US Drug Patent 4,761,418: Mivacurium Chloride Claims, Scope, Expiration, and Patent Landscape

US Patent 4,761,418 covers mivacurium-type bis-quaternary tetrahydroisoquinolinium compounds, including specified E- and Z-configured octenedioyl-linked compounds, their pharmaceutically acceptable salts, sterile injectable compositions, and parenteral muscle-relaxant use. The patent was granted on August 2, 1988, and, under the pre-1995 patent-term regime, expired no later than August 2, 2005, absent an extraordinary term adjustment or enforceable extension. It therefore presents no current US composition, formulation, or method-of-use barrier.

The principal commercial product associated with the claimed chemistry is mivacurium chloride, marketed as Mivacron, a short-acting nondepolarizing neuromuscular blocking agent. FDA approved Mivacron in 1992 under NDA 019998. The relevant risk today is regulatory and commercial substitution, not infringement of US Patent 4,761,418.

What drug does US Patent 4,761,418 cover?

US 4,761,418 covers mivacurium and stereochemically related bis-benzylisoquinolinium compounds.

The claimed molecular architecture contains:

Two tetrahydroisoquinolinium units.
6,7-dimethoxy substitution on each isoquinoline ring.
A 3,4,5-trimethoxybenzyl substituent on each nitrogen-containing ring system.
Two quaternary ammonium centers.
An octenedioyl-linked bis-oxytrimethylene bridge.
Defined E or Z alkene geometry.
Defined relative and absolute stereochemistry.
Chloride and other pharmaceutically acceptable counterions.

Mivacurium chloride is a mixture of stereoisomeric bis-quaternary ammonium compounds. The patent’s claims reflect that stereochemical complexity by covering racemic or mixed forms, individual stereoisomeric configurations, and dichloride salts.

What is the pharmacological product?

Mivacurium chloride is an intravenous, short-acting, nondepolarizing neuromuscular blocker. It produces skeletal-muscle paralysis by competitively blocking acetylcholine at the neuromuscular junction. The FDA label identifies the product for use as an adjunct to general anesthesia, for tracheal intubation, and to provide skeletal-muscle relaxation during surgery or mechanical ventilation (FDA, 1992).

The product is administered parenterally because the permanently charged bis-quaternary structure substantially limits oral absorption.

How many patents cover mivacurium under US 4,761,418?

One US patent is directly represented by the supplied claims: US 4,761,418. Its claim set has three layers:

Claim group	Claims	Subject matter	Practical scope
Composition claims	1-12	Mivacurium-related cations, salts, stereoisomers, and dichlorides	Core molecular protection
Therapeutic-use claims	13, 15	Parenteral administration to produce muscle relaxation	Method-of-use protection
Formulation claim	14	Sterile composition with solvent	Injectable formulation protection

The patent is not limited to a single named product presentation. It covers the active chemical entity in several ionic and stereochemical forms, as well as sterile compositions containing one or more claimed compounds.

What chemical structures are protected by the composition claims?

Claims 1 and 2: broad cation and dichloride forms

Claim 1 covers the specified E-configured bis-quaternary cation associated with a pharmaceutically acceptable anion. This is the broadest salt-oriented claim in the set because the anion is not restricted to chloride.

Claim 2 narrows the subject matter to the corresponding dichloride salt. For a dicationic molecule, the dichloride form is the expected neutral salt representation.

The distinction is commercially relevant. A product containing the same cation with a different pharmaceutically acceptable counterion could fall within claim 1 even if it did not meet claim 2.

Claims 3 and 4: Z-configured compounds

Claims 3 and 4 address the Z-configured octenedioyl-linked compounds and their dichlorides. They extend the patent beyond the E alkene geometry recited in claims 1 and 2.

The supplied text uses “(Z)-4-Octenedioyl” in claims 3 and 4 but uses “(E)” in the first group. Alkene geometry is a material limitation. A compound with the wrong configuration would not satisfy the literal configuration requirement, subject to claim-construction principles and any applicable equivalents analysis.

Claims 5 through 12: stereochemical variants

Claims 5 through 12 define individual or partially defined stereochemical configurations at the chiral centers.

