United States Patent 4,868,179: Scope, Claims, Expiration, and Hydralazine-Isosorbide Dinitrate Patent Landscape

U.S. Patent No. 4,868,179 covered a mortality-reduction treatment for chronic congestive heart failure using combined oral hydralazine and isosorbide dinitrate. It issued on September 19, 1989, and its ordinary 17-year patent term expired on September 19, 2006. The patent no longer creates an enforceable U.S. exclusion right, but it remains important as the foundational patent for the hydralazine-isosorbide dinitrate heart-failure regimen later commercialized as BiDil.[1]

The claims are method-of-treatment claims. They do not require a particular tablet, capsule, fixed-dose ratio, manufacturer, or patient race. They require administration of both active ingredients within specified daily dosage ranges to a defined heart-failure population.

What does U.S. Patent 4,868,179 protect?

The patent protects the oral administration of:

Component	Claimed daily amount
Hydralazine, or an acid-addition salt	About 75 to about 300 mg
Isosorbide dinitrate	About 40 to about 160 mg

The regimen must be used in a patient who has:

Chronic congestive heart failure;
Impaired cardiac function;
Reduced exercise tolerance; and
A need for treatment intended to reduce mortality associated with the condition.

Claim 2 adds background or concomitant therapy:

Digoxin sufficient to produce a serum concentration of at least about 0.7 ng/mL; and
An effective edema-managing amount of a specified diuretic.

The listed diuretics are thiazides, ethacrynic acid, furosemide, spironolactone, and triamterene.[1]

How broad is claim 1?

Claim 1 is broader than the commercial BiDil product in several material respects.

Claim 1 does not require a fixed-dose combination

The claim covers administering hydralazine and isosorbide dinitrate as separate products, provided that both are administered orally and the aggregate daily doses fall within the claimed ranges. A single tablet is not required.

This distinction matters because the patent is directed to a therapeutic combination, not exclusively to a particular pharmaceutical composition.

Claim 1 does not require simultaneous administration

The claim does not expressly require the two agents to be taken at the same time. The ordinary infringement analysis would focus on whether the accused regimen administers both agents as part of the claimed treatment method and within the specified daily amounts.

A regimen using separate morning and evening administrations could fall within the language if the treatment is understood as administration of the claimed combination.

The hydralazine range is relatively wide

The hydralazine limitation spans approximately fourfold:

Lower boundary: 75 mg per day;
Upper boundary: 300 mg per day.

The isosorbide dinitrate limitation also spans fourfold:

Lower boundary: 40 mg per day;
Upper boundary: 160 mg per day.

The use of “about” introduces a factual boundary question around the numerical endpoints. It does not eliminate the requirement that the daily doses be reasonably within the claimed ranges.

The claim is not limited to Black patients

Claim 1 contains no racial or ethnic limitation. It is directed to a general chronic heart-failure population with impaired cardiac function and reduced exercise tolerance.

This differs from the later BiDil regulatory and patent position, which focused on treatment of self-identified Black patients with heart failure. The demographic limitation associated with BiDil arose from later clinical development, labeling, and patenting rather than from claim 1 of the ’179 patent.[2]

What does claim 2 add?

Claim 2 narrows claim 1 by requiring additional standard heart-failure therapy.

Digoxin concentration requirement

The patient must receive enough digoxin to achieve a serum concentration of at least approximately 0.7 ng/mL. This is a measurable pharmacokinetic limitation, not merely a requirement that digoxin be prescribed.

Potential proof issues would include:

The patient’s actual serum digoxin level;
The timing of the blood sample;
Whether the measured concentration was achieved during the alleged treatment period;
Whether the concentration was attributable to the administered digoxin regimen.

A patient receiving digoxin without a documented level of at least about 0.7 ng/mL may not satisfy this limitation.

Diuretic requirement

The claim requires an effective edema-managing amount of one of the named diuretics. The requirement is functional rather than numerically fixed. The relevant question is whether the amount was effective for managing edema in the treated patient.

The claim does not cover every possible diuretic. The listed group is closed in form, although “thiazides” is a drug-class category rather than a single compound.

