List of Excipients in Branded Drug PROPYLTHIOURACIL

Company	Tradename	Ingredient	NDC	Excipient	Potential Generic Entry
Endo USA Inc	PROPYLTHIOURACIL	propylthiouracil	67253-651	CELLULOSE, MICROCRYSTALLINE
Endo USA Inc	PROPYLTHIOURACIL	propylthiouracil	67253-651	DOCUSATE SODIUM
Endo USA Inc	PROPYLTHIOURACIL	propylthiouracil	67253-651	MAGNESIUM STEARATE

Generic Drugs Containing PROPYLTHIOURACIL

Company	Ingredient	NDC	Excipient
Actavis Pharma Inc	propylthiouracil	0228-2348	LACTOSE MONOHYDRATE
Actavis Pharma Inc	propylthiouracil	0228-2348	MAGNESIUM STEARATE
Actavis Pharma Inc	propylthiouracil	0228-2348	POVIDONE

What are the Most Frequently-Used Excipients in PROPYLTHIOURACIL?

# Of NDCs	Excipient
4	ANHYDROUS LACTOSE
1	CALCIUM STEARATE
5	CELLULOSE, MICROCRYSTALLINE

Propylthiouracil Excipient Strategy and Commercial Opportunities

Last updated: August 3, 2026

Propylthiouracil (PTU) is a low-cost, mature antithyroid drug with limited active-ingredient patent protection and modest commercial scale. The strongest opportunities are not new-molecule exclusivity plays. They are differentiated oral formulations that address hepatotoxicity-related monitoring, pediatric dosing, taste, swallowing difficulty, hospital use, and supply reliability.

The most commercially credible products are:

1. A ready-to-use oral suspension for pediatric patients and adults unable to swallow tablets.
2. A taste-masked suspension or dispersible tablet for children.
3. A low-excipient, rapidly disintegrating tablet for dysphagia and thyroid-storm settings.
4. A stable unit-dose hospital formulation that reduces pharmacy compounding.
5. A reformulated product supported by a 505(b)(2) application and formulation patents.

What is propylthiouracil used for and how is it regulated?

Propylthiouracil inhibits thyroid peroxidase and reduces peripheral conversion of thyroxine, or T4, to triiodothyronine, or T3. In the United States, it is used for hyperthyroidism, including Graves' disease, and in selected thyroid-storm situations.

The FDA-approved oral product is generally a 50 mg tablet. Dosing is clinically variable and may require multiple daily administrations, particularly during initial treatment or thyroid storm. The FDA labeling includes a boxed warning for severe liver injury, including hepatic failure and death. PTU is also used preferentially during the first trimester of pregnancy when an antithyroid drug is required, with many clinical guidelines recommending a transition to methimazole later in pregnancy because of PTU liver toxicity concerns (U.S. Food and Drug Administration [FDA], 2020; Ross et al., 2016).

FDA regulatory profile

Attribute	Propylthiouracil position
Active ingredient	Propylthiouracil
Primary route	Oral
Established dosage form	Immediate-release tablet
Common U.S. strength	50 mg
Drug category	Antithyroid agent
U.S. regulatory pathway	Legacy NDA and abbreviated generic products
Controlled-substance status	Not controlled
Boxed warning	Severe liver injury
Pediatric formulation	Primarily compounded or specialty-sourced liquid products
Biosimilar pathway	Not applicable
Core product patent risk	Low for the mature active ingredient
Main commercial barriers	Small market, safety warning, clinical preference for methimazole, manufacturing economics

PTU is not a biologic, so biosimilar competition does not apply. Competition comes from generic tablets, methimazole, radioactive iodine, surgery, and compounded formulations.

What excipients are used in propylthiouracil tablets?

Commercial PTU tablets use conventional pharmaceutical excipients such as diluents, binders, disintegrants, lubricants, glidants, and coating materials. Exact formulations vary by manufacturer and may change over time. The product label and current package insert are the controlling sources for a marketed product's inactive ingredients.

