List of Excipients in Branded Drug METHIMAZOLE

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Generic Drugs Containing METHIMAZOLE

Company	Ingredient	NDC	Excipient
Eon Labs Inc	methimazole	0185-0205	ANHYDROUS LACTOSE
Eon Labs Inc	methimazole	0185-0205	LACTOSE MONOHYDRATE
Eon Labs Inc	methimazole	0185-0205	MAGNESIUM STEARATE

What are the Most Frequently-Used Excipients in METHIMAZOLE?

# Of NDCs	Excipient
3	ANHYDROUS LACTOSE
67	LACTOSE MONOHYDRATE
67	MAGNESIUM STEARATE

Last updated: August 14, 2026

Methimazole is a mature, low-cost generic with limited conventional patent protection. The strongest commercial opportunities are formulation-led: pediatric and geriatric oral liquids, dose-flexible tablets, veterinary products, taste-masked presentations, and differentiated packaging. Excipient selection should prioritize chemical stability, rapid dissolution, dose uniformity, palatability, and low-cost manufacturing rather than creating a complex delivery system.

Methimazole Excipient Strategy, Patent Landscape, and Commercial Opportunities

What is the commercial position of methimazole?

Methimazole is an oral thioamide used to treat hyperthyroidism and Graves' disease. In the United States, it is marketed primarily as generic immediate-release tablets in 5 mg and 10 mg strengths. The drug has no meaningful remaining composition-of-matter exclusivity, and standard tablet products compete largely on price, supply reliability, wholesaler access, and regulatory execution.

Methimazole also has an important veterinary market. Felimazole, an enteric-coated methimazole tablet marketed by Elanco for cats, demonstrates that formulation and species-specific administration can support branded commercial positioning even when the active ingredient is old and widely available.[1]

A separate human oral solution, Thyquidity, provides a regulatory and commercial precedent for liquid methimazole. The product is a 5 mg/mL oral solution intended to improve dose administration when tablets are unsuitable.[2]

Attribute	Methimazole market position
Active ingredient	Methimazole
Primary human uses	Hyperthyroidism and Graves' disease
Common human dosage forms	Immediate-release tablets; oral solution
Common tablet strengths	5 mg and 10 mg
Human market structure	Generic-dominated
Veterinary product	Felimazole coated tablets
Principal opportunity	Formulation, dosing flexibility, palatability, supply
Core patent risk	Low for the active ingredient; product-specific claims may remain relevant

What patents protect methimazole products?

The original active-ingredient patent estate is expired. Current commercial protection is more likely to arise from formulation patents, method-of-use claims, trademarks, regulatory exclusivity, manufacturing know-how, and product-specific intellectual property.

For standard methimazole tablets, the competitive barrier is low. Generic manufacturers generally rely on abbreviated new drug applications and demonstrate pharmaceutical equivalence and bioequivalence to the relevant reference product. FDA Orange Book patent listings, where present, must be evaluated product by product because patents attach to specific approved products and not to the active ingredient in the abstract.[3]

What is the Orange Book status of methimazole?

Generic methimazole tablets do not generally have a material Orange Book patent barrier. An oral-solution NDA may have product-specific regulatory records that differ from generic tablet listings. The Orange Book should be reviewed by NDA number, dosage form, and strength before filing or acquisition decisions.[3]

The practical conclusion is that a new tablet applicant is unlikely to face a conventional Paragraph IV campaign against an active methimazole patent. The more relevant questions are:

• Whether the proposed dosage form is therapeutically equivalent to a listed reference product.
• Whether a liquid product requires a 505(b)(2) strategy.
• Whether the formulation uses a protected taste-masking, coating, or delivery technology.
• Whether method-of-use claims affect a narrower patient population.
• Whether a veterinary product has separate formulation or use claims.

When does methimazole lose exclusivity?

Methimazole's active-ingredient exclusivity expired long ago. Standard tablet products are therefore commercially exposed to generic competition and do not depend on new chemical entity exclusivity.

For a newly developed methimazole formulation, exclusivity depends on the regulatory pathway:

Development route	Potential protection	Commercial implication
ANDA for an equivalent tablet	Generally no independent clinical exclusivity	Lowest development cost and lowest market protection
505(b)(2) oral solution	Possible product-specific regulatory exclusivity, depending on approval basis	Supports differentiation if the product solves administration or dosing problems
New pediatric formulation	Potential pediatric and formulation-related regulatory benefits	Requires clinical and regulatory justification
Veterinary NDA	Product-specific approval and possible patent or exclusivity rights	Can support premium pricing and species-specific positioning
OTC or nonprescription route	Requires a separate regulatory basis	Not an established primary pathway for methimazole

The commercial value of a new methimazole product depends more on the size and defensibility of its formulation advantage than on the underlying molecule.

