United States Drug Patent 4,459,310: Claim Scope, Misoprostol Coverage, Expiration, and Patent Landscape

US Patent No. 4,459,310 covered the use of specified prostaglandins, including misoprostol, to lower elevated cholesterol in humans. The patent issued July 10, 1984, and its original 17-year patent term expired July 10, 2001. It does not create a current United States exclusivity barrier for generic misoprostol or other products that practice the claimed method.[1]

The patent is important historically because claim 3 expressly names misoprostol. Its commercial scope was narrower than a product patent: it covered a therapeutic method, not misoprostol itself, a formulation, a manufacturing process, or every use of the molecule.

What does US Patent 4,459,310 cover?

The patent claims methods for lowering elevated cholesterol by administering an effective amount of a defined prostaglandin to a human patient with elevated cholesterol.

Claim	Type	Principal subject matter	Practical scope
1	Independent method claim	Administration of a prostaglandin genus defined by structural variables	Broadest claim, subject to the chemical limitations and patient-use limitations
2	Dependent method claim	A narrower prostaglandin species or subgroup shown in the patent’s chemical formula	Narrows claim 1 through a more specific structure
3	Dependent method claim	Administration of misoprostol	Expressly covers misoprostol for cholesterol lowering

Claim 3 incorporates all limitations of claim 1 and adds the requirement that the administered prostaglandin is misoprostol. It therefore requires:

A human patient;
Elevated cholesterol in that patient;
Administration of misoprostol;
An effective cholesterol-lowering amount; and
Administration for the purpose or therapeutic result of lowering elevated cholesterol.

The claim is not a claim to misoprostol as a chemical compound.

How broad is claim 1?

Claim 1 is a Markush-type method claim. It covers a family of prostaglandins defined by substituent choices:

R1 is hydrogen or lower alkyl;
R2 and R3 are hydrogen or lower alkanoyl;
R4 is lower alkyl; and
x is either -CH2-CH2- or -CH=CH-.

The claim reaches compounds satisfying the stated structural formula and variable definitions. The structural limitations are cumulative. A compound must fit the formula and each permitted substituent range.

What does “lower alkyl” mean?

“Lower alkyl” ordinarily refers to a relatively short, straight-chain or branched hydrocarbon substituent, commonly containing one to six carbon atoms unless the specification defines the term differently. The patent specification and prosecution history control the final interpretation.

“Lower alkanoyl” ordinarily refers to a short-chain acyl group derived from a lower carboxylic acid, such as acetyl or propionyl. The precise scope depends on the patent’s specification and the accepted claim construction.

Why the structural formula matters

The text of claim 1 alone does not identify every stereochemical, positional, and ring-substitution requirement. Those requirements are embedded in the chemical formula reproduced in the patent. A compound must match the complete formula, not merely the listed R-group options.

For infringement analysis, a prostaglandin with cholesterol-lowering activity is not sufficient by itself. The accused compound must also fall within the structural genus.

What does claim 2 protect?

Claim 2 is a dependent claim and therefore includes every limitation of claim 1. It further limits the method to the more specific prostaglandin formula depicted in the patent.

The dependent structure gives the patent a narrower fallback position if the broad genus in claim 1 is challenged. Claim 2 may also capture a defined subgroup that is commercially or pharmacologically more relevant than the full genus.

Because the chemical drawing for claim 2 is not reproduced in the text provided, the exact species-level boundaries of claim 2 cannot be stated reliably from the claim language alone. The printed chemical formula in US 4,459,310 controls.

Does claim 3 cover misoprostol?

Yes. Claim 3 expressly recites misoprostol.

Misoprostol is a synthetic prostaglandin E1 analog used primarily for prevention of nonsteroidal anti-inflammatory drug-related gastric ulcers, medical termination of pregnancy in specified regimens, cervical ripening, and obstetric indications. US 4,459,310 claimed its use for a different indication: lowering elevated cholesterol.

Claim 3 does not cover:

Misoprostol as a compound;
Misoprostol tablets as a formulation;
The Cytotec brand generally;
Every therapeutic use of misoprostol;
Manufacture, synthesis, or packaging of misoprostol; or
Use in ulcer prevention or obstetric indications.

A misoprostol product would have implicated claim 3 only when administered to a human with elevated cholesterol in an effective cholesterol-lowering amount and for the claimed cholesterol-lowering method.

When did US Patent 4,459,310 expire?

US 4,459,310 issued July 10, 1984. As a pre-1995 United States patent, its ordinary term was 17 years from grant. On that basis, the patent expired July 10, 2001.[1]

Event	Date
Patent issued	July 10, 1984
Standard patent term	17 years from issuance
Expiration	July 10, 2001
Current status	Expired

The expiration ended enforceable patent rights under the asserted claims. A party cannot now be enjoined for practicing claim 3, and a Paragraph IV challenge directed solely to this patent has no current commercial value because the patent is no longer enforceable.

