US Patent 4,216,211 covers the use of organophosphonates to increase blood 2,3-diphosphoglycerate, with narrower claims directed to etidronic acid salts, methanediphosphonic acid, and methanedichlorodiphosphonic acid. The patent issued August 5, 1980, and its ordinary 17-year term expired August 5, 1997. It therefore presents no current U.S. patent barrier to generic or other commercial use.

US Drug Patent 4,216,211: Claim Scope, Expiration, and Organophosphonate Patent Landscape

What does US Patent 4,216,211 cover?

US Patent 4,216,211 covers a therapeutic process for increasing the concentration of 2,3-diphosphoglycerate, commonly abbreviated 2,3-DPG or 2,3-BPG, in the blood of humans or lower animals.

The patent does not claim a single drug product. Its principal claim is a broad method-of-treatment claim covering administration of specified organophosphonate compounds in an amount sufficient to increase blood 2,3-DPG.

The patent’s five claims divide into:

Claim	Subject matter	Scope
1	Administration of defined vicinal or geminal organophosphonates	Broad genus claim
2	Ethane-1-hydroxy-1,1-diphosphonic acid and salts or esters	Species claim
3	Sodium salt of ethane-1-hydroxy-1,1-diphosphonic acid	Narrow species claim
4	Methanediphosphonic acid and salts or esters	Species claim
5	Methanedichlorodiphosphonic acid and salts or esters	Species claim

The patent is directed to pharmacological modulation of red-cell oxygen transport. 2,3-DPG binds deoxygenated hemoglobin and reduces hemoglobin’s oxygen affinity. Increasing 2,3-DPG was therefore proposed as a means of shifting oxygen delivery to tissues.

What is the broadest claim in US 4,216,211?

Claim 1 is the broadest claim. It requires five principal elements:

A human or lower animal in need of treatment.
Administration of an organophosphonate compound.
A compound falling within one of two structural classes, described as vicinal or geminal organophosphonates.
A pharmaceutically acceptable salt of a qualifying compound, where applicable.
An amount sufficient to increase blood 2,3-DPG.

The claim uses a Markush structure. It permits a broad range of substituents, including:

Hydrogen;
Hydroxymethyl;
C1-C20 alkyl or cycloalkyl;
C2-C20 alkenyl;
Aryl;
Phenylethyl;
Benzyl;
Halogen;
Amino or substituted amino groups;
Carboxymethyl;
Phosphonomethyl;
Hydroxyphosphonomethyl; and
Substituted phosphonoethyl groups.

The disclosed variable n ranges from 1 to approximately 10. That range substantially expands the potential compound set beyond the three expressly identified compounds in claims 2 through 5.

Why the “sufficient amount” language matters

The phrase “sufficient ... to increase” is a functional limitation. A product or administration method would need to satisfy both the structural and therapeutic requirements of the claim.

A compound that falls within the Markush formula would not automatically infringe the claim merely because of its chemical structure. The claimed use must also involve administration to a subject in need of treatment and an amount capable of increasing blood 2,3-DPG.

Conversely, a compound outside the disclosed structural formula would not fall within claim 1, even if it increased 2,3-DPG through a different mechanism.

What compounds are specifically protected by claims 2 through 5?

Claim 2: Etidronic acid

Claim 2 identifies ethane-1-hydroxy-1,1-diphosphonic acid, commonly called etidronic acid or etidronate when used in salt form.

Relevant identifiers include:

Item	Description
Common name	Etidronic acid
Common salt	Etidronate disodium
Chemical class	Bisphosphonate
Patent claim	Claim 2
Therapeutic context	Administration to increase blood 2,3-DPG

Claim 2 covers the compound and pharmaceutically acceptable salts and esters. It is narrower than claim 1 because it limits the active ingredient to one named bisphosphonate.

Claim 3: Sodium etidronate

Claim 3 is narrower still. It covers a sodium salt of ethane-1-hydroxy-1,1-diphosphonic acid.

Commercial etidronate products generally used etidronate disodium. Claim 3 would have been the most commercially relevant claim if a product had been developed and marketed specifically for the claimed 2,3-DPG indication during the patent term.

The claim is use-limited. It does not claim every use of etidronate disodium. A product used for an unrelated indication, such as an approved bone disorder, would not necessarily practice claim 3.

Claim 4: Methanediphosphonic acid

Claim 4 covers methanediphosphonic acid and its pharmaceutically acceptable salts and esters.

This claim is structurally narrower than claim 1 but potentially broad across salt and ester forms. It does not require the sodium salt specified in claim 3.

Claim 5: Methanedichlorodiphosphonic acid

Claim 5 covers methanedichlorodiphosphonic acid and its pharmaceutically acceptable salts and esters.