What excipients are used in methimazole tablets?

Commercial methimazole tablets use conventional excipients found in immediate-release solid oral dosage forms. Depending on the manufacturer, these can include fillers, binders, disintegrants, lubricants, and coloring agents. Public product labeling should be used as the controlling source for each marketed product because inactive ingredients vary by manufacturer.[4]

A practical excipient platform may include:

Excipient function	Candidate classes	Development rationale
Diluent	Lactose, microcrystalline cellulose, dibasic calcium phosphate	Controls tablet weight and supports content uniformity
Binder	Povidone, pregelatinized starch, hydroxypropyl cellulose	Improves granule and tablet strength
Disintegrant	Croscarmellose sodium, crospovidone, sodium starch glycolate	Supports rapid release at low drug load
Lubricant	Magnesium stearate, sodium stearyl fumarate	Supports compression and ejection
Glidant	Colloidal silicon dioxide	Improves powder flow
Film former	Hypromellose-based coating systems	Supports identification, swallowability, and appearance
Colorant	Approved lake pigments or iron oxides	Supports strength differentiation and product recognition

Methimazole tablets contain a relatively low drug load at the 5 mg and 10 mg strengths. Excipient selection therefore has a direct effect on dose uniformity. A formulation that relies on low-dose blending must control segregation, particle-size distribution, mixing time, and hopper behavior.

What formulation properties matter most?

The target profile for a conventional tablet should include:

• Rapid and consistent disintegration.
• Immediate-release dissolution across relevant pH conditions.
• Uniform content at both 5 mg and 10 mg strengths.
• Low friability and adequate mechanical strength.
• Stability under heat and humidity.
• Low tablet weight suitable for pediatric and geriatric administration.
• A coating or imprint system that clearly distinguishes strengths.

Direct compression can minimize process steps, but wet granulation may improve blend uniformity when particle-size or flow properties are unfavorable. The preferred process should be established through comparative development work rather than selected solely for cost.

How should excipients be selected for methimazole stability?

Methimazole formulation development should assess moisture, light, pH, oxidation, and interaction with reactive excipients. Stability studies should include the active ingredient, degradation products, dissolution, assay, content uniformity, and physical attributes.

Moisture control

Moisture-sensitive excipient combinations can affect tablet hardness, disintegration, and chemical stability. Packaging options include high-barrier blisters, induction-sealed bottles, and desiccant-containing containers. A moisture-barrier package may provide greater value than adding a complex excipient system.

pH and liquid formulations

An oral solution creates a different development problem from a tablet. The formulation must control pH, preservative performance, microbial quality, flavor, and chemical stability. Candidate systems may include purified water, a buffering agent, a sweetener, a flavor system, a viscosity modifier, and a preservative.

The formulation should avoid unnecessary excipients that increase pediatric exposure or complicate regulatory review. The preservative system should be validated through antimicrobial effectiveness testing, and the product should be assessed after in-use storage and repeated opening.

Oxidation and sulfur chemistry

Methimazole contains sulfur, so oxidative degradation should be assessed during preformulation and packaging studies. The development program should evaluate oxygen exposure, peroxide-containing excipients, headspace, light, and container closure performance. Excipient lots should be screened for peroxide or other reactive impurities when relevant to the formulation.

What formulations are protected by methimazole patents?

Potentially protectable formulation categories include:

1. Stable methimazole oral solutions.
2. Taste-masked liquids and multiparticulates.
3. Enteric-coated veterinary tablets.
4. Modified-release dosage forms.
5. Orally disintegrating tablets.
6. Sprinkle formulations for patients unable to swallow tablets.
7. Unit-dose liquid presentations.
8. Novel combinations of excipients that improve stability or palatability.

Patent strength depends on whether the claims cover a reproducible technical effect. A broad claim to "methimazole with conventional excipients" is vulnerable. A stronger position would require a defined composition, concentration range, manufacturing condition, or performance result that is difficult to design around.

How strong is the patent estate for methimazole?