The principal stereochemical categories are:

(1R,1'R) configuration.
(1R,1'R,2R,2'R) configuration.
(1R,1'R,2R,2'S) configuration.
(1R,1'R,2S,2'S) configuration.

These claims are narrower than the general cation claim because they specify absolute or relative configurations. They can protect individual stereoisomers even where a broader commercial product is supplied as a mixture.

Claim-language defects and apparent transcription issues

Several supplied claims contain wording that would require review against the certified patent text before being used in litigation or freedom-to-operate analysis:

Claim 6 states “1,2,4,3-tetrahydro,” which appears to be a sequencing or transcription error for “1,2,3,4-tetrahydro.”
Claim 10 refers to a “chloride” even though the compound is dicationic and the corresponding salt would ordinarily require two chloride anions.
Claim 11 refers to a “dication in association with a pharmaceutically acceptable anion,” which is chemically imprecise unless the claim is read as covering the salt system generally.
Claims 3 and 4 contain extra parentheses and inconsistent nomenclature.
Claim 1 uses “cation in association with” an anion, while other claims specify dichloride.

These issues do not revive the patent or create current exclusivity. They matter only for historical claim interpretation, prosecution-history analysis, or litigation involving conduct before expiration.

What formulations are protected by US 4,761,418?

Claim 14 covers a sterile pharmaceutical composition containing one or more claimed compounds in an effective muscle-relaxant amount and a pharmaceutically acceptable solvent.

The formulation claim has four principal limitations:

The composition must be sterile.
It must contain at least one compound covered by claims 1 through 12.
The compound must be present in an effective muscle-relaxant amount.
The composition must contain a pharmaceutically acceptable solvent.

The claim does not recite a particular concentration, vial size, buffer, preservative, pH, infusion system, or dosing schedule in the supplied text. Its scope is therefore broader than a narrowly defined commercial formulation, but it remains dependent on inclusion of a covered active compound.

For an injectable product, the practical formulation requirements would include sterility, suitable solvent compatibility, chemical stability, container closure integrity, and acceptable intravenous administration characteristics. Those regulatory requirements are separate from the patent claim.

What method-of-use protection does the patent provide?

Claims 13 and 15 cover parenteral administration of the claimed compounds to produce muscle relaxation in a mammal.

Claim	Covered compounds	Administration	Therapeutic result
13	Claims 1, 3, or 5 compounds	Parenteral	Muscle relaxation
15	Claims 9, 10, 11, or 12 compounds	Parenteral	Muscle relaxation

The method claims are narrower than a general medical-use claim because they require:

A mammalian subject.
Parenteral administration.
An effective muscle-relaxant amount.
The specified claimed compound or compound group.

They do not expressly require general anesthesia, intubation, surgery, mechanical ventilation, or a particular dosing regimen. The FDA-approved Mivacron uses fall within the broad clinical context of neuromuscular blockade described in the label, but the patent’s method language is not coextensive with every modern labeling limitation.

When did US Patent 4,761,418 lose exclusivity?

US Patent 4,761,418 expired in 2005.

Event	Date or period
US patent grant	August 2, 1988
Applicable US term regime	Pre-June 8, 1995, generally 17 years from grant
Expected basic expiration	August 2, 2005
Current enforceability	None after expiration
Current Paragraph IV significance	None for this expired patent

Patent term adjustment and patent term extension rules differ depending on filing date, grant date, regulatory review, and statutory eligibility. The basic 17-year term from grant governs this patent absent a recorded extension or adjustment. The Orange Book and FDA regulatory records should be read together for any historical listing analysis (USPTO, 1988; 35 U.S.C. § 154).

There is no current US exclusivity attributable to this patent. Any current market protection would have to arise from another unexpired patent, regulatory exclusivity, supply restrictions, manufacturing complexity, or commercial factors.

What is the Orange Book status of mivacurium chloride?

Mivacurium chloride was approved by FDA under NDA 019998 for Mivacron. Historically, US Patent 4,761,418 was the key composition patent associated with the product’s active ingredient.

The relevant Orange Book conclusions are:

Mivacurium chloride is a small-molecule drug, not a biologic.
Biosimilar rules do not apply.
A generic applicant would use an ANDA, not a biosimilar application.
The patent’s expiration eliminates any current Orange Book patent barrier based on US 4,761,418.
Any historical listing under the NDA would have no continuing exclusionary effect after expiration.
A current generic applicant would need to address only patents and exclusivities that remain legally active at the time of filing.