Was the patent a product patent or a method-of-use patent?

US 4,459,310 was a method-of-use patent.

The claims require administering a prostaglandin to a human with elevated cholesterol. They do not claim:

The active pharmaceutical ingredient in isolation;
A pharmaceutical composition;
A dosage form;
A salt, ester, crystal, or polymorph;
A manufacturing process;
A tablet coating;
A combination product; or
A specific commercial brand.

This distinction matters in generic-drug analysis. A generic manufacturer could have faced method-of-use exposure during the patent term if its labeling encouraged the claimed cholesterol-lowering use. The same manufacturer could avoid infringement if its product and labeling were limited to unclaimed indications, subject to the applicable statutory and factual analysis.

What was the Orange Book status of US 4,459,310?

US 4,459,310 is not a current Orange Book exclusivity obstacle.

The FDA Orange Book identifies patents and regulatory exclusivities associated with approved drug products. Misoprostol was approved in the United States under NDA 019268 for Cytotec, originally associated with G.D. Searle & Co. FDA-approved generic misoprostol products later entered the market.[2][3]

A method-of-use patent can be listed in the Orange Book if it claims an approved use and satisfies FDA listing requirements. Even if US 4,459,310 was historically associated with the misoprostol product’s patent landscape, its July 10, 2001 expiration means it has no present blocking effect.

Regulatory issue	Assessment
Active patent exclusivity from US 4,459,310	None
Current Paragraph IV significance	None
Current patent-based generic blocking period	None
Biosimilar relevance	None
Current misoprostol market access	Governed by active product, formulation, labeling, and manufacturing rights, not this expired patent

Did the patent protect a misoprostol formulation?

No. The claims provided do not recite a tablet, capsule, liquid, dosage unit, excipient, coating, release profile, or stability limitation.

A later formulation patent could have covered a particular misoprostol formulation even though US 4,459,310 covered a therapeutic use. Such a later patent would have required separate analysis of:

The composition;
The dosage form;
The amount of misoprostol;
Excipients;
Stability requirements;
Packaging;
Manufacturing steps; and
Expiration and Orange Book listing status.

US 4,459,310 itself supplies no formulation protection.

What manufacturing and intellectual-property barriers existed?

The patent did not claim synthesis or manufacturing. It therefore did not prevent a manufacturer from producing misoprostol through a non-infringing process during the patent term, provided the manufacturer did not practice the claimed cholesterol-lowering method.

The main historical barriers would have come from separate rights covering:

Misoprostol composition or analogs;
Prostaglandin synthesis;
Pharmaceutical formulations;
Stability and packaging;
Approved labeling;
Regulatory exclusivity; and
Commercial know-how.

Because US 4,459,310 expired in 2001, it no longer creates a manufacturing barrier. Any present barrier must arise from a separate unexpired patent, regulatory requirement, trade secret, supply constraint, or product-specific approval issue.

Were Paragraph IV challenges or generic litigation associated with this patent?

A Paragraph IV certification is relevant only while a listed patent remains enforceable or otherwise affects approval timing. For an expired patent, a current ANDA applicant does not obtain a meaningful commercial advantage by challenging the patent.

The patent’s method-of-use structure also limits the likely scope of a generic dispute. A litigation case would have focused on questions such as:

Whether the accused misoprostol product’s label encouraged cholesterol treatment;
Whether the patient population had elevated cholesterol;
Whether the dosage was an effective cholesterol-lowering amount;
Whether the administered compound was misoprostol; and
Whether the claims were valid and enforceable.

A label limited to ulcer prevention or another non-claimed use would not, by itself, practice claim 3. The analysis would depend on the complete label, promotional conduct, physician instructions, and the statutory basis for any induced-infringement theory.

No current Paragraph IV risk arises from US 4,459,310 because the patent expired more than two decades ago.

How does this patent compare with misoprostol composition patents?

Protection category	Covered by US 4,459,310?	Commercial significance today
Misoprostol compound	No	Must be assessed under separate composition patents, all of which may be expired or otherwise unavailable
Cholesterol-lowering use	Yes	Expired July 10, 2001
Ulcer-prevention use	No, based on the claims provided	Requires separate use-claim analysis
Obstetric use	No, based on the claims provided	Requires separate use-claim analysis
Tablet formulation	No	Separate formulation patents may apply
Manufacturing process	No	Separate process patents may apply
Packaging or stability	No	Separate technical rights may apply
Generic labeling	Only to the extent it practices the claimed cholesterol use	No current barrier from this patent

The key distinction is between molecule, formulation, and use. A company could have held rights in one category without controlling the others.

Which companies were commercially affected?