The estate is weak for the molecule and conventional tablets, but it can be moderate for a technically differentiated product. The strongest potential claims would generally involve:

• Narrow pH and preservative ranges linked to stability.
• Specific taste-masking systems with demonstrated sensory performance.
• Defined coating layers and dissolution profiles.
• A pediatric dosing system with measurable administration benefits.
• A manufacturing process that produces a distinctive impurity or particle-size profile.
• A veterinary dosage form with a validated species-specific pharmacokinetic or tolerability advantage.

A formulation patent should be filed before public disclosure, pilot commercialization, or publication of stability data. Freedom-to-operate analysis should cover both composition claims and process claims.

What commercial opportunities exist for methimazole excipients?

Pediatric and geriatric oral liquids

An oral liquid is the clearest human formulation opportunity. Patients may require doses that do not align with 5 mg or 10 mg tablets, and children may have difficulty swallowing tablets. A 5 mg/mL solution allows measured doses using an oral syringe.

Commercial differentiation can come from:

• A calibrated oral syringe.
• Low-volume dosing.
• Improved taste masking.
• Child-resistant packaging with senior-friendly usability.
• Unit-dose cups or premeasured syringes.
• A stable shelf life after opening.
• Reduced need for pharmacy compounding.

The product must compete with pharmacy-compounded methimazole liquids, which may be less expensive but have variable availability, stability, and flavor performance.

Orally disintegrating or dispersible tablets

An orally disintegrating tablet could address swallowing difficulty without the microbial and preservative burdens of a liquid. The low dose is compatible with a small tablet, but taste is a central issue because rapid oral disintegration increases exposure to the tongue.

Useful excipient technologies include mannitol-based matrices, crospovidone, low-substituted hydroxypropyl cellulose, and flavor or sweetener systems. Direct compression may support low-cost production, while porous granules or lyophilized structures could improve disintegration at higher cost.

Sprinkle capsules and multiparticulates

A sprinkle product could allow administration with soft food. Multiparticulates may also support taste masking through polymer coating. The main development risks are dose recovery, content uniformity after sprinkling, coating integrity, and food-effect performance.

This format could be commercially relevant for pediatric patients and adults with swallowing limitations, but the product must demonstrate that the intended administration method does not alter dose delivery or stability.

Veterinary products

The veterinary segment supports premium positioning where the product improves administration or tolerability. Felimazole uses coated tablets, showing that veterinary methimazole products can be differentiated from human generics through species-specific labeling, tablet design, and veterinary distribution.[1]

Potential opportunities include:

• Smaller-dose tablets for cats.
• Flavored oral liquids.
• Transdermal formulations, subject to efficacy and regulatory requirements.
• Easier-to-administer unit-dose packaging.
• Products designed for long-term treatment and dose titration.

Transdermal methimazole has been used in veterinary practice, but absorption can be variable. A commercial product would require rigorous evidence of systemic exposure, dose consistency, and clinical effectiveness.

Which companies are challenging methimazole products?

The human market is mainly supplied by generic manufacturers, while the veterinary branded segment includes Elanco's Felimazole. Commercial competition is likely to come from generic tablet suppliers, specialty pharmacies producing compounded liquids, and companies developing differentiated oral solutions rather than from large-scale innovation in the active ingredient.

A new entrant should expect competition on:

• Wholesale acquisition price.
• Backorder performance.
• National wholesaler coverage.
• Pharmacy substitution status.
• Hospital and endocrinology formulary access.
• Veterinary clinic distribution.
• Liquid availability and flavor quality.

What generic entry risks exist for methimazole?

Generic entry risk is high for conventional tablets because the active ingredient is mature, manufacturing processes are established, and clinical differentiation is limited. A new tablet product would face price compression unless it offers a supply, packaging, or channel advantage.

Risk is lower for a differentiated liquid or pediatric product if the product has:

• A distinct regulatory pathway.
• A reliable stability profile.
• A clinically useful dosing concentration.
• Strong taste acceptance.
• Patent claims covering the formulation.
• Distribution relationships that reduce pharmacy compounding substitution.

Paragraph IV litigation is more likely to arise against a listed formulation patent than against the methimazole molecule. The absence of a major active-ingredient patent does not eliminate the need to review Orange Book listings, published patent applications, veterinary patents, and formulation claims in relevant jurisdictions.

How does methimazole compare with competing hyperthyroidism products?

