United States Drug Patent 4,225,596: Claim Scope, Expiration, Patent Landscape, and Generic Entry Risk

U.S. Patent No. 4,225,596 covers methods of increasing calcium absorption and retention in mammals at risk of bone loss by administering selected active vitamin D compounds. Its practical scope centers on alfacalcidol, calcitriol, dihydrotachysterol-related vitamin D metabolism, and related hydroxylated vitamin D analogs used for osteoporosis or postmenopausal bone loss.

The patent issued on September 30, 1980, and, under the pre-Uruguay Round patent term applicable to the patent, expired no later than September 30, 1997. The claims are therefore no longer enforceable in the United States. The patent has no current blocking effect on generic or competing products, and it cannot support a present Paragraph IV litigation strategy.

What does U.S. Patent 4,225,596 protect?

The patent protects a therapeutic method, not a composition of matter, manufacturing process, or dosage-form invention.

Claim 1 covers administering at least one of five specified vitamin D compounds to a mammal that:

Shows evidence of bone-mass loss; or
Has a physiological tendency toward bone-mass loss.

The claimed therapeutic result is increased calcium absorption and retention.

Claim	Main limitation	Practical scope
1	Administration of one or more listed vitamin D compounds to mammals at risk of bone loss	Broad method-of-treatment claim
2	Daily dose of approximately 0.1 to 1 microgram	Dose-specific dependent claim
3	Oral administration in encapsulated form, with the compound dissolved in a nontoxic ingestible liquid vehicle	Formulation and route limitation
4	Administration to women during and after menopause	Postmenopausal-use limitation
5	Administration to women before menopause	Preventive or premenopausal-use limitation

The listed compounds are:

1α-hydroxycholecalciferol, commonly known as alfacalcidol or alpha-calcidol;
1α-hydroxyergocalciferol;
1,25-dihydroxycholecalciferol, commonly known as calcitriol;
1,25-dihydroxyergocalciferol;
1,24,25-trihydroxycholecalciferol.

The claim does not cover every vitamin D analog. A compound must fall within the express Markush group. Products containing paricalcitol, doxercalciferol, or other later-developed analogs are not automatically within claim 1 merely because they affect calcium or bone metabolism.

How broad is claim 1 of U.S. Patent 4,225,596?

Claim 1 is broad in patient population and therapeutic concept but narrow in chemical identity.

Patient population

The phrase "mammals displaying evidence of, or having a physiological tendency toward, loss of bone mass" reaches both treatment and prevention. It is not limited to a formal osteoporosis diagnosis. Potentially relevant conditions include:

Osteoporosis;
Osteopenia;
Postmenopausal bone loss;
Age-related skeletal loss;
Conditions involving impaired calcium absorption or retention;
Physiological states associated with a tendency toward reduced bone mass.

The claim does not expressly require a measured reduction in bone mineral density. A patient with a recognized physiological risk may fall within the language, subject to proof of the claim elements and applicable claim-construction principles.

Therapeutic result

The claimed objective is "increasing the calcium absorption and retention within the body." This language creates a functional therapeutic limitation. Administration of a listed compound alone may not be enough if the accused use is unrelated to calcium absorption, calcium retention, bone loss, osteoporosis, or a comparable therapeutic objective.

A product label directed to renal osteodystrophy, hypocalcemia, secondary hyperparathyroidism, or another indication could raise a different infringement analysis from a label directed to osteoporosis. The patent does not claim treatment of all diseases for which calcitriol or related analogs may be prescribed.

Chemical scope

The Markush group includes both vitamin D3 and vitamin D2 derivatives. The claim covers the named compounds as chemical entities, regardless of whether they are supplied as a capsule, solution, tablet, or another dosage form, unless a narrower dependent claim is being asserted.

The claim does not expressly require:

A particular salt;
A specific excipient;
A particular manufacturing method;
A specific capsule shell;
A particular release profile;
A defined blood concentration;
A specific calcium intake;
A particular osteoporosis diagnostic threshold.

What does claim 2 protect?

Claim 2 narrows claim 1 to administration of approximately 0.1 to 1 microgram per day.

The range is important because vitamin D analogs are potent at microgram or submicrogram doses. A regimen outside the claimed range would not literally satisfy claim 2, although it could remain within claim 1 if all claim 1 limitations are met.

The phrase "about" introduces ordinary claim-construction flexibility around the endpoints. It does not eliminate the need to establish that the accused dosage is reasonably within the claimed range.

Claim 2 is unlikely to create a meaningful present-day barrier because the underlying patent is expired. Historically, however, it would have been directed at low-dose regimens used in osteoporosis and postmenopausal bone-loss treatment.

What formulation is protected by claim 3?

