US Patent 5,677,331: Scope, Claims, Expiration, and Artemether-Lumefantrine Patent Landscape

US Patent 5,677,331 covers oral pharmaceutical compositions and treatment methods combining benflumetol, now generally called lumefantrine, with artemether for malaria. Its strongest commercial relevance was as an early patent covering the fixed-dose combination later marketed as Coartem and Riamet.

The patent’s core protection is narrow in ingredient identity but broad across dosage forms and excipients. Claims 1 through 4 cover compositions; claim 5 covers oral administration of the combination to treat malaria. The patent has expired under the ordinary US patent term and does not provide a current barrier to US generic or follow-on development.

What does US Patent 5,677,331 protect?

US 5,677,331 protects a fixed combination of:

Benflumetol, also known as lumefantrine
Artemether
Pharmaceutically acceptable additives
Oral administration to humans
Antimalarial use
Synergistic activity between the two active ingredients

The patent does not claim lumefantrine or artemether individually. It claims their combination and therapeutic use.

The patent issued on October 14, 1997, from an application filed in the United States in 1995. The patent was assigned to Ciba-Geigy AG, which became part of Novartis through corporate consolidation. The commercial product associated with the invention is artemether/lumefantrine, marketed in the United States as Coartem.

Claim architecture

Claim	Type	Principal limitation
1	Composition	Oral human pharmaceutical composition containing synergistic amounts of benflumetol and artemether with acceptable additives
2	Composition	Benflumetol-to-artemether weight ratio of 1:1 to 10:1
3	Composition	Benflumetol-to-artemether weight ratio of 3:1 to 7:1
4	Composition	Benflumetol-to-artemether weight ratio of 5:1 to 6:1
5	Method of treatment	Oral administration of synergistic amounts of benflumetol and artemether to a human with malaria

The dependent claims narrow the ratio progressively. Claim 4 is the narrowest composition claim and most closely tracks the commercial 6:1 strength ratio used in Coartem tablets.

How broad is claim 1 of US 5,677,331?

Claim 1 is broad in formulation terms but narrow in active-ingredient terms.

A potentially infringing product would generally need to contain:

Both lumefantrine and artemether.
A pharmaceutical composition intended for oral administration.
Amounts that are antimalarially effective and synergistic.
Pharmaceutically acceptable additives.
Use in humans.

The claim does not require a tablet, a particular dissolution profile, a specific excipient, a particular particle size, or a defined manufacturing process. It could therefore reach multiple oral dosage forms, including tablets, capsules, powders, granules, and oral suspensions, provided the product satisfies the active-ingredient and pharmaceutical-composition limitations.

The claim is limited by the word "consists." That closed transition generally excludes additional active pharmaceutical ingredients from the claimed composition, although ordinary excipients and additives remain permitted under the claim language. A product containing a third antimalarial active ingredient could have a non-infringement position based on the closed composition language, subject to the full claim construction and the doctrine of equivalents.

What does "synergistic" require?

"Synergistic" is a material limitation. The patent describes the combination as producing greater antimalarial activity than would be expected from simply adding the separate effects of the two compounds.

A patent dispute would likely focus on:

The meaning of synergy in the claim;
Whether synergy must be demonstrated in vitro, in vivo, or clinically;
The relevant parasite species and strains;
The tested dose ratio;
Whether the claimed product must show synergy at the time of manufacture or only be capable of producing it.

A generic manufacturer could challenge the limitation by arguing that its product has the same ingredients but does not satisfy the claimed synergistic relationship. The patent holder could respond that the claimed ratio and pharmacological characteristics inherently produce the required effect.

What ratios are protected by US 5,677,331?

The patent creates a nested ratio structure.

Ratio range	Claim	Practical significance
1:1 through 10:1 lumefantrine:artemether	2	Broad ratio subrange
3:1 through 7:1	3	Intermediate ratio range
5:1 through 6:1	4	Narrowest claimed range
No express ratio	1 and 5	Still require a synergistic combination

The commercial Coartem formulation uses 120 mg lumefantrine and 20 mg artemether per tablet, a 6:1 weight ratio. A standard six-tablet adult treatment course therefore contains 720 mg of lumefantrine and 120 mg of artemether.

The ratio claims are composition claims. Claim 5 does not expressly reproduce the 1:1 to 10:1 limitations, although it requires a synergistic amount of both compounds. That distinction creates a potentially broader method-of-treatment scope than the dependent composition claims.

When did US Patent 5,677,331 expire?

The patent’s ordinary US term expired in approximately 2015, based on the 20-year term measured from the relevant US nonprovisional filing date. The patent therefore does not currently block manufacture, sale, or FDA approval of an otherwise lawful generic artemether/lumefantrine product in the United States.

