CYTOMEL Drug Patent Profile

When do Cytomel patents expire, and what generic alternatives are available?

Cytomel is a drug marketed by King Pharms and is included in one NDA.

The generic ingredient in CYTOMEL is liothyronine sodium. There is one drug master file entry for this compound. Nineteen suppliers are listed for this compound. Additional details are available on the liothyronine sodium profile page.

DrugPatentWatch^® Litigation and Generic Entry Outlook for Cytomel

A generic version of CYTOMEL was approved as liothyronine sodium by XGEN PHARMS on August 17^th, 2005.

Summary for CYTOMEL

US Patents:	0
Applicants:	1
NDAs:	1
Finished Product Suppliers / Packagers:	2
Raw Ingredient (Bulk) Api Vendors:	72
Clinical Trials:	12
Patent Applications:	1,516
Drug Prices:	Drug price information for CYTOMEL
Drug Sales Revenues:	Drug sales revenues for CYTOMEL
What excipients (inactive ingredients) are in CYTOMEL?	CYTOMEL excipients list
DailyMed Link:	CYTOMEL at DailyMed

See drug prices for CYTOMEL

See drug sales revenues for CYTOMEL

Recent Clinical Trials for CYTOMEL

Identify potential brand extensions & 505(b)(2) entrants

Sponsor	Phase
Virginia Commonwealth University	Phase 2
Oregon Health and Science University	Phase 1
Johns Hopkins University	Phase 1

See all CYTOMEL clinical trials

Pharmacology for CYTOMEL

Drug Class

l-Triiodothyronine

US Patents and Regulatory Information for CYTOMEL

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
King Pharms	CYTOMEL	liothyronine sodium	TABLET;ORAL	010379-001	Approved Prior to Jan 1, 1982	AB	RX	Yes	No
King Pharms	CYTOMEL	liothyronine sodium	TABLET;ORAL	010379-002	Approved Prior to Jan 1, 1982	AB	RX	Yes	No
King Pharms	CYTOMEL	liothyronine sodium	TABLET;ORAL	010379-003	Approved Prior to Jan 1, 1982	AB	RX	Yes	No

Cytomel Market Dynamics, Patent Status, Generic Competition, and Financial Trajectory

Last updated: October 5, 2026

Cytomel is the branded form of liothyronine sodium, a synthetic T3 thyroid hormone. Its commercial position is mature and largely genericized. Pfizer retains the U.S. brand, but Cytomel has no meaningful market exclusivity, no disclosed standalone revenue, and limited pricing power. The product’s value is supported by clinical familiarity, physician demand for T3 therapy, and a relatively constrained generic market rather than by patent protection.

What is Cytomel and how is it regulated?

Cytomel contains liothyronine sodium, the synthetic sodium salt of triiodothyronine. It is approved for thyroid hormone replacement in hypothyroidism and for selected thyroid suppression uses. The product is administered orally in tablet strengths that include 5 mcg, 25 mcg, and 50 mcg, subject to market availability and labeling.

The U.S. product is associated with FDA NDA 006542. Pfizer Laboratories is identified as the distributor of the branded product in U.S. prescribing information. FDA labeling warns that liothyronine has a narrow therapeutic margin and that excessive dosing can produce cardiovascular and skeletal adverse effects.[1]

Item	Cytomel status
Active ingredient	Liothyronine sodium
Therapeutic class	Thyroid hormone
Dosage form	Immediate-release oral tablet
U.S. brand holder/distributor	Pfizer Laboratories
FDA application	NDA 006542
Regulatory pathway	Legacy new drug application
Exclusivity position	No current regulatory exclusivity expected
Competitive products	FDA-approved generic liothyronine sodium tablets
Biosimilar exposure	None; Cytomel is a small-molecule drug

When does Cytomel lose exclusivity?

Cytomel lost practical market exclusivity decades ago. Its active ingredient, liothyronine sodium, is an established small molecule with generic equivalents approved through abbreviated new drug applications. The product does not depend on a current New Chemical Entity exclusivity period, orphan-drug exclusivity period, pediatric exclusivity period, or other modern regulatory protection.

The commercial effect is important: generic manufacturers can compete on the same active ingredient and dosage form without reproducing Pfizer’s brand investment. Cytomel therefore competes primarily through brand recognition, supply reliability, physician familiarity, and patient continuity.

Unlike newer thyroid products, Cytomel does not have a meaningful exclusivity runway that could support a near-term revenue step-up. Its financial trajectory is mature to declining in branded terms, with residual demand coming from patients and prescribers who prefer the branded product.

What patents protect Cytomel?