Which products fall within the claimed dose ranges?

The FDA-approved BiDil strength is 20 mg isosorbide dinitrate and 37.5 mg hydralazine per tablet. The labeled regimen is two tablets three times daily, producing:

Daily exposure	BiDil labeled regimen	Claim 1 range
Hydralazine	225 mg/day	75-300 mg/day
Isosorbide dinitrate	120 mg/day	40-160 mg/day

The labeled BiDil regimen therefore falls directly within the numerical dosage ranges of claim 1.[2]

Other regimens could also fall within the claim. Examples include:

75 mg hydralazine plus 40 mg isosorbide dinitrate daily;
150 mg hydralazine plus 80 mg isosorbide dinitrate daily;
300 mg hydralazine plus 160 mg isosorbide dinitrate daily.

The two drugs do not need to be administered in the same ratio as BiDil.

When did U.S. Patent 4,868,179 expire?

U.S. Patent 4,868,179 issued on September 19, 1989. Because it is a pre-June 8, 1995 patent, its ordinary term was 17 years from issuance under the transition rules governing pre-1995 patents. Its ordinary expiration date was September 19, 2006.[1][3]

Event	Date
Patent issued	September 19, 1989
Ordinary 17-year expiration	September 19, 2006
Current enforceable patent term	Expired

The patent cannot support a present U.S. infringement action or a current Paragraph IV challenge. A generic applicant today does not need to certify that the ’179 patent is invalid or not infringed because the patent has expired.

What was the relationship between the patent and BiDil?

BiDil is a fixed-dose combination of hydralazine hydrochloride and isosorbide dinitrate. The FDA approved BiDil in June 2005 under NDA 20-727 for use in combination with standard therapy in the treatment of heart failure in self-identified Black patients.[2]

The ’179 patent was foundational because its central regimen corresponds to the pharmacologic combination and dosage pattern used in BiDil. Its expiration, however, occurred shortly after BiDil approval.

The commercial exclusivity strategy therefore depended more heavily on later patents and regulatory exclusivity than on the remaining life of the ’179 patent. Later BiDil-related patent claims addressed narrower subject matter, including patient populations, therapeutic use, and product-specific aspects of the combination.[4]

What was the clinical basis for the patent?

The patent reflected clinical work evaluating vasodilator treatment in chronic heart failure. Hydralazine reduces arterial vascular resistance, while isosorbide dinitrate reduces venous return and cardiac preload. Their combined hemodynamic effects differ from treatment with either agent alone.

The V-HeFT-I trial compared hydralazine-isosorbide dinitrate, prazosin, and placebo in patients receiving background therapy that commonly included digoxin and diuretics. The trial reported a mortality benefit for the hydralazine-isosorbide dinitrate arm compared with placebo during follow-up.[5]

The patent converted that clinical finding into a dosage-defined method claim. The core inventive proposition was not merely symptom relief or hemodynamic improvement. It was reduction in mortality associated with chronic congestive heart failure through the specified combination.

What are the principal claim-construction issues?

“Reducing the incidence of mortality”

The claim is framed as a therapeutic method with a mortality-reduction objective. It does not require that an individual patient survive longer or avoid death. Method claims using this type of language generally focus on whether the treatment was administered with the claimed therapeutic purpose and in the claimed patient population.

“Impaired cardiac function”

This limitation identifies a disease state but does not provide a numerical ejection-fraction threshold in the quoted claim. Clinical records, diagnosis, cardiac testing, and treatment history would be relevant to determining whether the limitation is met.

“Reduced exercise tolerance”

This is a functional patient limitation. It is broader than a specific New York Heart Association class designation, although NYHA functional status, exercise testing, and clinical notes could be relevant evidence.

“Combination”

The combination requirement is satisfied only if both hydralazine and isosorbide dinitrate are administered. Administration of hydralazine alone, isosorbide dinitrate alone, or another nitrate would not satisfy claim 1.

“Per day”

The claim is written around daily dosage. A product label or tablet strength alone would not establish infringement. The relevant exposure is the patient’s administered daily amount.

What patents followed the ’179 patent?

