US Patent 8,389,542: Lubiprostone Dosage-Unit Claims, Patent Scope and Generic-Entry Landscape

US Patent 8,389,542 protects a narrow but commercially important product configuration for lubiprostone, the active ingredient in Amitiza. Its independent claim is directed to an oral dosage unit containing approximately 24 micrograms of a difluorinated prostaglandin analog, together with a pharmaceutically suitable excipient. The claim maps directly to Amitiza 24 mcg capsules used for chronic idiopathic constipation and opioid-induced constipation.

The patent does not broadly claim lubiprostone as a molecule. It claims a defined dose, dosage-unit format, excipient environment and therapeutic-use context. The patent issued March 12, 2013, from the Sucampo lubiprostone patent family. Its original 20-year term runs from the relevant 2005 nonprovisional filing date, placing the nominal expiration in September 2025, subject to any patent-term adjustment or regulatory extension recorded by the USPTO and FDA.

What drug does US Patent 8,389,542 protect?

The claimed prostaglandin analog is lubiprostone when the Formula (I) substituents are interpreted as specified in the claims:

Claim element	Scope
Active ingredient	Difluorinated prostaglandin analog corresponding to lubiprostone
A1 and A2	Fluorine atoms
B	Carboxylic acid, or pharmaceutically acceptable salt, ester or amide
Dose	24 mcg plus or minus 10% in claim 1
Exact dose	24 mcg in claims 10-13
Dosage form	A dosage unit
Excipient	Broadly, a pharmaceutically suitable excipient
Narrow excipient	An orally acceptable medium-chain fatty acid
Use	Human use, including relieving or preventing constipation

Lubiprostone is a bicyclic prostaglandin analog and chloride-channel activator. Amitiza 24 mcg capsules contain lubiprostone in a soft gelatin oral dosage form with medium-chain triglyceride excipients. The FDA label identifies Amitiza for chronic idiopathic constipation, opioid-induced constipation in adults with chronic non-cancer pain, and irritable bowel syndrome with constipation in adult women [2].

How broad are the claims of US 8,389,542?

Claim 1 is the controlling independent claim. It requires four principal limitations:

A dosage unit.
A prostaglandin analog within the claimed structural definition.
A 24 mcg dose with a permitted range of 21.6 to 26.4 mcg.
A pharmaceutically suitable excipient.

The claim is product-focused. It does not require a manufacturing process, a specific capsule shell, a particular release profile or a constipation indication. A product could infringe claim 1 even if its labeling omitted constipation treatment, provided the product contains the claimed active ingredient and dose.

What dose range does claim 1 cover?

The phrase “24 μg +/- 10%” covers:

Calculation	Dose
Lower boundary	21.6 mcg
Nominal dose	24 mcg
Upper boundary	26.4 mcg

Claims 10 through 13 narrow the scope to a dosage unit containing 24 mcg. Claims 10 and 1 overlap because an exact 24 mcg product falls within the 21.6-to-26.4 mcg range.

The dose limitation is commercially significant. A generic manufacturer offering an 8 mcg lubiprostone product would not fall within the express 24 mcg limitation. A 24 mcg product would be the principal target.

Does the patent claim lubiprostone itself?

No. The patent does not operate as a compound patent covering every use and formulation of lubiprostone. It claims a dosage unit containing a structurally defined analog at a specified dose.

The patent therefore has less molecule-level breadth than a composition-of-matter patent. Its value lies in blocking a commercially relevant finished dosage strength, particularly the 24 mcg oral capsule.

What do the tautomer limitations cover?

Claims 2 and 3 separately identify the monocyclic and bicyclic tautomers of the Formula (I) compound. These claims reduce interpretive disputes over whether a particular chemical representation is the monocyclic or bicyclic form.

Because the claims use “and/or its tautomers,” the patent attempts to prevent a design-around based solely on representing lubiprostone in a different tautomeric form. A generic product would not avoid the claims merely by using a different nomenclature or structural depiction if the active ingredient is chemically the same claimed analog.

What formulations are protected by US 8,389,542?

The broadest formulation requirement is “a pharmaceutically suitable excipient.” That language potentially reaches multiple dosage-unit formulations, subject to written-description, enablement and claim-construction limits.

The dependent claims create progressively narrower formulation categories:

Claims	Formulation limitation
1-3, 6, 10-11	Any pharmaceutically suitable excipient
4	Orally acceptable excipient
5, 9, 12-13	Medium-chain fatty acid excipient
10-13	Exact 24 mcg dose
13	Exact 24 mcg dose, carboxylic acid form and medium-chain fatty acid

The narrowest commercially relevant claim is claim 13. It requires:

24 mcg of the claimed prostaglandin analog;
B as a carboxylic acid;
a medium-chain fatty acid excipient.

Amitiza’s liquid-filled soft-gelatin capsule formulation is closely aligned with these limitations. The FDA-approved labeling describes lubiprostone capsules containing medium-chain triglycerides and other capsule excipients [2].

