and the phrase “incorporates with the sugar sucrose” appears to mean that the coating incorporates sucrose, medroxyprogesterone acetate, and microcrystalline cellulose.

The commercial value of the patent came from placing conjugated estrogens and medroxyprogesterone acetate in different physical portions of the same tablet. That arrangement could permit separate control of the release behavior of the steroid component.

How should the independent claims be construed?

Claim 1: broadest formulation claim

Claim 1 requires all of the following:

A compressed tablet.
A tablet core containing conjugated estrogens.
A sugar coating.
A hormonal steroid in the sugar coating.
Microcrystalline cellulose in the sugar coating.
An amount of microcrystalline cellulose that controls the steroid release rate.

The claim is broader than the MPA-specific claims because “hormonal steroid” is not limited expressly to medroxyprogesterone acetate. It could potentially encompass other steroid hormones if they are placed in the sugar coating with release-rate-controlling microcrystalline cellulose.

The claim is narrower than a general conjugated-estrogen/progestin combination claim. It does not cover every tablet containing conjugated estrogens and a steroid. The claimed distribution of ingredients between the core and coating is central.

Claim 4: narrower MPA and sucrose claim

Claim 4 adds two material limitations:

The hormonal steroid is medroxyprogesterone acetate.
The sugar coating incorporates sucrose.

A product containing conjugated estrogens and MPA in a conventional homogeneous tablet core would not fall within the literal scope of claim 4. The claim requires MPA in the sugar coating, not merely somewhere in the finished dosage form.

What dosage strengths are covered by the patent?

Claims 2, 3, 5, and 6 define dosage ranges for the two active ingredients.

The most commercially relevant narrowed claims are claims 3 and 6. They cover conjugated-estrogen amounts from 0.3 to 2.5 mg and MPA amounts within either 1.5-30 mg or 2.5-30 mg, depending on the claim.

Common conjugated estrogen/MPA strengths associated with Prempro-type products fall within these numerical ranges, including:

Conjugated estrogens	MPA	Relevance
0.3 mg	1.5 mg	Within claim 3; outside claim 6’s lower MPA boundary
0.45 mg	1.5 mg	Within claim 3
0.625 mg	2.5 mg	Within claims 3 and 6
0.625 mg	5 mg	Within claims 3 and 6
0.9 mg	1.5 mg	Within claim 3
1.25 mg	5 mg	Within claims 3 and 6

Dosage strength alone does not establish infringement. The accused product would also need the claimed tablet-core and sugar-coating arrangement.

What formulations are protected by U.S. Patent 5,547,948?

The patent protects a coated tablet in which the formulation is spatially divided:

Conjugated estrogens are in the compressed core.
MPA or another hormonal steroid is in the sugar coating.
Microcrystalline cellulose is in the coating.
In claims 4-6, sucrose is also in the coating.
The microcrystalline cellulose must have a release-rate-control function.

This structure distinguishes the patent from several alternative formulations.

Formulations likely outside the literal claims

The following designs generally avoid at least one express claim element:

Alternative design	Missing claim element
Both actives blended into the tablet core	Steroid is not in the sugar coating
MPA in a film coat rather than a sugar coat	No claimed sugar coating
MPA in a capsule	Not a compressed tablet
Conjugated estrogens and MPA supplied as separate tablets	No single claimed tablet
MPA in an immediate-release coating without MCC	No release-rate-controlling MCC
A transdermal estrogen plus oral progestin	No claimed tablet structure
Estradiol plus progesterone	No conjugated estrogens and no MPA, depending on the claim
Conjugated estrogens plus bazedoxifene	No MPA
Conjugated estrogens plus norethindrone acetate	No MPA

The “sugar coating” limitation is potentially important. A formulation using a conventional polymeric film coating may avoid literal infringement, although infringement analysis would depend on the actual composition and prosecution history.

When did U.S. Patent 5,547,948 expire?

U.S. Patent 5,547,948 issued on August 20, 1996. Its enforceable term ended no later than the applicable statutory term for the patent family. Public patent records identify the patent as expired, and the patent cannot presently block an ANDA, 505(b)(2) application, or commercial launch on a forward-looking basis.

