United States Patent 4,562,060: Scope, Claims, Expiration, and Lidocaine-Prilocaine Patent Landscape

U.S. Patent No. 4,562,060 covers a topical local-anesthetic product and method using a homogeneous oil formed from prilocaine base and lidocaine base. The claimed weight ratio is 42:58 to 80:20 prilocaine-to-lidocaine, and the mixture must have a melting point below 40°C. Based on the claims provided, the patent is narrow because it requires both the specific base combination and a paper carrier.

The patent issued on December 31, 1985, and its original U.S. term expired on December 31, 2002, under the pre-Uruguay Round patent-term rule of 17 years from issuance. The patent therefore does not create a current U.S. barrier to generic lidocaine-prilocaine products. Any later patent risk would have to arise from separate formulation, delivery-device, manufacturing, or method-of-use patents.

What does U.S. Patent 4,562,060 cover?

The patent covers two related subject matters:

A locally active anesthetic article consisting of paper embedded with a homogeneous oil.
A method of obtaining topical local anesthesia by administering that paper article to a mammal.

The oil is made from:

Prilocaine in its free-base form;
Lidocaine in its free-base form;
A prilocaine-to-lidocaine weight ratio of 42:58 to 80:20; and
A resulting melting point below 40°C.

The claimed technology is associated with the eutectic lidocaine-prilocaine system later commercialized in topical anesthetic products such as EMLA. The eutectic mixture remains liquid or semi-liquid at temperatures suitable for topical application, allowing the two solid anesthetic bases to be used as a homogeneous oil rather than as separate crystalline solids.

Patent identification

Item	Data
U.S. patent	4,562,060
Issue date	December 31, 1985
Technology	Topical lidocaine-prilocaine anesthetic mixture
Active ingredients	Prilocaine base and lidocaine base
Claimed ratio	42:58 to 80:20, prilocaine-to-lidocaine by weight
Physical limitation	Homogeneous oil with melting point below 40°C
Delivery form in supplied claims	Paper embedded with the oil
Claim types	Product/article and method of treatment
Original term	17 years from issue
Expiration	December 31, 2002
Current status	Expired

The patent’s commercial relevance is primarily historical. The claimed eutectic concept became the technical basis for topical lidocaine-prilocaine anesthesia, but the patent itself no longer provides enforceable U.S. exclusivity.

How should claim 1 be construed?

Claim 1 requires an anesthetic article comprising paper embedded with the specified oil. Each limitation matters.

Required chemical form

The claim requires both anesthetics in the form of their bases. Lidocaine hydrochloride and prilocaine hydrochloride, used as salts, would not literally satisfy the base-form limitation.

This distinction is important because topical products can contain active ingredients as free bases, salts, or combinations of both. A product using lidocaine hydrochloride or prilocaine hydrochloride instead of the claimed free bases would require a separate infringement analysis, including possible doctrine-of-equivalents issues. The literal claim language favors the free-base forms.

Required ratio

The claimed ratio is:

Component	Lower bound	Upper bound
Prilocaine base	42 parts	80 parts
Lidocaine base	58 parts	20 parts

The range is expressed as a weight ratio of prilocaine to lidocaine. The endpoints appear included because the claim uses the range "42:58 to 80:20" without an exclusion.

A formulation containing 42% prilocaine and 58% lidocaine would fall at one stated boundary. A formulation containing 80% prilocaine and 20% lidocaine would fall at the other. A formulation outside the range would not literally meet this limitation.

The commonly known EMLA composition uses approximately equal concentrations of lidocaine and prilocaine, often described as 2.5% lidocaine and 2.5% prilocaine in the finished cream. That ratio is within the patent’s claimed range.

Homogeneous-oil requirement

The active ingredients must form a homogeneous oil. The claim is not directed merely to any physical mixture of lidocaine and prilocaine. It requires a single oil phase or homogeneous oily mixture with the stated melting behavior.

A formulation in which the anesthetics remain separate crystals, form a suspension, or are dissolved in a separate solvent system may raise questions about whether the claimed "homogeneous oil" limitation is satisfied.

Melting-point requirement

The resulting mixture must have a melting point below 40°C. This limitation ties the claim to a low-melting eutectic or near-eutectic composition.