How does the claim hierarchy affect infringement risk?

The claims create several infringement paths.

Broad product risk

A 24 mcg oral lubiprostone capsule with any pharmaceutically suitable excipient would present the primary claim 1 risk, assuming the patent remained enforceable.

Narrow formulation risk

A product using a medium-chain fatty acid or medium-chain triglyceride excipient would face claims 5, 9, 12 and 13. A formulation using a different excipient system could avoid those dependent claims while still implicating claim 1.

Dosage-form risk

The claims are not expressly limited to capsules. “Dosage unit” can include tablets, soft-gelatin capsules, hard capsules, sachets or other unit-dose forms, subject to the specification and ordinary claim construction. A change from a soft-gelatin capsule to a tablet would not automatically avoid claim 1.

Use risk

Claims 7 and 8 add human suitability and constipation use. They are narrower than claim 1. A generic manufacturer could face product claims even if it uses a restricted label, while method-of-use liability would depend on the approved labeling and induced-infringement facts.

What is the patent expiration date?

The relevant patent chronology is:

Event	Date
Earliest claimed priority	September 17, 2004, according to the family record
Relevant US nonprovisional filing period	September 2005
Patent issued	March 12, 2013
Nominal 20-year term	September 2025
Commercial relevance after nominal expiry	Dependent on any recorded PTA, PTE or terminal disclaimer

The patent’s nominal term is materially different from the grant date. A patent issued in 2013 does not ordinarily expire 20 years after issuance. US patent term is generally measured from the earliest effective nonprovisional filing date, subject to statutory adjustments under 35 U.S.C. §§ 154 and 156 [4].

For diligence, the controlling sources are the USPTO Patent Center term adjustment record and the current FDA Orange Book listing. The Orange Book may list a patent after grant but does not itself extend patent term.

What is the Orange Book status of US 8,389,542?

US Patent 8,389,542 was associated with the Amitiza patent estate and was relevant to abbreviated new drug application challenges directed to lubiprostone capsules. The patent’s practical importance depended on whether it was listed for the specific 8 mcg or 24 mcg approved strengths and whether the listed claims covered the approved product.

An Orange Book listing does not establish validity or enforceability. It gives an ANDA applicant a statutory basis to submit:

Paragraph I certification, if the patent information is not applicable;
Paragraph II certification, if the patent has expired;
Paragraph III certification, accepting approval only after patent expiration; or
Paragraph IV certification, asserting that the patent is invalid, unenforceable or not infringed.

Because the principal claim covers the 24 mcg dosage unit, a Paragraph IV challenge to the 24 mcg strength would be more directly relevant than an application limited to 8 mcg.

Which companies challenged the Amitiza patent estate?

The Amitiza estate was challenged through ANDA litigation involving generic pharmaceutical companies, including Par Pharmaceutical and Dr. Reddy’s Laboratories. The disputes involved multiple Sucampo patents, not only US 8,389,542. The asserted portfolio included compound, formulation, dosage and method-of-use patents.

Patent litigation involving Amitiza typically required analysis of:

Whether the ANDA product contained the claimed 24 mcg dosage unit;
Whether the generic formulation used covered excipients;
Whether the asserted claims were anticipated or obvious;
Whether the claims were enabled across the full dosage and formulation scope;
Whether the generic label induced infringement of constipation indications;
Whether settlement agreements delayed commercial entry.

A Paragraph IV filing itself does not invalidate a patent. The applicant must prevail in litigation, obtain a favorable settlement, or wait for expiry.

What settlement agreements affected generic launch timing?

Amitiza generic-entry timing was controlled by a combination of patent litigation, Hatch-Waxman settlement terms and FDA approval timing. Publicly reported settlements involving Sucampo and generic applicants allowed certain generic launches before the latest listed patent dates, subject to agreed entry dates and regulatory conditions.

The 180-day first-filer exclusivity period also mattered. If a qualifying ANDA applicant received first-filer status and the patent dispute was resolved, later applicants could remain blocked until the statutory exclusivity period was forfeited or expired.

The existence of a settlement did not eliminate portfolio risk for later filers. A later ANDA applicant could still face listed patents, formulation claims and method-of-use claims even after an earlier generic obtained an agreed entry date.

How strong is the patent estate for lubiprostone?

The 8,389,542 patent is best characterized as a medium-strength dosage patent rather than a foundational patent.

Factor	Assessment
Molecule coverage	Limited; it does not broadly claim lubiprostone as a compound
Dose coverage	Strong for 24 mcg dosage units
Formulation breadth	Broad at claim 1, narrower in dependent claims
Design-around potential	Moderate; alternative dose, excipient or dosage strategy may reduce exposure
Commercial relevance	High because 24 mcg is a major approved strength
Biosimilar relevance	None; lubiprostone is a small molecule
Post-expiry value	Limited, except for prosecution history and family analysis

The strongest infringement theory concerns a conventional 24 mcg oral lubiprostone product. The strongest validity attacks would likely focus on prior-art disclosure of lubiprostone dosage units, obviousness of the 24 mcg dose and the breadth of the excipient language.