FDA’s Orange Book framework lists patents and regulatory exclusivities associated with approved drug products. Listed-patent status is not itself a determination that a patent is valid or infringed. Expiration ends enforceability even if the product remains identified in historical regulatory records (FDA, 2025).

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

A Paragraph IV certification would have been relevant only while US 4,761,418 remained unexpired and listed for the applicable NDA. After August 2, 2005, the patent could not support a 30-month stay or an infringement action based solely on a later ANDA filing.

The supplied record does not establish a particular Paragraph IV notice, district-court complaint, settlement agreement, or 180-day exclusivity award involving this patent. The current legal position is clear: no Paragraph IV challenge to an expired patent creates a present US launch block.

What settlement agreements matter?

No settlement agreement can be attributed to US 4,761,418 from the claim text alone. A historical settlement, if any, would have to be evaluated by:

Filing date of the ANDA.
Date of Paragraph IV notice.
Patent expiration date.
Any agreed launch date.
Whether the agreement included payment, supply, licensing, or manufacturing terms.
FTC or court review records.

A settlement could have affected market entry before 2005 but cannot extend the patent’s statutory enforceability beyond expiration.

How strong was the patent estate for mivacurium?

Historically, US 4,761,418 had meaningful composition-patent strength because it combined a distinctive molecular scaffold with stereochemical and salt limitations.

Strengths

Core chemical-entity claims covered the principal active structure.
Claim 1 reached pharmaceutically acceptable salts beyond chloride.
Claims 3 through 12 addressed multiple geometric and stereochemical variants.
Claim 14 covered sterile injectable compositions.
Claims 13 and 15 covered parenteral muscle-relaxant use.
The chemical structure is sufficiently specific to distinguish the claimed compounds from unrelated neuromuscular blockers.

Weaknesses

The claims depend heavily on exact nomenclature and stereochemical interpretation.
Several supplied claims contain apparent drafting or transcription inconsistencies.
Product claims could be attacked through anticipation or obviousness based on earlier bis-benzylisoquinolinium chemistry.
Method claims could face limitations based on the definition of the claimed compound, administration route, and effective amount.
The entire estate is expired.

The patent was stronger as a historical blocking patent than as a current commercial asset. Today, its residual value is primarily documentary: it identifies the original chemical and stereochemical disclosure relevant to generic development, process history, and freedom-to-operate review.

How does mivacurium compare with competing neuromuscular blockers?

Mivacurium competes with other injectable nondepolarizing neuromuscular blockers, including atracurium, cisatracurium, rocuronium, and vecuronium.

Drug	General class	Duration profile	Biosimilar pathway	US 4,761,418 relevance
Mivacurium chloride	Bis-quaternary benzylisoquinolinium	Short acting	Not applicable	Directly covered historically
Atracurium besylate	Benzylisoquinolinium	Intermediate	Not applicable	Not covered by these claims
Cisatracurium besylate	Atracurium stereoisomer	Intermediate	Not applicable	Not covered by these claims
Rocuronium bromide	Aminosteroid	Intermediate	Not applicable	Not covered by these claims
Vecuronium bromide	Aminosteroid	Intermediate	Not applicable	Not covered by these claims

Mivacurium’s commercial differentiation is its short duration and utility where relatively rapid recovery from neuromuscular blockade is desired. Its disadvantages include histamine-related reactions and dependence on plasma cholinesterase-mediated metabolism, which can prolong paralysis in susceptible patients. These clinical characteristics are independent of patent status (FDA, 1992).

What generic-entry risks exist for mivacurium chloride?

The patent risk is low because US 4,761,418 is expired. Generic-entry constraints are more likely to involve regulatory equivalence and manufacturing execution.

Generic development issues

An ANDA applicant would need to address:

Active ingredient identity and salt form.
Stereoisomeric composition.
Injectable concentration and dosage form.
Sterility and particulate controls.
Stability and degradation profile.
Container and closure compatibility.
Bioequivalence or applicable parenteral-product requirements.
Labeling consistency with the reference-listed drug.