The later U.S. BiDil estate generally pursued narrower protection than the ’179 patent. The relevant categories included:

Patent category	Typical protected subject matter	Relationship to ’179
Combination-use patents	Hydralazine plus isosorbide dinitrate for heart failure	Narrower patient or treatment restrictions
Patient-population patents	Use in self-identified Black patients	Added a demographic limitation absent from ’179
Product or formulation patents	Fixed-dose hydralazine-isosorbide dinitrate dosage forms	More specific than the method claims in ’179
Regulatory exclusivity	FDA approval-based exclusivity for the approved indication	Separate from patent term
Manufacturing and formulation know-how	Tablet production, stability, dissolution, and scale-up	May create practical barriers without extending ’179

U.S. Patent No. 6,784,187 is commonly associated with the later BiDil patent position and was directed to treatment of heart failure in Black patients using hydralazine and isosorbide dinitrate.[4] That patent was materially narrower than claim 1 of the ’179 patent because it incorporated a patient-population limitation.

Patent-family analysis must separate three concepts:

The expired broad combination method in the ’179 patent;
Later active or formerly active BiDil-specific patents; and
Unpatented regulatory, manufacturing, and commercial know-how.

What was the Orange Book status of the ’179 patent?

The ’179 patent could not create a current Orange Book barrier after its September 2006 expiration. FDA patent-listing consequences are distinct from patent validity and infringement, but an expired patent cannot support a current 30-month stay based on a Paragraph IV certification.[3][6]

For BiDil, the commercially relevant Orange Book analysis historically centered on later patents listed for the approved product and indication. A generic applicant evaluating BiDil would need to review the Orange Book listing in effect on the ANDA filing date, identify each unexpired listed patent, and determine whether a Paragraph IV certification or section viii statement was appropriate.

The expired ’179 patent would not independently delay approval of a present-day ANDA.

Were there Paragraph IV challenges to the ’179 patent?

A Paragraph IV certification is relevant only while a listed patent remains unexpired. Because the ’179 patent expired in 2006, it is no longer the subject of a viable current Paragraph IV certification.

The key generic challenge risk historically shifted to later BiDil patents. Those patents could generate:

Paragraph IV litigation;
A 30-month FDA approval stay;
Patent-certification disputes;
Settlement agreements; and
Potentially delayed generic launch.

The ’179 patent itself no longer creates launch risk. Any current BiDil patent risk must be assessed against the surviving Orange Book entries and their expiration dates, not against the expired foundational patent.

What generic entry risks remain?

Formulation substitution risk

A generic manufacturer could seek approval for the same active ingredients without relying on the ’179 patent. The primary issues would include pharmaceutical equivalence, bioequivalence, dosage strength, labeling, and any remaining listed patents.

Method-of-use risk

If a later patent claims a specific heart-failure population or indication, a generic applicant may use a section viii statement to omit the patented use, provided the proposed labeling does not encourage the patented method.

Combination-product risk

Hydralazine and isosorbide dinitrate are both old active ingredients. The main historical barrier was the approved combination and its clinical-use positioning, not new chemical entity protection.

Manufacturing risk

Manufacturing barriers are likely to involve:

Fixed-dose tablet uniformity;
Stability of the two active ingredients;
Dissolution performance;
Taste and tablet tolerability;
Scale-up reproducibility; and
Regulatory comparability.

These barriers may increase development cost but do not restore exclusivity to the expired ’179 patent.

How strong was the patent estate?

The ’179 patent was commercially strong during its term because it covered the central therapeutic combination across a broad patient population and did not require the later BiDil racial limitation. Its weaknesses were structural:

The active ingredients were old;
The claims were method claims rather than composition-of-matter claims;
The patent expired in 2006;
The dosage ranges were broad but clinically recognizable;
The invention depended on treatment-purpose and patient-condition limitations.

The later estate had narrower claim scope but greater relevance after BiDil approval. Its strength depended on whether a generic product’s label, dosing, formulation, and target population practiced the specific later claims.

What licensing and commercial issues affected the patent landscape?