Claim 3 covers a specific oral dosage configuration:

The active vitamin D compound is in solution;
The liquid vehicle is ingestible and nontoxic;
The preparation is administered orally;
The product is in encapsulated form.

This is narrower than a conventional claim to an oral capsule. A solid suspension, neat powder, tablet, or nonencapsulated oral solution may fall outside the literal language of claim 3.

The claim also requires the compound to be "in solution" in the liquid vehicle. A formulation in which the active is merely dispersed, suspended, or present as undissolved particles may not satisfy this limitation without an equivalent-structure analysis.

Claim 3 does not independently protect:

A specific oil vehicle;
A specific concentration;
A particular gelatin capsule;
A softgel manufacturing process;
A particular stabilizer;
A defined shelf-life specification.

Those limitations would have to come from the patent specification, prosecution history, or a separate patent claim. They cannot be imported into claim 3 merely because they may have been disclosed in the patent.

What uses are covered for menopausal women?

Claims 4 and 5 divide the menopause-related use into two periods.

Claim 4: during and after menopause

Claim 4 covers administration to women during menopause and after menopause. It is directed primarily to treatment or prevention of postmenopausal bone loss.

Claim 5: before menopause

Claim 5 covers administration before the onset of menopause. It reaches prophylactic use in women who have not yet entered menopause but are considered physiologically susceptible to future loss of bone mass.

The claims do not expressly limit the treatment to women with a confirmed osteoporosis diagnosis. They also do not specify a particular menopausal age, hormonal status, bone-density measurement, or duration of therapy.

When did U.S. Patent 4,225,596 expire?

The patent expired in 1997.

Event	Date or status
Patent issued	September 30, 1980
Governing U.S. patent term	Generally 17 years from issuance for this pre-June 8, 1995 patent
Expected statutory expiration	September 30, 1997
Current status	Expired and unenforceable
Patent-term adjustment	Not relevant under the modern PTA framework for this patent
Patent-term extension	No current extension changes the expired status

The patent predates the Hatch-Waxman Act and the modern 20-year term measured from the earliest effective nonprovisional filing date. Patent-term restoration under 35 U.S.C. § 156 was enacted later and generally does not convert an already expired method patent into a live right.

The expiration date eliminates infringement exposure based on the patent itself. It does not eliminate possible exposure under later patents covering:

A specific product;
A newer formulation;
A manufacturing process;
A different indication;
A different vitamin D analog;
A combination therapy;
A delivery system.

Is U.S. Patent 4,225,596 an Orange Book patent?

No current Orange Book exclusivity or enforcement right arises from this patent because it expired in 1997.

The patent claims a method of treatment and could historically have been relevant to an approved drug indication if the patent was listed for that indication. Under the Hatch-Waxman framework, a method-of-use patent can be listed when it claims an approved use and meets the statutory listing requirements. A patent’s age, however, predates the framework and does not itself establish that the patent was ever listed in the Orange Book.

The FDA Orange Book must be consulted for product-specific historical listing information. The patent number alone does not establish:

That the patent was listed against an NDA;
That it was listed for every calcitriol product;
That it covered every approved indication;
That it created a current regulatory stay;
That an ANDA applicant would need to make a Paragraph IV certification today.

Because the patent expired, it cannot support a present 30-month stay or block FDA approval through a current Paragraph IV suit.

Are there Paragraph IV challenges to U.S. Patent 4,225,596?

There is no meaningful current Paragraph IV risk tied to this patent.

A Paragraph IV certification challenges the validity, enforceability, or infringement of a listed patent in connection with an ANDA. That mechanism is relevant only while the patent remains listed and legally capable of delaying approval or supporting an infringement action.

For Patent 4,225,596:

The patent is expired;
The claims are unenforceable;
A generic applicant has no commercial reason to challenge the patent as an active barrier;
A patent-holder lawsuit could not generate a viable infringement remedy based on future conduct;
The patent cannot support a new 30-month stay.

Historical ANDA filings for calcitriol products may have involved Paragraph IV certifications against other patents, including formulation or product patents. Those filings should not be attributed to Patent 4,225,596 without a product-specific FDA and court record.

What drugs and active ingredients are related to the patent?

Calcitriol

Calcitriol is 1,25-dihydroxycholecalciferol and is expressly named in claim 1. It is the closest commercially important active ingredient within the claim set.

Calcitriol has been used in products for:

Hypocalcemia;
Hypoparathyroidism;
Renal osteodystrophy;
Disorders of calcium and phosphate metabolism.

Its presence in a product does not by itself establish infringement. The claimed use must also involve a mammal with evidence of or a tendency toward bone-mass loss and the claimed calcium absorption or retention objective.