The claim specifically identifies chlorine substitution on the methanediphosphonic acid framework. A competing organophosphonate would need to be evaluated against the structural limitations of claim 1 rather than claim 5.

When did US Patent 4,216,211 expire?

US Patent 4,216,211 issued on August 5, 1980. For a U.S. patent governed by the pre-1995 term rules, the ordinary term was 17 years from grant. On that basis, the patent expired on August 5, 1997.[1][2]

Event	Date
Patent issued	August 5, 1980
Ordinary patent term	17 years from issue
Expiration	August 5, 1997
Current enforceability	None after expiration

The patent is therefore public-domain technology in the United States. A later developer cannot obtain a new patent merely by practicing the expired claims. It could, however, obtain separate patent protection for a new formulation, delivery system, manufacturing process, dosage regimen, combination, or clinical use that satisfies patentability requirements.

Does US 4,216,211 create current generic-entry risk?

No. The patent’s expiration eliminates direct infringement risk based on claims 1 through 5.

A generic manufacturer could not receive a valid current patent-enforcement threat based solely on this patent. The same conclusion applies whether the manufacturer uses:

Etidronate disodium;
Another salt of etidronic acid;
Methanediphosphonic acid;
Methanedichlorodiphosphonic acid; or
Another organophosphonate falling within the expired genus.

The commercial analysis changes only if a later, unexpired patent covers a particular product, formulation, process, or indication.

Generic launch scenarios

Scenario	Risk from US 4,216,211
Generic etidronate tablet	No current risk from this patent
Generic etidronate injection	No current risk from this patent
New 2,3-DPG indication for etidronate	No current risk from this patent
New organophosphonate product	No current risk from this patent
New formulation or controlled-release product	Risk depends on later patents
New manufacturing process	Risk depends on later process patents
Combination therapy	Risk depends on later combination patents

What is the Orange Book status of US Patent 4,216,211?

US 4,216,211 is not a current Orange Book patent barrier.

The patent claims a method of increasing blood 2,3-DPG. It does not claim an approved drug composition, a drug substance, or a formulation in the conventional Orange Book sense. Method-of-use patents can be listed for approved products when they meet FDA listing requirements, but an expired patent has no continuing exclusivity effect.[3]

Etidronate products have historically been associated with the Didronel product and generic etidronate products. Didronel was approved for conditions including Paget’s disease of bone and prevention of heterotopic ossification, not as a general 2,3-DPG-elevating therapy.[4]

The key distinction is:

Issue	Effect
Patent covers 2,3-DPG use	Historical use patent
Patent expiration	Removes enforceable U.S. exclusivity
Orange Book listing	Cannot create current exclusivity after expiration
Approved etidronate indications	Separate from the claimed 2,3-DPG use
New 2,3-DPG indication	Could require separate FDA approval

Does the patent have FDA regulatory exclusivity?

No current FDA regulatory exclusivity follows from US 4,216,211.

Patent rights and FDA exclusivity are separate. The patent’s expiration does not determine whether an active ingredient has an approved NDA, and an NDA does not revive an expired patent.

For an etidronate product, a sponsor would need to address:

The applicable abbreviated or full NDA pathway;
Bioequivalence for a generic product;
Safety and efficacy for any new 2,3-DPG indication;
Labeling requirements;
Clinical evidence supporting the proposed blood-level effect; and
Any current patents listed for the relevant reference product.

A small-molecule organophosphonate is not a biologic. Biosimilar regulation under the Biologics Price Competition and Innovation Act is therefore not the relevant pathway.

Are there Paragraph IV challenges to US 4,216,211?

No current Paragraph IV challenge can target this patent because it expired in 1997.

Paragraph IV certifications concern patents listed for an approved reference drug and assert that the patent is invalid, unenforceable, or will not be infringed. An expired patent cannot provide a current period of patent-based generic delay or a valid basis for prospective patent enforcement.[5]

Historical litigation, if any, would not change the present legal position. The patent’s expiration extinguishes the remaining exclusionary right regardless of whether a prior dispute occurred.

What patent litigation affects organophosphonate products?

US 4,216,211 does not create current litigation exposure. The principal litigation questions for a modern organophosphonate product would concern later rights covering:

Salt selection;
Crystal or polymorphic forms;
Oral or injectable formulations;
Modified-release dosage forms;
Manufacturing and purification;
Combination treatment;
Dosing schedules;
Patient-selection criteria;
A new 2,3-DPG-related clinical indication; and
Device or delivery technology.

An expired genus patent can still appear in prior-art searches, invalidity analyses, freedom-to-operate opinions, and prosecution histories. It cannot independently block commercialization.

How strong was the patent estate for the claimed therapy?

The patent had meaningful breadth at issuance because claim 1 combined a large chemical genus with a functional therapeutic result. Claims 2 through 5 provided fallback positions for named compounds and salt or ester forms.