The limitation is technically significant because it distinguishes the claimed mixture from compositions that remain solid at ordinary handling or skin temperature. Testing methodology would matter in an enforcement dispute. A party would likely examine:

The ratio of free-base lidocaine and prilocaine;
Whether the mixture is homogeneous;
The measured melting or softening range;
Water content and excipients;
Whether the tested material is the active mixture or the finished product.

Paper limitation

Based on the claim language supplied, the product must comprise paper embedded with the anesthetic oil. This is a meaningful structural limitation. A cream, gel, ointment, film, foam, solution, or non-paper patch would not necessarily satisfy the literal paper limitation.

The phrase "comprising" makes the claim open-ended as to additional components. A product can contain additional excipients or backing materials and still potentially fall within the claim. The phrase "consisting essentially of" narrows the active oil composition by excluding ingredients that materially alter the basic and novel characteristics of the lidocaine-prilocaine oil.

How should claim 2 be construed?

Claim 2 is a method claim directed to topical anesthesia in mammals. It requires:

A patient or mammal;
Topical administration;
An anesthetically effective amount;
Prilocaine base and lidocaine base;
The claimed 42:58 to 80:20 weight ratio;
A homogeneous oil;
A melting point below 40°C; and
Administration using the claimed paper article.

The method claim is narrower than a general method of administering lidocaine and prilocaine. It does not cover every topical use of the two anesthetics. The method requires the specified composition and paper delivery format.

The "anesthetically effective amount" is functional language. It generally requires that the administered amount produce local anesthesia under the claimed use. A paper article containing the mixture but used for a non-anesthetic purpose would present a different infringement question.

What is the patent’s legal status and expiration date?

U.S. Patent 4,562,060 is expired. It issued in 1985, when U.S. utility patents generally received a term of 17 years from issuance. The resulting expiration date was December 31, 2002. The patent cannot currently block manufacture, sale, or use in the United States based on its original claims.

Event	Date
U.S. patent issued	December 31, 1985
17-year patent term begins from issue under historical law	December 31, 1985
Patent expiration	December 31, 2002
Current enforceability	None based on the expired patent

Foreign priority filings do not ordinarily extend the term of a pre-1995 U.S. patent under the applicable historical term rules. Patent-term adjustment and patent-term extension regimes also postdate the relevant issuance framework and would not ordinarily revive an expired patent.

What FDA regulatory status is associated with the lidocaine-prilocaine product?

The principal U.S. reference product associated with topical lidocaine-prilocaine anesthesia is EMLA cream, containing lidocaine and prilocaine. EMLA was approved through the new drug application pathway rather than the biologics license application pathway.

The product is a small-molecule topical anesthetic. Consequently:

Biosimilar approval is not the relevant pathway.
Generic competition proceeds primarily through abbreviated new drug applications.
The relevant regulatory issues include pharmaceutical equivalence, bioequivalence or other applicable equivalence standards, labeling, strength, dosage form, and inactive ingredients.
Patent certification issues under Paragraph IV can apply to listed patents, but the focal patent expired before the modern generic market developed.

Orange Book implications

The Orange Book identifies patents and exclusivity associated with approved drug products. An expired patent cannot support a current Orange Book-based stay or block generic approval.

For a lidocaine-prilocaine product, the practical analysis should separate:

Historical listing of patents associated with the reference product;
Current listing status;
Expiration or delisting;
Any later patents covering a specific formulation, device, or use; and
Whether the FDA considers the later patent to claim the approved drug product or an approved method of use.

U.S. Patent 4,562,060 is not a current patent barrier because its term ended in 2002. A Paragraph IV challenge directed solely to this patent would have no current economic value.

Were there Paragraph IV challenges to U.S. Patent 4,562,060?

The patent’s expiration predates the principal generic competition period for lidocaine-prilocaine cream. A Paragraph IV certification would have been relevant only while the patent remained listed and unexpired.

The statutory framework permits an ANDA applicant to certify that a listed patent is invalid, unenforceable, or will not be infringed. A notice of Paragraph IV certification can trigger patent litigation and, in qualifying circumstances, a 30-month stay of approval under the Hatch-Waxman Act. Those mechanisms do not revive an expired patent. Once the patent expired on December 31, 2002, the patent could no longer support a prospective 30-month stay.