Typical excipient functions include:

Excipient function	Candidate materials	Strategic purpose
Diluent	Lactose, microcrystalline cellulose, dibasic calcium phosphate, mannitol	Tablet mass and manufacturability
Binder	Povidone, pregelatinized starch, hydroxypropyl cellulose	Granule strength and content uniformity
Disintegrant	Crospovidone, sodium starch glycolate, croscarmellose sodium	Rapid tablet breakup
Lubricant	Magnesium stearate, stearic acid	Ejection and tooling protection
Glidant	Colloidal silicon dioxide	Powder flow
Film former	Hypromellose, polyvinyl alcohol	Appearance, handling, moisture protection
Plasticizer	Polyethylene glycol, triacetin	Coating flexibility
Opacifier or colorant	Titanium dioxide or approved colorants	Product identification and light protection
Suspension vehicle	Water, glycerin, sorbitol, cellulose polymers	Liquid dosing and physical stability
Preservative	Depending on formulation and container system	Microbial control in multidose liquids
Taste masker	Ion-exchange resin, lipid coating, polymer barrier	Improved pediatric acceptability

For a new formulation, excipient selection should focus on chemical stability, uniformity at low doses, microbiological control, palatability, and compatibility with the intended regulatory pathway. The Inactive Ingredient Database is a key screening tool for prior FDA exposure by route and dosage form (FDA, 2023a).

What excipient strategy is most attractive for propylthiouracil?

Ready-to-use oral suspension

A liquid PTU formulation has the clearest unmet-use-case potential. Children, pregnant patients with severe nausea, elderly patients, and patients with dysphagia may be unable to use tablets. A commercial suspension could reduce reliance on extemporaneous compounding.

The formulation would need to address:

• Dose uniformity after shaking.
• Sedimentation and redispersibility.
• Chemical stability over the proposed shelf life.
• Microbial control.
• Syringe compatibility.
• Taste masking.
• Accurate delivery at low and intermediate doses.
• Container closure performance.

A 10 mg/mL suspension would allow a 50 mg dose to be administered in 5 mL. A 20 mg/mL product would reduce volume but increase taste and dose-measurement sensitivity. The commercial choice depends on target populations, dose ranges, and the ability to maintain uniformity across the container.

A preservative-free unit-dose suspension could target hospitals and specialty pharmacies. A preserved multidose bottle would be less expensive to manufacture but would face greater palatability and excipient-tolerability considerations.

Taste-masked pediatric formulation

PTU has an inherently difficult taste profile because of its sulfur-containing chemical structure and high active-ingredient exposure in the mouth. Simply adding sweetener may not be sufficient. More credible approaches include:

• Polymer-coated drug particles.
• Ion-exchange resin complexes.
• Lipid-based barriers.
• Multiparticulate granules in a sprinkle product.
• Flavor systems combined with viscosity control.
• pH adjustment that reduces immediate taste release without compromising stability.

The strongest formulation claims would connect taste masking with measurable performance, such as reduced in vitro release in simulated saliva followed by rapid release under gastrointestinal conditions. Human palatability studies would strengthen the commercial case but would not automatically create patentable subject matter.

Orally disintegrating or dispersible tablet

An orally disintegrating tablet could serve patients with dysphagia while avoiding the manufacturing complexity of a liquid. The main technical issue is that PTU dosing often requires more than one tablet or variable dosing. A 50 mg product could be designed for rapid oral dispersion, but the formulation must avoid excessive friability, moisture sensitivity, and unpleasant mouthfeel.

Mannitol, crospovidone, low-substituted hydroxypropyl cellulose, and taste-masking technologies are plausible development components. A dispersible tablet that is intended to be mixed with water would require validated dispersion uniformity and instructions that minimize dose loss.

Low-excipient formulation

Some patients and prescribers favor products with fewer excipients, particularly when a formulation is used chronically. A low-excipient tablet can be positioned for:

• Lactose-intolerant patients.
• Patients avoiding certain colorants.
• Institutional formularies seeking simplified inactive-ingredient profiles.
• Pharmacists managing excipient-related substitutions.