The patent’s expiration means:

No current Paragraph IV challenge is needed to neutralize this patent.
FDA approval of a generic product is not blocked by this patent.
A generic manufacturer does not need to wait for the patent term to end.
The patent cannot support a new patent-infringement action based solely on post-expiration manufacture or sale.

Patent expiration does not eliminate possible regulatory, trademark, trade-secret, formulation, or separate patent issues.

What was the Orange Book status of the patent?

The patent was associated with the Prempro product family, which contained conjugated estrogens and medroxyprogesterone acetate. Prempro was approved by FDA as a prescription hormone-replacement product marketed by Wyeth, later part of Pfizer.

The Orange Book relevance was formulation-specific. A listing for a patent of this type would notify an ANDA applicant that FDA considered the patent relevant to the reference product. It would not mean that all conjugated-estrogen products, all MPA products, or all estrogen/progestin combinations were covered.

An ANDA applicant historically could address such a listing through:

Paragraph I certification, if the patent information was no longer applicable;
Paragraph II certification, if the patent had expired;
Paragraph III certification, accepting approval after expiration; or
Paragraph IV certification, asserting that the patent was invalid, unenforceable, or not infringed.

Because U.S. Patent 5,547,948 is expired, the relevant current certification posture is Paragraph II or Paragraph III depending on the applicant’s regulatory filing date and the status of other listed patents.

Were there Paragraph IV challenges or generic litigation?

A Paragraph IV certification would have been commercially relevant before expiration if an ANDA product reproduced the claimed coated-tablet architecture. The principal litigation risk would have involved whether the generic product placed MPA in a sugar coating containing microcrystalline cellulose that controlled release.

The critical infringement questions would have included:

Whether the generic had a true sugar coating rather than a polymeric film coating.
Whether MPA was located in the coating rather than the tablet core.
Whether the microcrystalline cellulose controlled MPA release.
Whether the active-ingredient amounts fell within the asserted dependent claims.
Whether the patent’s claims were invalid for anticipation or obviousness.
Whether the patent had enforceable Orange Book status when the ANDA was filed.

The supplied record does not establish a particular district-court case, settlement agreement, or launch-at-risk decision tied specifically to Patent 5,547,948. The patent’s expiration makes historical litigation more relevant than current litigation.

How strong was the patent estate for Prempro?

The patent was technically narrow but commercially useful against a matching product design.

Strength factor	Assessment
Chemical composition protection	Low; the patent does not claim conjugated estrogens or MPA as compounds
Dosage-form protection	High for the claimed coated-tablet architecture
Design-around risk	Moderate to high
Protection for separate tablets	None
Protection for transdermal products	None
Protection for other progestins	Limited to claim 1’s broader steroid language
Protection after expiration	None
Manufacturing barrier	Moderate; the coating process and release profile could create development hurdles
Regulatory barrier	Dependent on FDA-listed patents and reference-product requirements

The claims are strongest when an accused product copies the same physical arrangement. They are weaker against products using different coating systems, different active-ingredient placement, or different delivery technologies.

How does Patent 5,547,948 compare with competing hormone-replacement products?

The patent does not cover the principal competing hormone-replacement architectures shown below.

Product category	Estrogen	Progestin or other agent	Likely relationship to Patent 5,547,948
Prempro-type product	Conjugated estrogens	MPA	Within the commercial field targeted by the patent
Premarin	Conjugated estrogens	None	Not covered by the combination limitations
Activella-type product	Estradiol	Norethindrone acetate	Different estrogen and progestin
Bijuva	Estradiol	Micronized progesterone	Different estrogen and steroid
Duavee	Conjugated estrogens	Bazedoxifene	Different combination partner
Separate estrogen and progestin tablets	Various	Various	No single claimed compressed tablet
Transdermal estrogen plus oral progestin	Estradiol or other estrogen	Separate oral progestin	Different dosage form and administration

The patent therefore did not create a broad barrier across menopausal hormone therapy. It addressed one combination and one dosage-form strategy.

What manufacturing and intellectual-property barriers remain?