The available commercial record is more consistent with post-expiration generic entry than with a continuing litigation dispute over this patent. Current generic products therefore face no enforceable exclusion based on U.S. Patent 4,562,060.

What patents protect lidocaine-prilocaine creams and delivery systems?

The patent landscape is broader than the focal patent. Relevant patent categories include the following.

Eutectic active-mixture patents

These patents claim the combination of lidocaine and prilocaine bases, often with a low melting point or eutectic behavior. U.S. Patent 4,562,060 is the central historical example.

Because the patent has expired, the core free-base eutectic concept is generally available for commercial use in the United States, subject to any later patent claims that add formulation or device limitations.

Formulation patents

Later patents can claim:

Specific oil-in-water emulsions;
Particle-size distributions;
Preservative systems;
Thickening agents;
pH ranges;
Water activity;
Improved stability;
Reduced irritation;
Enhanced skin penetration; or
Specific concentration profiles.

A generic product can practice the expired active-mixture concept while avoiding a later formulation patent by changing excipients, manufacturing conditions, or physical characteristics.

Delivery-device patents

A separate patent may cover:

Adhesive patches;
Occlusive dressings;
Drug-loaded films;
Laminated papers;
Microneedle systems;
Applicators;
Premeasured dosage units; or
Combination packages containing the anesthetic and a delivery article.

The paper limitation in the supplied claims makes delivery format particularly important. A later patch or film patent could create a separate freedom-to-operate issue even though the original eutectic patent has expired.

Method-of-use patents

Method claims may cover use before:

Venipuncture;
Needle insertion;
Minor dermatological procedures;
Pediatric procedures;
Laser procedures;
Vaccination; or
Specific treatment of intact or damaged skin.

A later method-of-use patent would need to claim a legally distinct use from the broad topical-anesthesia method in claim 2. It could still be relevant if the approved labeling or commercial instructions encourage the patented use.

How strong is the patent estate for this technology?

The focal patent estate is commercially weak today because the only identified patent is expired. Its original scope was also narrower than a general lidocaine-prilocaine composition patent because of the paper-carrier, homogeneous-oil, ratio, and melting-point requirements.

Strength factor	Assessment
Core active combination	Historically important, now expired
Free-base requirement	Narrows literal scope
Ratio limitation	Narrows products outside 42:58 to 80:20
Melting-point limitation	Requires technical proof
Homogeneous-oil limitation	Creates formulation-specific scope
Paper-carrier limitation	Excludes many creams and non-paper products
Method claim	Limited by the same composition and carrier requirements
Current blocking power	None from Patent 4,562,060
Biosimilar relevance	None; this is a small-molecule product
Generic risk	Low from the expired patent; potentially separate risk from later patents

The patent’s historical strength came from claiming the eutectic mixture in a form suitable for topical delivery. Its current weakness is term expiration, not necessarily technical invalidity.

What generic launch scenarios exist?

Cream or ointment launch

A generic lidocaine-prilocaine cream can generally rely on the expired status of U.S. Patent 4,562,060. The principal regulatory work concerns pharmaceutical equivalence, bioequivalence or comparative performance, labeling, manufacturing controls, and inactive ingredients.

Paper or film product launch

A paper-based product may practice the expired claim concept directly. A sponsor would still need to review later patents covering the paper structure, adhesive, occlusion, packaging, dosage control, or manufacturing process.

Non-eutectic formulation

A product using separate salts, a different anesthetic ratio, or a non-homogeneous formulation may avoid literal infringement of the focal claims. Such changes could also affect product performance and FDA equivalence requirements.

Improved formulation launch

An improved cream may avoid later patents through a different excipient system while retaining lidocaine and prilocaine as active ingredients. The expired patent does not prevent this strategy.

What geographic coverage does the patent provide?

U.S. Patent 4,562,060 provided protection only in the United States. Foreign counterparts, if granted, required separate term and legal-status analysis in each jurisdiction.

The commercial concept was subject to international patent protection through related foreign filings, but expiration dates could differ because of:

Different filing dates;
National-phase timing;
Local patent-term rules;
Supplementary protection certificates;
Patent-term extensions; and
National revocation or lapse events.