This is a narrower opportunity than a liquid or taste-masked product. Low-excipient claims alone are usually weak unless linked to a measurable manufacturing, stability, dissolution, or tolerability benefit.

What patents could protect a new propylthiouracil formulation?

The active ingredient is old, and broad composition-of-matter protection is not a realistic strategy. A new product would need narrow formulation, manufacturing, or use claims.

Potential patent claim categories

Claim category	Possible protected subject matter	Commercial strength
Suspension composition	PTU concentration, vehicle, viscosity range, preservative system	Moderate if stability is difficult to reproduce
Taste masking	Coated particles, resin complex, release profile, sensory performance	Moderate to strong if supported by comparative data
Multiparticulates	PTU pellets, granules, sprinkle dosage form	Moderate
ODT or dispersible tablet	Porosity, disintegration, low friability, dissolution	Low to moderate
Manufacturing process	Granulation, coating, drying, particle engineering	Moderate if process is essential to performance
Container closure	Light-protective or moisture-barrier packaging	Usually limited
Method of use	Administration to a defined patient subgroup	Narrow and vulnerable to design-around
Combination therapy	PTU with a specific adjunct or dosing regimen	Potentially stronger, but clinically complex

A formulation patent should include composition ranges, critical quality attributes, stability data, dissolution data, taste-masking evidence, and comparative performance against an immediate-release tablet or compounded suspension.

Patent term would generally run 20 years from the earliest effective nonprovisional filing date, subject to patent-term adjustment and any applicable regulatory extension. No current broad PTU compound patent should be assumed to block generic or reformulated entry. A current patent search and Orange Book review would be required before relying on a specific patent position.

What is the Orange Book status of propylthiouracil?

PTU's Orange Book position is primarily relevant to approved product listings and any patents submitted for applicable NDA products. Because the active ingredient and conventional tablet are longstanding products, the principal commercial constraint is not an active ingredient patent barrier.

A reformulated PTU product could have a different Orange Book strategy depending on the approval pathway:

Development route	Likely use
ANDA	Tablet equivalent to a reference product
505(b)(2) NDA	New suspension, dispersible tablet, ODT, or other differentiated dosage form
Full NDA	Unlikely unless the sponsor makes a substantial new clinical claim
Suitability petition	Potentially relevant only if the proposed difference fits FDA requirements

An ANDA may permit certain inactive-ingredient differences if the product remains pharmaceutically equivalent, bioequivalent, and acceptable from a safety standpoint. A materially different dosage form, liquid formulation, new route, or clinical positioning generally creates a stronger 505(b)(2) rationale (FDA, 2019).

When does propylthiouracil lose exclusivity?

Conventional PTU tablets have already lost practical market exclusivity. Generic products are available, and the drug has no biosimilar protection period because it is a small molecule.

The relevant exclusivity question applies to a new formulation, not to PTU itself. A 505(b)(2) product could potentially obtain:

• Three years of marketing exclusivity for certain new clinical investigations essential to approval.
• Five-year new chemical entity exclusivity only if the product qualifies as a new active ingredient, which PTU would not.
• Orphan-drug exclusivity only for a qualifying orphan indication, subject to FDA designation and approval requirements.
• Pediatric exclusivity only under a qualifying FDA Written Request and statutory conditions.

A new formulation patent could provide protection beyond regulatory exclusivity, but its value would depend on claim breadth and the ability of competitors to launch a conventional tablet or alternative suspension.

Which companies are challenging propylthiouracil?

PTU competition is fragmented among generic drug manufacturers, contract manufacturers, compounding pharmacies, and hospitals. The competitive field changes with supply contracts and product discontinuations. The primary commercial competitors are:

• Generic manufacturers supplying 50 mg tablets.
• Methimazole manufacturers.
• Compounding pharmacies supplying oral suspensions.
• Hospital pharmacies preparing patient-specific liquid doses.
• Thyroid-specialty products using alternative treatment modalities.