Product	Active ingredient	Main dosage form	Formulation opportunity
Methimazole	Methimazole	Tablets and oral solution	Pediatric liquid, ODT, sprinkle, veterinary products
Propylthiouracil	Propylthiouracil	Tablets	Alternative thioamide; different safety and dosing profile
Radioactive iodine	Iodine-131	Nuclear medicine	Definitive treatment rather than chronic oral dosing
Carbimazole	Prodrug of methimazole	Tablets in some markets	Geographic and regulatory alternative
Veterinary methimazole	Methimazole	Coated tablets, compounded products	Taste, dose titration, administration compliance

Methimazole remains attractive for formulation development because it is used chronically, has multiple dose levels, and creates practical administration problems for pediatric, geriatric, and veterinary patients.

What FDA regulatory pathway applies to a new methimazole product?

A conventional tablet matching an approved reference product would generally be developed through an ANDA. A novel oral solution, orally disintegrating tablet, or other dosage form may require a 505(b)(2) application if the applicant relies partly on FDA findings for an approved product but introduces a clinically meaningful formulation change.[5]

The regulatory package should address:

• Pharmaceutical equivalence.
• Bioequivalence or comparative exposure.
• Dissolution and release performance.
• Excipient safety at the proposed dose.
• Stability and container closure.
• Preservative effectiveness for liquids.
• Human factors for dosing devices.
• Pediatric administration, where applicable.
• In-use stability and dose withdrawal accuracy.

What licensing deals could support methimazole commercialization?

Methimazole is more likely to support targeted commercial agreements than large discovery-stage licensing transactions. Relevant deal structures include:

• Acquisition or licensing of a stable oral-solution formulation.
• Contract manufacturing of low-dose tablets.
• Exclusive distribution for veterinary products.
• Licensing of taste-masking or coating technology.
• Co-development of a pediatric dosage form.
• Supply agreements with specialty pharmacies or hospital systems.

The most valuable partner assets are likely to be regulatory-ready formulation data, commercial-scale manufacturing capability, and distribution access rather than ownership of the active ingredient.

Key Takeaways

• Methimazole is a mature, generic-dominated drug with limited active-ingredient patent protection.
• Conventional 5 mg and 10 mg tablets offer low patent defensibility and high price competition.
• Oral solutions, orally disintegrating tablets, sprinkle products, and veterinary formulations provide the strongest excipient-led opportunities.
• Liquid products require careful control of pH, preservatives, taste, microbial quality, and in-use stability.
• Low-dose tablets require strong control of blend uniformity, segregation, and content uniformity.
• A defensible patent position would need to cover a defined formulation and demonstrated technical performance.
• FDA pathway selection is central: an equivalent tablet may fit an ANDA, while a differentiated dosage form may require a 505(b)(2) application.
• The most attractive commercial strategy is a formulation that reduces pharmacy compounding, improves dosing accuracy, or increases treatment compliance.

FAQs

Can methimazole be formulated as a pediatric oral suspension?

Yes. A suspension can provide dose flexibility, but it requires control of sedimentation, redispersibility, dose uniformity, microbial quality, and flavor. A clear oral solution may offer simpler dose withdrawal if chemical solubility and stability are adequate.

Is methimazole suitable for an orally disintegrating tablet?

Yes. The low dose is technically compatible with an orally disintegrating tablet. Taste masking is the main development challenge because the drug contacts the oral cavity during disintegration.

Can a methimazole formulation receive new patent protection?

Yes, but protection would need to arise from a novel formulation, process, coating, delivery system, or demonstrated technical effect. Conventional combinations of common tablet excipients are unlikely to provide broad, durable protection.

Are compounded methimazole liquids a major commercial competitor?

Yes. Compounded liquids can compete with commercial oral solutions, particularly where pharmacies can prepare patient-specific concentrations. A commercial product can differentiate through validated stability, standardized concentration, dosing devices, consistent flavor, and wider distribution.

What is the most attractive methimazole product concept?

A stable, palatable, dose-flexible oral liquid with an integrated oral syringe is the strongest human formulation concept. In veterinary medicine, small-dose, palatable, easy-to-administer products have the clearest premium opportunity.

References

1. Elanco Animal Health. (2023). Felimazole coated tablets prescribing information. U.S. Food and Drug Administration, Center for Veterinary Medicine.

2. Tris Pharma, Inc. (2020). Thyquidity (methimazole) oral solution prescribing information. U.S. Food and Drug Administration.

3. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/

4. U.S. National Library of Medicine. (2024). DailyMed: Methimazole tablet labeling. https://dailymed.nlm.nih.gov/

5. U.S. Food and Drug Administration. (2024). Applications covered by section 505(b)(2). https://www.fda.gov/drugs/development-resources/applications-covered-section-505b2