Alfacalcidol

Alfacalcidol is 1α-hydroxycholecalciferol and is also expressly included. It is converted in vivo to calcitriol and has been used internationally for disorders involving calcium metabolism and bone disease.

Alfacalcidol has had greater commercial significance outside the United States than in the U.S. market. Its international regulatory and patent position must be analyzed separately by country.

Ergocalciferol analogs

1α-hydroxyergocalciferol and 1,25-dihydroxyergocalciferol are included in the Markush group. Their inclusion broadens the chemical coverage beyond vitamin D3 derivatives.

1,24,25-trihydroxycholecalciferol

This compound is expressly covered, although its commercial importance is substantially lower than that of calcitriol and alfacalcidol.

How does this patent compare with later vitamin D analog patents?

Patent 4,225,596 is an early use patent. Later portfolios generally shifted toward product-specific and indication-specific protection.

Patent category	Example subject matter	Relationship to 4,225,596
Early method patent	Calcium absorption and bone-mass preservation using named vitamin D compounds	Patent 4,225,596
Composition-of-matter patent	New vitamin D analog or stereoisomer	Potentially independent and later-expiring
Formulation patent	Softgel, liquid, stabilized, modified-release, or injectable formulation	May create separate product barriers
Method-of-use patent	Renal osteodystrophy, secondary hyperparathyroidism, osteoporosis, or other indication	May cover a use outside or alongside the older claims
Manufacturing patent	Synthesis, purification, crystallization, or impurity control	Can affect supply without covering the therapeutic use
Combination patent	Vitamin D analog with calcium, phosphate, hormone therapy, or another active	Separate claim scope

Important later vitamin D products include doxercalciferol and paricalcitol. These products were developed for distinct clinical and regulatory uses and are not automatically covered by Patent 4,225,596 because the patent’s Markush group does not expressly name every vitamin D analog.

What manufacturing and intellectual-property barriers remain?

Patent 4,225,596 creates no current manufacturing barrier. A manufacturer can produce a listed compound, formulate it, and sell it in the United States without infringing this expired patent.

Residual barriers may arise from other sources:

Manufacturing complexity

Vitamin D analogs can involve:

Multi-step stereoselective synthesis;
Strict control of hydroxylation chemistry;
Light and oxygen sensitivity;
Low-dose content uniformity requirements;
Impurity and degradant control;
Specialized analytical methods.

These are technical and regulatory barriers, not rights arising from Patent 4,225,596.

Regulatory requirements

A generic applicant may still need to establish:

Pharmaceutical equivalence;
Bioequivalence;
Content uniformity at microgram dosing;
Stability;
Manufacturing controls;
Labeling equivalence or an authorized carve-out;
Compliance with current FDA quality standards.

For an approved reference product, the relevant ANDA pathway depends on the dosage form and the regulatory status of the reference-listed drug. FDA approval status must be evaluated separately from patent expiration.

Later patents

A later patent may cover a particular formulation, crystalline form, delivery system, process, or indication. A freedom-to-operate opinion must therefore search the entire family and product landscape, not only the 1980 patent.

Which companies challenge or compete in this market?

The patent does not identify a current litigation group because it is expired. The relevant competitive field has historically included:

Original developers and licensees of calcitriol products;
Generic manufacturers of calcitriol capsules and related dosage forms;
Suppliers of alfacalcidol outside the United States;
Manufacturers of doxercalciferol and paricalcitol;
Developers of non-vitamin-D osteoporosis therapies.

The principal competitive distinction is therapeutic indication. Calcitriol and related analogs are primarily calcium and phosphate metabolism products, whereas modern osteoporosis competition includes bisphosphonates, denosumab, teriparatide, abaloparatide, romosozumab, and selective estrogen receptor modulators. Those products are not substitutes for purposes of practicing the expired claims, but they compete for some postmenopausal bone-health prescribing.

What is the litigation status of U.S. Patent 4,225,596?

The patent is expired. No current infringement litigation can produce an injunction or damages based solely on claims 1 through 5.

Any historical litigation involving calcitriol, alfacalcidol, or osteoporosis treatment should be separated into:

Litigation involving Patent 4,225,596;
Litigation involving later product or formulation patents;
ANDA litigation concerning an approved reference product;
Regulatory disputes over labeling or therapeutic equivalence;
Contract or license disputes.

A later patent dispute cannot be treated as a continuation of Patent 4,225,596 unless the asserted patent has a direct priority and claim relationship established by the prosecution record.

Did licensing deals create ongoing rights?

Any historical license involving Patent 4,225,596 would have ended as a patent-enforcement matter when the patent expired, subject to contractual provisions that survive expiration. Patent expiration does not automatically terminate every commercial agreement, royalty obligation, confidentiality clause, supply covenant, or know-how restriction.