Event	Date or period
US application filing	1995
Patent issuance	October 14, 1997
Ordinary 20-year patent term	Approximately 2015
Current status	Expired

The patent’s expiration removed the principal early composition patent barrier. Any current freedom-to-operate review must focus on later patents, regulatory exclusivity, trademarks, manufacturing know-how, and product-specific patents rather than on US 5,677,331 itself.

What FDA regulatory status is associated with the patent?

The combination was approved by the FDA as Coartem under NDA 022268 on April 8, 2009. Coartem contains artemether and lumefantrine and is indicated for the treatment of acute, uncomplicated malaria caused by Plasmodium falciparum in adults and children weighing at least 5 kg.[1]

The product was approved under the standard NDA pathway, not the biologics licensing pathway. Biosimilar regulation is therefore irrelevant. Follow-on products would generally proceed through an abbreviated new drug application, subject to FDA requirements for pharmaceutical equivalence, bioequivalence, labeling, and manufacturing quality.

FDA exclusivity versus patent protection

FDA exclusivity and patent protection are separate rights.

US 5,677,331 provided patent exclusivity and has expired.
Coartem’s 2009 approval could have carried statutory regulatory exclusivity, but that period has also expired.
The product is not protected today by the original patent’s term.
Any current FDA delay would need to arise from a later listed patent, regulatory exclusivity, petition, product-quality issue, or approval-specific requirement.

What is the Orange Book status of US 5,677,331?

US 5,677,331 is an expired patent and cannot presently provide an enforceable exclusionary term. Its historical relationship to Coartem is commercially important, but its current blocking value is zero unless a separate legal issue affects the patent’s status or enforceability.

For an ANDA applicant, the relevant Orange Book analysis is product-specific:

Identify patents listed for the Coartem reference product.
Confirm whether any listed patent remains unexpired.
Determine whether the patent claims the active ingredient, formulation, method of use, or drug substance.
Assess whether a Paragraph IV certification is required.
Review any pediatric exclusivity attached to an unexpired listed patent.

A Paragraph IV certification against US 5,677,331 would have been relevant before expiration. It is no longer a meaningful present-day strategy against this patent because an expired patent cannot support a future 30-month stay or a new exclusionary period.

Which companies challenged or could challenge the patent?

Publicly significant US challenges to the original patent are less important today than later generic competition. The patent expired before the modern US generic market for artemether/lumefantrine matured.

Potential entrants historically would have included:

Generic pharmaceutical companies filing ANDAs for artemether/lumefantrine tablets;
Manufacturers seeking approval of 20 mg/120 mg or equivalent strengths;
Companies developing pediatric dispersible or alternative oral formulations;
Contract manufacturers supplying products for malaria programs.

The main regulatory strategy for a generic product would be an ANDA referencing Coartem, with patent certifications directed at any unexpired Orange Book listings rather than at US 5,677,331.

What formulation patents are separate from US 5,677,331?

US 5,677,331 is not a detailed formulation patent. It does not claim:

A specific excipient system;
A particular tablet-coating composition;
A defined particle-size distribution;
A solid-dispersion or amorphous form;
A particular dissolution specification;
A taste-masked pediatric formulation;
A manufacturing sequence;
A specific polymorph or salt;
A controlled-release delivery system.

Later patent families could create narrower protection around these subjects. A complete freedom-to-operate review must separate the expired foundational combination patent from later rights directed to:

Improved bioavailability;
Stabilized artemether or lumefantrine formulations;
Dispersible tablets;
Pediatric administration;
Manufacturing processes;
Solid-state forms;
Packaging and stability;
Combination dosing regimens.

Such later rights may affect commercial launch even though the original combination patent has expired.

What manufacturing and intellectual-property barriers remain?

The largest post-expiration barriers are technical and regulatory rather than claims-based.

Manufacturing barriers

Artemether/lumefantrine products require control of:

Content uniformity at a low artemether dose;
Lumefantrine solubility and dissolution;
Stability of artemether;
Particle-size and blending behavior;
Bioequivalence under fed conditions;
Tablet disintegration and dissolution;
Moisture and packaging controls;
Reliable supply of both active ingredients.

Lumefantrine has low aqueous solubility, and administration with food affects exposure. A generic product must therefore demonstrate suitable performance under FDA bioequivalence requirements, including fed-state considerations.

Intellectual-property barriers

Potential later rights may cover:

Formulation improvements;
Use in children;
Dispersible dosage forms;
Specific dose schedules;
Manufacturing methods;
Commercial packaging;
Combination products containing additional antimalarial agents.

Those rights must be assessed by patent family and jurisdiction. Expiration of US 5,677,331 does not establish freedom to operate against every later patent connected with Coartem.

How strong is the patent estate for artemether/lumefantrine?

The foundational estate was strong while US 5,677,331 remained unexpired because it directly covered the fixed combination used in the commercial product. Its claim set had three commercial advantages:

It covered both the composition and treatment method.
It captured the 6:1 commercial ratio through claim 4.
It did not depend on a narrow excipient or manufacturing limitation.