A U.S. freedom-to-operate conclusion cannot be extended automatically to Europe, Canada, Japan, China, or other markets.

What manufacturing and intellectual-property barriers remain?

The expired patent removes the principal composition barrier, but practical barriers remain:

Reproducible formation of the lidocaine-prilocaine eutectic;
Control of water content and phase behavior;
Uniform drug loading;
Stability of the emulsion or oil phase;
Skin penetration performance;
Control of local irritation;
Packaging compatibility;
Microbiological quality;
Manufacturing process validation; and
Regulatory demonstration of equivalence.

Manufacturing know-how, trade secrets, and later patents may remain valuable even when the foundational patent is expired. These rights do not extend the term of U.S. Patent 4,562,060, but they can affect development cost and launch timing.

How does U.S. Patent 4,562,060 compare with current generic competition?

Issue	EMLA-type reference product	Generic lidocaine-prilocaine product
Active ingredients	Lidocaine and prilocaine	Usually the same active ingredients
Historical technical basis	Eutectic free-base mixture	May use the same or a technically equivalent system
Original focal patent	U.S. 4,562,060	Expired and not blocking
FDA pathway	NDA	ANDA or other applicable abbreviated pathway
Biosimilar pathway	Not applicable	Not applicable
Current patent risk from 4,562,060	None	None
Main competitive factors	Brand recognition, supply, labeling	Price, approval, manufacturing, distribution
Potential remaining IP	Formulation, device, use, process	Same categories

Key Takeaways

U.S. Patent 4,562,060 claims a lidocaine-prilocaine free-base mixture in a 42:58 to 80:20 ratio.
The mixture must be a homogeneous oil with a melting point below 40°C.
The supplied claims require a paper carrier embedded with the oil.
Claim 1 is an article or product claim; claim 2 is a topical-anesthesia method claim.
The patent issued on December 31, 1985, and expired on December 31, 2002.
The patent no longer blocks U.S. generic lidocaine-prilocaine products.
The patent is not relevant to biosimilar competition because lidocaine and prilocaine are small-molecule drugs.
Current freedom-to-operate analysis should focus on later formulation, delivery-device, manufacturing, and method-of-use patents.
A cream, gel, film, patch, or other non-paper dosage form may avoid the literal paper limitation in the supplied claims.
The core eutectic concept is commercially available in the United States after expiration, subject to separate later rights.

Frequently Asked Questions

Does U.S. Patent 4,562,060 cover EMLA cream?

It is historically associated with the lidocaine-prilocaine eutectic technology used in EMLA-type products. Based strictly on the supplied claim language, the paper-carrier limitation makes the claims narrower than a general claim to every lidocaine-prilocaine cream.

Can a company launch a generic lidocaine-prilocaine product based on expiration of this patent?

Yes. The patent expired on December 31, 2002. A launch still requires compliance with FDA approval requirements and review of later patents covering specific formulations, devices, uses, or manufacturing processes.

Does the 42:58 to 80:20 ratio apply to the finished cream?

The claim expresses the ratio for prilocaine base to lidocaine base in the claimed mixture. It should not automatically be calculated from total cream weight or from the concentration of all ingredients.

Does the patent cover lidocaine and prilocaine hydrochloride salts?

The supplied claims specify prilocaine and lidocaine in the form of their bases. Salt-only formulations would not literally satisfy that limitation.

Is a lidocaine-prilocaine patch still exposed to this patent?

No current U.S. exposure arises from Patent 4,562,060 because it expired. A patch could face separate later patents directed to the patch structure, adhesive, backing, dosage control, or method of use.

References

United States Patent and Trademark Office. (1985). U.S. Patent No. 4,562,060, locally active anesthetic agent. U.S. Department of Commerce.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs. FDA.
United States Congress. (1984). Drug Price Competition and Patent Term Restoration Act of 1984, Pub. L. No. 98-417, 98 Stat. 1585.
United States Code. (1982). 35 U.S.C. § 154: Contents and term of patent; provisional rights. Congress.gov.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Sweden	7713618	Dec 01, 1977

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	218948	⤷ Start Trial
Austria	364451	⤷ Start Trial
Austria	A859578	⤷ Start Trial
Australia	4196078	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 4,562,060