No major biosimilar challenge exists. Paragraph IV litigation is not a central current feature of the established PTU tablet market because the product is old and genericized. Paragraph IV risk would become relevant if a sponsor launched a newly patented PTU suspension or other reformulated product and a later ANDA applicant challenged its listed patents.

What patent litigation and settlement risks affect PTU?

The conventional tablet market has low expected patent-litigation exposure. A differentiated formulation would create a different risk profile.

Key risks include:

1. Obviousness challenges. A competitor may argue that combining known suspending agents, sweeteners, preservatives, or coating polymers was routine.
2. Enablement attacks. Broad claims covering many vehicles or taste-masking systems may lack support across the full scope.
3. Design-around risk. Competitors could use a different resin, polymer, concentration, flavor system, or container.
4. Reference-product substitution. A generic tablet could remain available even if a new liquid formulation is protected.
5. Compounding competition. A pharmacy may prepare a suspension where permitted by state and federal law, limiting the price premium for a commercial product.
6. Settlement timing. Any ANDA settlement would depend on the asserted formulation patents and the first-filer structure, not on PTU's historical status.

The most defensible claims would protect a demonstrated technical result that is difficult to reproduce without using the claimed formulation architecture.

What FDA and manufacturing barriers affect a PTU suspension?

A liquid product faces higher development and quality risks than a conventional tablet. The sponsor must establish:

• Assay and degradation-product limits.
• Uniformity throughout bottle use.
• Redispersibility after storage.
• Microbial limits or preservative effectiveness.
• In-use stability after opening.
• Dosing-device accuracy.
• Compatibility with oral syringes and feeding tubes, if claimed.
• Extractables and leachables for the container system.
• Transport stability.
• Acceptable taste and mouthfeel.

PTU's liver warning does not create a direct excipient requirement, but it raises the importance of clear labeling, dosing accuracy, and avoidance of formulation variability. A liquid that produces inconsistent dosing would have a weak clinical and regulatory profile.

Manufacturing economics also matter. PTU is inexpensive, so a product cannot rely on active-ingredient value to absorb high production costs. The formulation should use conventional equipment, high-throughput filling, and readily sourced excipients. A specialty product can command a higher price only if it reduces compounding labor, improves adherence, or fills an institutional supply gap.

How does propylthiouracil compare with methimazole?

Factor	Propylthiouracil	Methimazole
Usual role	Selected hyperthyroidism and thyroid storm use	Preferred routine antithyroid therapy in many patients
Pregnancy positioning	Often preferred during first trimester when needed	Often preferred after first trimester
Liver risk	Major boxed-warning concern	Lower severe hepatotoxicity concern relative to PTU
Dosing	Often multiple daily doses	Often once or multiple daily doses depending on regimen
Pediatric liquid opportunity	Meaningful	Also meaningful
Generic competition	Mature	Mature
Patent opportunity	Formulation-led	Formulation-led
Commercial scale	Narrower	Generally broader

PTU's commercial opportunity is therefore concentrated in cases where its clinical role is differentiated. A sponsor should avoid positioning a new excipient system as a broad replacement for methimazole. The more credible position is improved delivery for patients who already require PTU.

What revenue exposure and commercial opportunities exist?

Standalone PTU revenue is unlikely to match major endocrine products because the active ingredient is generic, the patient population is limited, and methimazole is commonly used for routine therapy. Public companies generally do not report PTU revenue separately, so product-level revenue estimates should not be inferred from corporate filings.

Commercial opportunities are strongest in the following channels:

Opportunity	Buyer	Revenue logic
Ready-to-use suspension	Retail, specialty pharmacy, pediatric clinics	Replaces compounding and improves convenience
Hospital unit-dose liquid	Hospitals and health systems	Reduces pharmacy preparation and dosing errors
Taste-masked pediatric product	Caregivers and pediatric prescribers	Supports adherence and repeat use
Dysphagia formulation	Elderly and medically complex patients	Addresses tablet administration barrier
Reliable tablet supply	Wholesalers and formularies	Gains share through availability rather than premium science
Private-label or contract manufacturing	Specialty pharma companies	Lower commercial investment and faster market access
Global licensing	Regional pharmaceutical firms	Uses local registration and distribution networks

The most attractive business model may be licensing a formulation platform to a specialty generic company rather than building a large direct commercial organization.