Even after expiration, a manufacturer developing a conjugated-estrogen/MPA product may face technical barriers unrelated to this patent:

Uniform distribution of low-dose hormones.
Stability of conjugated estrogens.
Coating adhesion and layer uniformity.
Control of MPA release from the coating.
Dissolution matching against the reference product.
Bioequivalence requirements for a complex oral dosage form.
Scale-up of sugar-coating operations.
Analytical methods for multiple estrogenic components.
FDA requirements for ANDA product sameness or permissible differences.

These issues can delay generic development but do not restore enforceability to Patent 5,547,948.

What licensing deals affected the patent?

Wyeth was the principal commercial developer associated with Prempro. Pfizer completed its acquisition of Wyeth in 2009, placing Wyeth’s pharmaceutical assets within Pfizer’s portfolio (Pfizer Inc., 2009).

The patent analysis should distinguish ownership from licensing. An assignment or corporate acquisition affects title and enforcement authority; it does not expand the claim scope. No license can make claims 1-6 cover products that lack the required tablet structure, and no license can extend an expired patent term.

What generic launch risks exist today?

Patent 5,547,948 presents no current blocking risk. A generic manufacturer’s remaining exposure would arise from other sources:

Separate unexpired patents listed for the reference product.
FDA exclusivity, if applicable to a later product or supplemental approval.
Labeling and therapeutic-equivalence requirements.
Product-specific bioequivalence failure.
Trademark or trade-dress disputes.
Manufacturing, supply, or quality-control failures.
Separate patents covering alternative formulations or manufacturing processes.

For a generic MPA/conjugated-estrogen product, the principal commercial question is therefore regulatory approval and product development, not this expired patent.

Key Takeaways

U.S. Patent 5,547,948 claims a compressed tablet with conjugated estrogens in the core and a hormonal steroid in a sugar coating.
Claims 4-6 narrow the invention to sucrose, medroxyprogesterone acetate, microcrystalline cellulose, and specified dosage ranges.
The patent does not broadly claim conjugated estrogens, MPA, Prempro’s active ingredients, or all estrogen/progestin products.
Separate tablets, capsules, transdermal systems, polymeric film coatings, and products using other progestins generally fall outside the literal claim structure.
The patent has expired and does not presently block generic entry.
Any current commercial risk must be assessed against other patents, FDA requirements, manufacturing constraints, and market competition.

FAQs

Does Patent 5,547,948 cover Premarin?

No. Premarin contains conjugated estrogens without the claimed MPA-containing sugar coating. The patent is directed to a combination tablet architecture rather than conjugated estrogens alone.

Does a generic need to copy the sugar coating to infringe?

For literal infringement, the product must satisfy the sugar-coating limitation in the asserted claim. A product using a different coating system may avoid literal infringement, subject to the doctrine of equivalents and the patent’s prosecution history.

Does the patent cover a tablet containing conjugated estrogens and MPA in the same core?

Generally no, because the claims require the hormonal steroid, and in claims 4-6 MPA, to be incorporated into the sugar coating.

Is medroxyprogesterone acetate the only steroid covered?

Claims 4-6 are limited to MPA. Claim 1 uses the broader term “hormonal steroid,” but its scope remains limited by the requirement that the steroid be in the sugar coating with release-rate-controlling microcrystalline cellulose.

Can the expired patent still affect FDA approval?

The expired patent cannot itself delay approval or support an infringement action. Other listed patents, regulatory exclusivities, bioequivalence requirements, and product-specific FDA issues may still affect approval.

References

Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations (44th ed.). U.S. Department of Health and Human Services.

Food and Drug Administration. (2024). Prempro prescribing information. U.S. Department of Health and Human Services.

Pfizer Inc. (2009). Pfizer completes acquisition of Wyeth. Pfizer.

United States Patent and Trademark Office. (1996). U.S. Patent No. 5,547,948: Compressed tablet comprising conjugated estrogens and hormonal steroid in a sugar coating. U.S. Department of Commerce.

United States Patent and Trademark Office. (2024). Patent term adjustment and patent term calculation records for U.S. Patent No. 5,547,948. U.S. Department of Commerce.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	002019	⤷ Start Trial
Argentina	005659	⤷ Start Trial
Austria	185482	⤷ Start Trial
Austria	218326	⤷ Start Trial
Australia	4098296	⤷ Start Trial
Australia	705879	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,547,948

Summary for Patent: 5,547,948