Its historical strengths included:

Broad coverage of vicinal and geminal organophosphonates;
Coverage of humans and lower animals;
Inclusion of pharmaceutically acceptable salts;
Functional coverage tied to increased blood 2,3-DPG;
Species claims for etidronic acid and methanediphosphonic compounds.

Its limitations included:

Dependence on the structural formula;
The requirement that the subject be in need of treatment;
The need to show that administration was sufficient to increase blood 2,3-DPG;
Potential enablement and written-description questions for a large Markush genus;
Method-of-treatment rather than composition-of-matter coverage;
No continuing term after 1997.

Because the formula appears in the supplied claim text as STR4 and STR5, the precise atom-by-atom boundaries of the vicinal and geminal structures cannot be reconstructed from the text alone. The legal analysis should therefore treat the claims as quoted while recognizing that definitive claim construction depends on the issued patent drawings, specification, prosecution history, and any relevant court interpretation.

What licensing or settlement value remains?

The patent has no current standalone licensing value as an exclusionary U.S. right.

A license could still have historical, evidentiary, or portfolio value if:

A foreign counterpart remains relevant in a jurisdiction with a different term;
The patent is included in a broader know-how package;
The patent holder owns later patents;
The transaction concerns historical liability or releases; or
The patent’s disclosure supports a commercial development program.

No current U.S. settlement is needed to authorize practice of claims 1 through 5. Any modern agreement should focus on later patents, regulatory rights, trade secrets, manufacturing know-how, trademarks, or commercial rights rather than US 4,216,211 itself.

How does this patent compare with modern organophosphonate patent strategies?

Patent strategy	US 4,216,211	Modern strategy
Core protection	Method of increasing 2,3-DPG	Composition, formulation, method, and patient selection
Chemical scope	Broad Markush organophosphonates	Often a defined molecule or narrowly characterized form
Formulation protection	Not apparent from the listed claims	Oral, injectable, depot, or controlled-release systems
Regulatory linkage	Historical use claim	Orange Book-listed product or method claims
Biosimilar relevance	None	Relevant only to biologic products
Current enforceability	Expired	Depends on later filing and expiration dates
Commercial value	Prior art and historical disclosure	Potentially active exclusivity

Key takeaways

US Patent 4,216,211 claims administration of defined organophosphonates to increase blood 2,3-DPG.
Claim 1 is a broad chemical-genus and method-of-treatment claim.
Claims 2 and 3 specifically target etidronic acid and sodium etidronate.
Claims 4 and 5 cover methanediphosphonic and methanedichlorodiphosphonic acids.
The patent issued August 5, 1980, and expired August 5, 1997.
It creates no current U.S. patent barrier, Paragraph IV risk, or FDA exclusivity.
Etidronate is a small-molecule bisphosphonate, so biosimilar rules do not apply.
Current freedom-to-operate analysis must focus on later formulation, manufacturing, dosing, combination, and method-of-use patents.
The precise scope of claim 1 depends on the original structural drawings and specification because the supplied text substitutes STR4 and STR5 for the chemical formulas.

FAQs about US Patent 4,216,211

Can a company market etidronate for a 2,3-DPG indication today?

US 4,216,211 does not prevent that activity because it expired in 1997. FDA approval, labeling, clinical evidence, and any later patent rights would remain separate issues.

Does claim 3 cover all uses of etidronate disodium?

No. Claim 3 is directed to use of sodium etidronate to increase blood 2,3-DPG. It is not a general composition claim covering every use of etidronate disodium.

Could a new organophosphonate be patented despite US 4,216,211?

Possibly, if the compound, formulation, method, or manufacturing process is patentably distinct over the expired disclosure and other prior art. The expired patent would remain relevant prior art.

Is 2,3-DPG the same as 2,3-BPG?

Yes. 2,3-DPG and 2,3-BPG are common names for 2,3-diphosphoglycerate and 2,3-bisphosphoglycerate, respectively.

Does expiration of the patent prove that etidronate is FDA-approved for increasing 2,3-DPG?

No. Patent expiration and FDA approval are separate legal and regulatory questions. The patent’s claimed use is not equivalent to an approved indication.

References

United States Patent No. 4,216,211. (1980). Method for increasing 2,3-diphosphoglycerate levels in blood. United States Patent and Trademark Office.
United States Code, 35 U.S.C. § 154. (2024). Contents and term of patent; provisional rights.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
U.S. Food and Drug Administration. (2024). Didronel: Etidronate disodium prescribing information.
United States Code, 21 U.S.C. § 355(j)(2)(A)(vii)(IV). (2024). Abbreviated applications and Paragraph IV certifications.

Details for Patent: 4,216,211

Summary for Patent: 4,216,211