What geographic markets offer the best opportunity?

The United States offers the clearest 505(b)(2), hospital, and specialty-pharmacy opportunity. Europe and other regulated markets may support differentiated oral liquids, but regulatory requirements, reference-product rules, and pricing controls differ by country.

Emerging markets may have larger unmet needs for pediatric liquids and stable supply, but pricing pressure is greater. Local manufacturing or licensing may be required. Geographic patent value would depend on filing before public disclosure and on whether the formulation claims meet local novelty and inventive-step standards.

A global strategy should prioritize:

1. U.S. formulation development and regulatory positioning.
2. European and selected Commonwealth markets with established pediatric liquid demand.
3. Licensing in countries where local manufacturing improves tender access.
4. Hospital and specialty-pharmacy channels before broad retail expansion.

Key Takeaways

• PTU's conventional tablet market is mature and largely generic.
• The active ingredient offers little realistic new-molecule patent opportunity.
• A ready-to-use oral suspension is the strongest excipient-led commercial concept.
• Taste masking, dose uniformity, microbiological stability, and container compatibility are the key technical issues.
• A materially differentiated liquid or dispersible product would likely fit a 505(b)(2) strategy better than a conventional ANDA.
• Formulation patents should rely on measurable performance, not broad lists of common excipients.
• Paragraph IV and litigation exposure are limited for existing tablets but could become significant for a patented reformulation.
• Methimazole limits PTU's overall market size, while PTU's pregnancy and thyroid-storm roles create focused niches.
• Hospital supply, pediatric dosing, dysphagia, and compounding replacement are the most credible commercial segments.
• No biosimilar pathway applies.

FAQs

Can propylthiouracil be formulated as a commercially manufactured oral liquid?

Yes. A commercial liquid would need validated dose uniformity, stability, microbial control, redispersibility, palatability, and dosing-device accuracy. Its regulatory pathway would likely depend on the extent of formulation and labeling differences from approved tablets.

Which excipients are most useful for masking propylthiouracil taste?

Polymer-coated particles, ion-exchange resin complexes, lipid barriers, and multiparticulate systems are more technically credible than sweeteners alone. The preferred system must preserve gastrointestinal release and chemical stability.

Is propylthiouracil eligible for biosimilar competition?

No. PTU is a small-molecule drug. Competition occurs through generic drug applications, reformulations, compounding, and alternative antithyroid therapies.

Can a new PTU suspension receive three-year FDA exclusivity?

Potentially, if the sponsor obtains approval based on new clinical investigations that were essential to approval and satisfy statutory requirements. A routine reformulation without qualifying clinical work would not automatically receive three-year exclusivity.

Does a new excipient create patent protection by itself?

No. Patentability generally depends on the claimed formulation, technical effect, novelty, non-obviousness, and supporting evidence. The use of a familiar excipient in a predictable role is vulnerable to an obviousness challenge.

References

1. American Thyroid Association. (2016). 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid, 26(10), 1343-1421.

2. DailyMed. (2024). Propylthiouracil tablet prescribing information. U.S. National Library of Medicine.

3. Ross, D. S., Burch, H. B., Cooper, D. S., Greenlee, M. C., Laurberg, P., Maia, A. L., Rivkees, S. A., Samuels, M., Sosa, J. A., Stan, M. N., & Walter, M. A. (2016). 2016 American Thyroid Association guidelines for diagnosis and management of hyperthyroidism and other causes of thyrotoxicosis. Thyroid, 26(10), 1343-1421.

4. U.S. Food and Drug Administration. (2019). Applications covered by section 505(b)(2). FDA.

5. U.S. Food and Drug Administration. (2020). Propylthiouracil tablets: Prescribing information and boxed warning. FDA.

6. U.S. Food and Drug Administration. (2023a). Inactive Ingredient Database. FDA.

7. U.S. Food and Drug Administration. (2023b). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.