Its present strength is limited because the patent has expired. The surviving competitive advantage is more likely to arise from manufacturing scale, FDA-compliant supply, clinical familiarity, procurement relationships, and later formulation rights.

What generic launch scenarios exist?

Scenario 1: Conventional generic tablet

A manufacturer develops a tablet with the same active ingredients and equivalent strengths. Because US 5,677,331 has expired, the primary risks are FDA bioequivalence, current Orange Book patents, and commercial supply economics.

Scenario 2: Pediatric dispersible formulation

A dispersible or child-friendly product may avoid literal overlap with some later formulation claims but remains exposed to any broad composition or method claims that are still unexpired. US 5,677,331 itself would not block launch after expiration.

Scenario 3: Alternative ratio

A product outside the 1:1 to 10:1 ratio could avoid claims 2 through 4. It could still implicate claim 1 or claim 5 if it contains a synergistic oral combination of the two active ingredients. Because the patent is expired, this distinction is now primarily historical.

Scenario 4: Combination with a third active ingredient

A triple-active product may have a non-infringement argument under the "consists of" language in claim 1. It would face separate regulatory, clinical, labeling, and patent issues.

How does US 5,677,331 compare with later patent protection?

Issue	US 5,677,331	Later formulation or process patents
Active ingredients	Lumefantrine and artemether	May claim improved forms or delivery systems
Dosage form	Broad oral composition	Often narrow and technically specific
Ratio	1:1 to 10:1, with narrower dependent ranges	May specify exact strengths or release profiles
Treatment method	Oral malaria treatment	May target populations, dosing schedules, or indications
Manufacturing	Not the principal focus	May claim processes, particle engineering, or stability
Current status	Expired	Must be reviewed individually
Generic risk	No current blocking effect	Depends on patent term, listing, and claim scope

Key Takeaways

US Patent 5,677,331 covers the oral fixed combination of lumefantrine, formerly benflumetol, and artemether.
Claims 1 through 4 cover pharmaceutical compositions; claim 5 covers oral treatment of malaria.
The central commercial ratio is 6:1 lumefantrine to artemether, reflected in claim 4 and in the Coartem tablet strength.
The patent issued on October 14, 1997, and expired around 2015 under the ordinary US patent term.
The patent is no longer a current US barrier to generic artemether/lumefantrine entry.
Biosimilar analysis does not apply because Coartem is a small-molecule drug.
Current launch risk depends on later patents, Orange Book listings, FDA requirements, manufacturing capability, and commercial supply economics.
The patent’s strongest historical feature was its direct coverage of both the fixed combination and the malaria treatment method.

FAQs

Is benflumetol the same as lumefantrine?

Yes. Benflumetol is the earlier name used in US Patent 5,677,331 for lumefantrine, the quinoline-based antimalarial used with artemether in Coartem.

Does US 5,677,331 cover Coartem tablets specifically?

It covers the active combination in an oral pharmaceutical composition and reaches the commercial 6:1 ratio through claim 4. It does not require the Coartem trademark, a specific tablet shape, or a particular excipient system.

Can a generic use a different lumefantrine-to-artemether ratio?

A different ratio could avoid dependent claims 2 through 4 if it falls outside their ranges. Historically, claim 1 and claim 5 could still have presented broader combination-related issues. The patent’s expiration eliminates that current US patent barrier.

Does the patent cover artemether or lumefantrine alone?

No. The patent claims the combination. It does not independently claim either active ingredient as a standalone antimalarial.

Does a new pediatric formulation require a patent license from the original patent owner?

Not because of US 5,677,331 after its expiration. A license could still be relevant for an unexpired later patent, trademark, technology-transfer agreement, or proprietary manufacturing technology.

References

U.S. Food and Drug Administration. (2009, April 8). FDA approves Coartem for treatment of uncomplicated malaria. https://www.fda.gov
United States Patent and Trademark Office. (1997). U.S. Patent No. 5,677,331: Antimalarial pharmaceutical compositions containing artemether and benflumetol.
Novartis Pharmaceuticals Corporation. (2009). Coartem prescribing information. U.S. Food and Drug Administration.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
China	90106722.9	Aug 08, 1990
China	91102575.8	Apr 24, 1991

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0500823	⤷ Start Trial	SPC/GB00/013	United Kingdom	⤷ Start Trial
European Patent Office	0500823	⤷ Start Trial	C300048	Netherlands	⤷ Start Trial
European Patent Office	0500823	⤷ Start Trial	2001C/043	Belgium	⤷ Start Trial
African Regional IP Organization (ARIPO)	231	⤷ Start Trial
African Regional IP Organization (ARIPO)	9100275	⤷ Start Trial
Austria	135209	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,677,331

Summary for Patent: 5,677,331