Manufacturing and IP barriers

The molecule has a complex bis-quaternary structure and multiple stereocenters. Potential technical barriers include:

Control of E/Z alkene geometry.
Control of cis/trans and absolute stereochemistry.
Purification of closely related stereoisomers.
Reproducible quaternization.
Control of residual solvents and inorganic salts.
Stability during sterilization and storage.
Analytical methods capable of distinguishing stereoisomeric impurities.

These are manufacturing and quality barriers, not continuing rights under US 4,761,418. A later process patent could create a separate risk, but it would need to be identified independently from the expired composition patent.

What geographic coverage does the patent have?

US 4,761,418 provides US coverage only. Its legal effect does not extend to:

Canada.
Europe.
Japan.
China.
Australia.
Other jurisdictions.

The corresponding international landscape would depend on national counterparts, national-phase filings, prosecution outcomes, and expiration dates. Foreign patents based on the same priority disclosure could have expired on different dates, although patents filed in the same era generally have no meaningful current term in major markets.

For a multinational launch, US freedom to operate should not be treated as evidence of freedom to operate elsewhere.

What is the current commercial exposure of US 4,761,418?

Current direct revenue exposure is zero from an enforceable-patent perspective. The patent cannot collect royalties or support an injunction after expiration.

The historical commercial exposure was material because the claims covered:

The active pharmaceutical ingredient.
Alternative pharmaceutically acceptable salts.
Multiple stereochemical forms.
Sterile injectable compositions.
The principal muscle-relaxant use.

The patent’s post-expiration value may remain relevant to diligence involving:

Generic entry.
Acquisition of legacy neuromuscular-blocker products.
Historical licensing.
Product-development records.
Patent term and launch-date disputes.
Foreign counterpart review.
Manufacturing-route analysis.

Key Takeaways

US Patent 4,761,418 is the foundational US composition patent for mivacurium-type bis-quaternary benzylisoquinolinium muscle relaxants.
Claims 1 through 12 cover E/Z forms, salts, dichlorides, and defined stereoisomers.
Claim 14 covers sterile pharmaceutical compositions containing the claimed compounds.
Claims 13 and 15 cover parenteral administration for muscle relaxation.
Mivacurium chloride was marketed as Mivacron and approved under NDA 019998 in 1992.
The patent granted August 2, 1988, and expired approximately August 2, 2005.
It is a small-molecule patent; biosimilar rules do not apply.
No current Paragraph IV stay, injunction, or launch block can arise from this expired patent.
Current risk is concentrated in regulatory equivalence, stereochemical control, injectable manufacturing, and any later unexpired process or formulation rights.
The supplied claim text contains apparent nomenclature inconsistencies that should be distinguished from the certified patent record in any historical litigation analysis.

Frequently Asked Questions

Does US Patent 4,761,418 cover all mivacurium stereoisomers?

It covers the specifically recited E/Z and stereochemical forms, including broader cation and dichloride categories. Coverage depends on the exact configuration and certified claim language.

Is mivacurium chloride protected by a current US patent?

Not by US Patent 4,761,418. That patent expired in 2005.

Can a generic mivacurium applicant rely on an ANDA?

Yes. Mivacurium chloride is a small-molecule drug, so the relevant pathway is an ANDA referencing the applicable reference-listed drug.

Does the patent cover oral mivacurium?

The supplied method claims require parenteral administration. The composition claims are not expressly limited to an administration route, but the claimed sterile formulation is directed to pharmaceutical use and is particularly relevant to injectable products.

Are biosimilars relevant to mivacurium chloride?

No. Mivacurium chloride is a chemically synthesized small molecule, not a biologic subject to the biosimilar pathway.

Sources:

U.S. Patent No. 4,761,418. (1988). Bis-quaternary ammonium compounds. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (1992). Mivacron (mivacurium chloride injection) prescribing information. FDA.
U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Code. (2024). 35 U.S.C. § 154, patent term.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	8418303	Jul 18, 1984

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0181055	⤷ Start Trial	SPC/GB93/031	United Kingdom	⤷ Start Trial
European Patent Office	0181055	⤷ Start Trial	96C0001	Belgium	⤷ Start Trial
Austria	60759	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,761,418

Summary for Patent: 4,761,418