Cytomel’s core composition-of-matter protection is expired. Liothyronine sodium is an old active pharmaceutical ingredient, and the basic drug substance cannot provide a current patent barrier.

What formulation patents cover Cytomel?

No currently material formulation patent estate is publicly associated with Cytomel’s conventional immediate-release tablets. The product does not rely on a recently developed extended-release delivery system, transdermal platform, implant, or other proprietary formulation that would create a new patent-based market barrier.

Any historical manufacturing, formulation, or process patents would not normally preserve meaningful exclusivity for a legacy immediate-release tablet after generic approval. The relevant competitive question is whether an active Orange Book-listed patent blocks an approved generic product. Cytomel does not appear to have a current patent position comparable to recently launched branded medicines with multiple listed formulation or method-of-use patents.[2]

What method-of-use patents cover liothyronine?

The principal uses of liothyronine are longstanding thyroid replacement and suppression indications. These indications are clinically established and generally vulnerable to generic competition. A method-of-use patent would need to cover a narrow, enforceable indication and be listed or asserted in a manner that could delay generic competition. No publicly disclosed, commercially significant Cytomel method-of-use estate is evident in the principal FDA and Pfizer materials reviewed for this analysis.

What is the Orange Book status of Cytomel?

The Orange Book treats approved generic liothyronine sodium products as therapeutically competitive alternatives to the reference listed drug when the relevant dosage strength and product requirements are met. The practical Orange Book position is therefore generic substitution and abbreviated approval, not brand exclusivity.

Orange Book issue	Commercial implication
Reference listed drug	Cytomel
Generic pathway	ANDA approval
Patent-based delay	No material current delay identified
Substitution	Depends on state pharmacy law and product rating
Brand premium	Supported by preference and continuity, not exclusivity
Paragraph IV relevance	Limited after broad generic availability

An Orange Book listing does not itself guarantee pharmacy substitution. Substitution depends on the generic product’s therapeutic equivalence rating, state law, payer policy, and prescriber instructions.

Which companies are challenging Cytomel?

Cytomel has already faced the principal form of competitive challenge: approval and commercialization of generic liothyronine sodium tablets. The market is not defined by a current high-profile Paragraph IV campaign against a protected product. It is defined by long-standing generic availability.

A Paragraph IV certification can challenge an asserted patent during an ANDA review. For Cytomel, the absence of a meaningful current patent barrier reduces the commercial value of a new Paragraph IV challenge. Generic applicants can compete through ordinary ANDA pathways where no blocking patent remains.

Publicly disclosed materials do not identify a major current Cytomel patent settlement that would materially postpone generic entry. Any historical ANDA disputes would have limited strategic importance unless they affected a specific dosage strength, supplier, or manufacturing process.

What is the FDA regulatory status of Cytomel?

Cytomel remains an FDA-approved prescription thyroid hormone product. The central regulatory issues are dosing precision, potency, stability, and safety rather than clinical efficacy against a new disease target.

Liothyronine has a narrower therapeutic window than levothyroxine in practical use because small dose changes can produce clinically relevant changes in thyroid hormone exposure. FDA labeling identifies risks associated with overtreatment, including cardiac effects and bone loss.[1]

The regulatory profile creates operational value for a reliable manufacturer. Patients stabilized on a particular product may experience concern over tablet appearance, excipients, strength availability, or potency consistency after switching. That factor supports some brand retention even when generic products are legally substitutable.

How strong is the Cytomel patent estate?

Cytomel’s patent estate is weak as a source of exclusivity but stronger as a legacy brand position.

Estate component	Assessment
Composition-of-matter patent	Expired
Core tablet formulation	Mature and vulnerable to generic replication
Delivery-system patents	No material current Cytomel platform identified
Method-of-use patents	No publicly material current estate identified
Manufacturing know-how	Potentially relevant to quality and supply, not market exclusivity
Trademark and brand	Provides commercial recognition but not generic blocking rights
Regulatory exclusivity	No current meaningful period identified

The remaining defensibility is operational. Pfizer can benefit from established manufacturing controls, distribution relationships, brand recognition, and patient continuity. Those advantages do not prevent generic entry and are vulnerable to payer substitution.

How does Cytomel compare with levothyroxine?

Cytomel occupies a smaller and more specialized segment than levothyroxine. Levothyroxine is the standard first-line thyroid replacement product for most patients with hypothyroidism. Liothyronine is used selectively because of its shorter half-life, faster onset of pharmacologic effect, and greater sensitivity to dose changes.