The hydralazine-isosorbide dinitrate program involved academic clinical research, University of Minnesota-related intellectual property, and subsequent commercial development by NitroMed. BiDil was later commercialized through licensing and commercial arrangements involving the patent holders and product sponsor.[2][4]

The commercial value of the ’179 patent was therefore tied to:

Exclusive licensing;
FDA approval of BiDil;
Later patent filings;
Reimbursement and market access;
Physician adoption;
The ability to distinguish the branded fixed-dose product from separate generic components.

Once the ’179 patent expired, licensing of that patent could no longer prevent independent use of the claimed regimen in the United States.

What is the competitive landscape for hydralazine and isosorbide dinitrate?

The relevant competitive products and treatment approaches include:

Treatment	Patent position	Clinical or commercial role
BiDil	Later product and use patents historically important; ’179 expired	Fixed-dose combination
Generic hydralazine	Old active ingredient; no ’179 barrier	Separate vasodilator
Generic isosorbide dinitrate	Old active ingredient; no ’179 barrier	Separate nitrate
Separate hydralazine plus isosorbide dinitrate	Covered by ’179 during its term; now unblocked by that patent	Therapeutic substitute for fixed-dose product
ACE inhibitors, ARBs, ARNIs, beta blockers, and mineralocorticoid antagonists	Separate patent and regulatory histories	Standard heart-failure competitors

The practical substitution threat to BiDil has always come from separate generic hydralazine and isosorbide dinitrate, even where those products are not therapeutically interchangeable in every regulatory or prescribing context.

Key Takeaways

U.S. Patent 4,868,179 covered oral hydralazine plus isosorbide dinitrate for mortality reduction in chronic congestive heart failure.
Claim 1 requires approximately 75-300 mg/day of hydralazine and 40-160 mg/day of isosorbide dinitrate.
Claim 2 adds digoxin at a serum concentration of at least approximately 0.7 ng/mL and an effective dose of a specified diuretic.
The claims do not require a fixed-dose tablet, simultaneous administration, or treatment of Black patients.
BiDil’s labeled regimen of 225 mg/day hydralazine and 120 mg/day isosorbide dinitrate falls within claim 1.
The patent issued September 19, 1989, and expired September 19, 2006.
The ’179 patent cannot support a current U.S. infringement claim, Paragraph IV delay, or generic-launch block.
Later BiDil patents narrowed the field through patient-population, formulation, and product-specific claims.
Current competitive risk comes from later listed patents, regulatory requirements, and commercial substitution by generic components, not from the expired ’179 patent.

FAQs

Can separate generic hydralazine and isosorbide dinitrate infringe U.S. Patent 4,868,179 today?

No. The patent expired on September 19, 2006. Separate generic products may be used without creating current infringement liability under the ’179 patent.

Did Patent 4,868,179 cover BiDil specifically?

It covered the therapeutic regimen embodied by BiDil’s labeled dosage, but it did not require the BiDil tablet, its 20 mg/37.5 mg strength, or the later Black-patient indication.

Is a digoxin serum level required for infringement of claim 1?

No. The digoxin and diuretic requirements appear in claim 2. Claim 1 does not require digoxin or a diuretic.

Does claim 2 cover any edema treatment?

No. Claim 2 identifies particular diuretic categories and requires an effective edema-managing amount. It does not cover every edema treatment.

Can the expired patent be used to challenge a later BiDil patent?

No. Expired prior patents may be relevant as prior art in assessing validity, but the ’179 patent itself cannot be enforced against later products and does not eliminate the need to analyze later patent claims independently.

References

U.S. Patent No. 4,868,179, Method of treating congestive heart failure (issued Sept. 19, 1989).
U.S. Food and Drug Administration. (2005). BiDil prescribing information and approval materials. NDA 20-727.
35 U.S.C. § 154. Patent term and transition provisions for pre-June 8, 1995 patents.
U.S. Patent No. 6,784,187, Method of treating heart failure in a Black patient (issued Aug. 31, 2004).
Cohn, J. N., Archibald, D. G., Ziesche, S., et al. (1986). Effect of vasodilator therapy on mortality in chronic congestive heart failure. New England Journal of Medicine, 314(24), 1547-1552.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Canada	1308659	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 4,868,179