No continuing royalty or license obligation can be inferred from the patent number alone. A current commercial restriction would require a separate license, settlement, supply agreement, or know-how arrangement.

How strong was the patent estate?

The patent was commercially useful when unexpired because it combined:

A broad therapeutic concept;
Several clinically relevant vitamin D compounds;
Treatment and prevention language;
A low-dose dependent claim;
An oral encapsulated formulation;
Menopause-specific claims.

Its weaknesses included:

No composition-of-matter protection;
No manufacturing protection;
Dependence on named compounds;
Functional treatment-result language;
Potential difficulty proving the intended use and calcium-retention objective;
Limited ability to reach later vitamin D analogs not named in the Markush group;
A relatively early expiration date.

As of 2026, its enforceable patent strength is zero. Its remaining value is historical, technical, and documentary.

What generic launch scenarios exist?

Immediate unrestricted launch

A manufacturer may launch a product practicing the expired claims without licensing Patent 4,225,596, assuming no other enforceable patent or regulatory exclusivity applies.

Paragraph III or no-certification strategy against other patents

For a current product, any Paragraph III or Paragraph IV analysis would concern later listed patents associated with the relevant reference drug, not Patent 4,225,596.

Label carve-out

If a current reference label contains a patented method protected by a live method-of-use patent, an ANDA applicant may seek a section viii statement and omit that indication. Patent 4,225,596 no longer requires such a carve-out.

Non-patent launch delay

Remaining launch constraints may include FDA review, manufacturing readiness, bioequivalence, supply qualification, product liability, and commercial contracting. These are not exclusivity rights under the expired patent.

What is the geographic coverage of the patent?

The patent covered the United States only. U.S. expiration does not determine the status of foreign counterparts.

A global freedom-to-operate review should examine:

Patent families claiming the same compounds or uses;
National-stage filings;
Continuations and divisionals;
European, Japanese, Canadian, and other national rights;
Supplementary protection certificates;
Local regulatory exclusivity;
National rules governing medical-use claims.

Any foreign counterpart with a later expiration would require a separate country-by-country analysis. The U.S. patent number does not establish foreign protection.

Key Takeaways

U.S. Patent 4,225,596 is an expired method-of-treatment patent.
Claim 1 covers five specified hydroxylated vitamin D compounds used to increase calcium absorption and retention in mammals at risk of bone loss.
Claims 2 through 5 narrow the invention by dose, oral encapsulated solution, and menopausal status.
The patent does not broadly cover every vitamin D analog, osteoporosis product, or calcium-regulating therapy.
The patent expired no later than September 30, 1997.
It cannot support current infringement litigation, a Paragraph IV stay, or a present U.S. market-entry block.
Current risk must be assessed against later composition, formulation, manufacturing, and method-of-use patents.
The patent’s historical commercial relevance is greatest for calcitriol and alfacalcidol.
No continuing license, royalty, or settlement obligation can be inferred from the patent itself.
Foreign patent status must be analyzed independently.

FAQs

Does Patent 4,225,596 cover calcitriol for kidney disease?

Not automatically. Calcitriol is one of the named compounds, but the asserted use must satisfy the claim’s bone-mass-loss and calcium absorption or retention limitations. Treatment directed solely to renal disease may require a separate infringement analysis.

Can a generic manufacturer sell calcitriol for osteoporosis today?

Patent 4,225,596 does not prevent that sale because the patent expired. The manufacturer must still satisfy FDA requirements and avoid infringement of any later unexpired patent.

Does the patent cover vitamin D3 or cholecalciferol?

No. The claims identify hydroxylated compounds, including 1α-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol. Ordinary cholecalciferol, also known as vitamin D3, is not expressly listed.

Are paricalcitol and doxercalciferol covered by claim 1?

Not by name. Their coverage would depend on whether the specific chemical structure falls within one of the claimed compounds. They should not be presumed to fall within the Markush group solely because they are vitamin D analogs.

Could a foreign patent based on the same invention still be active?

Possibly. The U.S. expiration date does not determine foreign patent expiration. Each foreign family member, national filing, supplementary protection right, and local regulatory exclusivity period requires separate analysis.

References

U.S. Patent No. 4,225,596. (1980). United States Patent and Trademark Office.
United States Code, 35 U.S.C. §§ 154, 156, 271, and 282.
Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations (Orange Book). U.S. Department of Health and Human Services.
Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs. U.S. Department of Health and Human Services.
Food and Drug Administration. (2024). Abbreviated new drug application regulations and patent certifications. U.S. Department of Health and Human Services.
World Intellectual Property Organization. (2024). PATENTSCOPE patent database. World Intellectual Property Organization.

Summary for Patent: 4,225,596