What generic-entry risks exist for Amitiza?

The principal generic launch scenarios are:

Scenario 1: 24 mcg capsule after patent expiry

This is the lowest residual patent risk once all relevant listed patents have expired or been held unenforceable. Competition would then depend primarily on FDA approval, bioequivalence and manufacturing capacity.

Scenario 2: 24 mcg capsule before final patent expiry

This requires a Paragraph IV pathway, litigation resolution or a settlement with an agreed launch date. The generic applicant would face the highest exposure to the dosage-unit claims.

Scenario 3: 8 mcg product

An 8 mcg product does not meet the express 24 mcg limitation in US 8,389,542. It may still implicate other Amitiza patents, labeling claims or formulation patents.

Scenario 4: Alternative formulation

A non-capsule or non-medium-chain-fatty-acid formulation may avoid some dependent claims. It would not necessarily avoid claim 1, which requires only a pharmaceutically suitable excipient.

Are biosimilar risks relevant?

No. Lubiprostone is a chemically synthesized small molecule, not a biologic. The relevant regulatory route is an ANDA under section 505(j) of the Federal Food, Drug, and Cosmetic Act, not a biosimilar application under section 351(k) of the Public Health Service Act.

The competitive risks are therefore generic substitution, ANDA litigation, 180-day exclusivity and formulation differentiation. Biosimilar interchangeability and reference-biologic exclusivity do not apply.

How does US 8,389,542 compare with other lubiprostone patents?

The lubiprostone portfolio generally divides into four categories:

Patent category	Typical protection
Compound patents	Lubiprostone structure and related prostaglandin analogs
Dosage patents	8 mcg or 24 mcg unit doses
Formulation patents	Capsules, excipient systems and stability characteristics
Method patents	Treatment of constipation or related gastrointestinal conditions

US 8,389,542 is a dosage and formulation patent. It is narrower than a compound patent but more directly tied to the marketed 24 mcg product. Its commercial leverage was strongest before expiry, when a generic could not freely launch an equivalent 24 mcg dosage unit without addressing the claim.

Key Takeaways

US 8,389,542 targets a 24 mcg dosage unit containing lubiprostone or the claimed difluorinated prostaglandin analog.
Claim 1 covers approximately 21.6 to 26.4 mcg, while claims 10-13 focus on exactly 24 mcg.
The patent reaches broad excipient categories through claim 1 and medium-chain fatty acid formulations through dependent claims.
It does not broadly claim lubiprostone as a molecule.
Amitiza 24 mcg capsules are the principal commercial product aligned with the claim set.
The patent is a small-molecule dosage patent, so biosimilar rules do not apply.
Generic applicants would use the ANDA pathway and could challenge listed claims through Paragraph IV certifications.
The patent’s nominal 20-year term runs from the relevant 2005 US filing period, placing expiration in September 2025 before any applicable term adjustment or extension.
Other Amitiza patents may have created separate barriers even after US 8,389,542 expired.
The highest historical infringement risk involved a 24 mcg oral lubiprostone product using a conventional excipient system.

FAQs About US Patent 8,389,542

Does a 24 mcg lubiprostone tablet infringe US 8,389,542?

It could implicate claim 1 because the claim is directed to a dosage unit and is not expressly limited to a capsule. The outcome would depend on the active ingredient, dose, excipient and the patent’s enforceability at the relevant time.

Does an 8 mcg lubiprostone product infringe this patent?

An 8 mcg product does not meet the express 24 mcg limitation or the 21.6-to-26.4 mcg range in claim 1. Other patents in the Amitiza portfolio could still be relevant.

Can a generic avoid the patent by changing the excipient?

Changing the excipient could avoid claims limited to medium-chain fatty acids, but it would not automatically avoid claim 1 because claim 1 requires only a pharmaceutically suitable excipient.

Is lubiprostone protected by a biologic exclusivity period?

No. Lubiprostone is a small-molecule drug regulated through the generic-drug framework. Biologic reference-product exclusivity and biosimilar interchangeability provisions do not apply.

Does patent expiration automatically permit immediate generic launch?

No. The generic product still requires FDA approval, satisfactory bioequivalence, resolution of any remaining listed patents and compliance with applicable labeling and exclusivity requirements.

References

U.S. Patent No. 8,389,542. (2013). Dosage forms comprising a prostaglandin analog. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2023). Amitiza (lubiprostone) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA, Orange Book.
U.S. Patent and Trademark Office. (2024). Patent term adjustment and patent term extension provisions. USPTO.
U.S. Food and Drug Administration. (2024). Hatch-Waxman amendments and abbreviated new drug applications. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	2298314	⤷ Start Trial	92826	Luxembourg	⤷ Start Trial
Argentina	037524	⤷ Start Trial
Argentina	098997	⤷ Start Trial
Austria	522218	⤷ Start Trial
Brazil	0214075	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,389,542

Summary for Patent: 8,389,542