The historical reference product was Cytotec, marketed by G.D. Searle & Co., later associated with Pfizer through corporate ownership and product portfolio changes.[3] The patent’s commercial exposure was tied to the cholesterol-lowering use of prostaglandins, not to all sales of Cytotec.

The patent did not provide a basis to calculate total Cytotec revenue because it did not cover the principal ulcer-prevention indication. Any revenue attributable specifically to the patented cholesterol indication would require indication-level sales data, which is generally not reported separately in public company filings.

Current revenue exposure from this patent is zero as a matter of enforceable patent rights. Misoprostol market revenue may continue, but it is not protected by US 4,459,310.

How strong was the patent estate?

Claim strength during the term

The patent had several characteristics that would have affected historical strength:

Claim 1 used a broad chemical genus;
Claim 2 provided a narrower structural fallback;
Claim 3 expressly identified misoprostol;
The claims were limited to treatment of elevated cholesterol;
The claims required administration to humans; and
The patent did not claim the misoprostol product itself.

Claim 3 was likely easier to map to a specific molecule than claim 1, but it also had a narrow indication requirement. Claim 1 had broader chemical reach but greater vulnerability to structural and prior-art disputes.

Strength today

The patent has no present enforcement strength because it expired. Historical validity questions no longer create practical launch risk for ordinary commercial activity, although they could remain relevant to disputes concerning conduct during the patent term.

What generic launch scenarios existed?

During the patent term, the principal scenarios were:

A generic misoprostol applicant could seek approval with labeling that excluded the patented cholesterol-lowering use.
An applicant could challenge the patent under Paragraph IV if the patent was listed and enforceable.
A manufacturer could market misoprostol for unclaimed indications while avoiding promotion of cholesterol treatment.
A competitor could wait for the July 10, 2001 expiration and then market without this patent-based restriction.

After expiration, the fourth scenario became the operative position. Generic entry is no longer constrained by US 4,459,310.

Does the patent create biosimilar risk?

No. Misoprostol is a small-molecule drug, not a biologic. Biosimilar approval under the Public Health Service Act is therefore irrelevant. Generic misoprostol products proceed through the abbreviated new drug application pathway under section 505(j) of the Federal Food, Drug, and Cosmetic Act, subject to product-specific regulatory requirements.[4]

What is the geographic coverage?

The patent covered the United States only. It did not create rights in Canada, Europe, Japan, or other jurisdictions. Foreign counterparts, if any, required separate filing, prosecution, and term analysis.

A company evaluating global launch risk must review:

Foreign composition patents;
Foreign use patents;
Formulation and process patents;
Patent-term adjustments or supplementary protection certificates;
National regulatory exclusivity; and
Local labeling rules.

Expiration of US 4,459,310 does not determine the status of foreign patent families.

Key Takeaways

US Patent 4,459,310 claimed prostaglandin methods for lowering elevated cholesterol.
Claim 3 expressly covered administering misoprostol for that purpose.
The patent did not claim misoprostol as a compound or protect a formulation or manufacturing process.
The patent issued July 10, 1984, and expired July 10, 2001.
It presents no current United States patent barrier to generic misoprostol.
Paragraph IV and biosimilar issues are not currently material for this expired method patent.
Any current risk must come from separate composition, formulation, process, labeling, regulatory, or foreign patents.
The exact scope of claim 2 depends on the chemical formula reproduced in the issued patent.

FAQs

Does US 4,459,310 cover Cytotec for stomach-ulcer prevention?

No. The claims provided are limited to lowering elevated cholesterol. They do not claim ulcer prevention.

Could a generic misoprostol manufacturer have infringed claim 3 by selling tablets?

Selling tablets alone would not necessarily practice claim 3. The infringement analysis would turn on whether the manufacturer’s conduct induced administration of misoprostol to humans with elevated cholesterol in an effective cholesterol-lowering amount.

Is US 4,459,310 still listed as an active patent for misoprostol?

It is expired. Any historical listing does not create current enforceable exclusivity after July 10, 2001.

Does the patent cover misoprostol use in pregnancy-related care?

Not under the claims provided. Claim 3 is limited to cholesterol lowering, not cervical ripening, labor induction, or pregnancy termination.

Can this patent block a new cholesterol drug today?

No. The patent cannot block a current cholesterol drug because its term expired. A new product would require analysis against separate unexpired patents and regulatory rights.

References

United States Patent and Trademark Office. (1984). US Patent No. 4,459,310, Prostaglandins for lowering cholesterol. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. U.S. Department of Health and Human Services.
Pfizer Inc. (n.d.). Cytotec (misoprostol) prescribing information. U.S. Food and Drug Administration.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application (ANDA) process. U.S. Department of Health and Human Services.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	27104	⤷ Start Trial
Germany	3463613	⤷ Start Trial
European Patent Office	0129908	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,459,310

Summary for Patent: 4,459,310