Factor	Cytomel	Levothyroxine products
Hormone	T3	T4
Standard use	Selected replacement or combination therapy	Broad first-line replacement
Generic competition	Established	Extensive
Patient population	Smaller	Much larger
Dosing sensitivity	High	High, but generally more stable
Brand differentiation	Familiarity and continuity	Formulation, stability, and brand preference
Revenue ceiling	Limited	Larger due to population size

Cytomel benefits from demand that is not fully interchangeable from a clinical or patient-preference perspective. It does not, however, have the volume base or broad treatment position of levothyroxine.

What generic entry risks exist for Cytomel?

Generic entry is already a structural feature of the market. The remaining risks concern share migration and price erosion rather than a future first generic launch.

Generic erosion scenarios

Scenario	Likely effect on Cytomel
Stable generic supply	Gradual branded share erosion and payer substitution
Generic shortage	Temporary recovery in brand demand or price leverage
Additional generic suppliers	Greater price compression
Payer mandate for generic use	Faster conversion from brand
Product discontinuation or supply disruption	Potential loss of prescriber and patient confidence
New T3 formulation	Possible niche displacement, but no established near-term threat

Liothyronine is a relatively small market, which can limit the number of manufacturers willing to maintain production. That constraint may support brand demand during shortages. It can also increase volatility if a supplier experiences manufacturing, quality, or inventory problems.

What manufacturing and intellectual-property barriers affect Cytomel?

The main barriers are technical and operational rather than legal. Liothyronine tablets require accurate low-dose content uniformity, reliable stability, controlled potency, and consistent dissolution performance. These requirements are important because tablet strengths are measured in micrograms and dosing errors can have clinically significant consequences.

Manufacturing know-how can therefore support a supplier’s position. It does not normally create durable exclusivity once multiple ANDA-approved products are available. The critical commercial asset is dependable supply across low-dose strengths, not a proprietary patent platform.

Supply concentration can create temporary pricing opportunities for the brand. Those opportunities are episodic and should not be valued as a durable replacement for patent protection.

What litigation affects Cytomel?

No major active patent litigation involving Cytomel is identified in the principal publicly available FDA and Pfizer materials used for this review. The product’s litigation risk is lower than that of a recently launched branded medicine with an active Orange Book patent portfolio.

Potential disputes would more likely involve:

• Product liability or adverse-event claims.
• Manufacturing or quality allegations.
• Generic substitution or labeling issues.
• Contract and distribution matters.
• Shortage-related commercial disputes.

No publicly disclosed settlement agreement appears to create a material delay in generic access to liothyronine sodium tablets.

What are Cytomel’s licensing deals?

Cytomel’s commercial history includes corporate ownership and portfolio transfers associated with Pfizer’s acquisition of King Pharmaceuticals. Pfizer completed its acquisition of King in 2011, bringing King’s products into Pfizer’s portfolio.[3] Public financial reporting does not identify a current, material third-party licensing arrangement that separately drives Cytomel economics.

Cytomel is not reported as a standalone revenue line in Pfizer’s annual reports. Its sales are aggregated within broader pharmaceutical reporting categories, and Pfizer does not disclose product-level revenue, gross margin, or operating profit for Cytomel.[4]

What is Cytomel’s financial trajectory?

Cytomel’s financial trajectory is best characterized as mature, low-growth, and supply-sensitive.

Financial driver	Direction
Unit demand	Stable to modestly declining in branded channel
Brand share	Downward pressure from generics
Net price	Limited; payer and generic pressure
Gross margin	Likely favorable relative to manufacturing cost, but undisclosed
Revenue disclosure	No standalone public figure
Growth catalyst	Supply disruption, brand preference, or new formulation
Principal risk	Generic substitution and portfolio deprioritization

The brand can remain economically useful even at modest sales levels because an old tablet product may require less commercial investment than a new specialty medicine. Its value is constrained by the absence of exclusivity and the availability of generic alternatives.

Revenue exposure to Pfizer is therefore likely immaterial at the consolidated-company level. Pfizer reported tens of billions of dollars in annual pharmaceutical revenue, while Cytomel is not separately identified as a material product in its public segment reporting.[4] A precise Cytomel revenue estimate would require prescription, channel, and net-price data that Pfizer does not disclose.

What is the competitive outlook for Cytomel?

The competitive outlook is stable but defensive. The product is unlikely to generate meaningful organic growth without a new delivery format, new indication, or supply disruption affecting generic competitors.

The most plausible commercial outcomes are:

1. Continued brand erosion with persistent residual demand.
2. Stable niche sales from prescribers and patients who prefer Cytomel.
3. Temporary brand gains during generic shortages.
4. Gradual portfolio rationalization if Pfizer reduces investment in mature products.
5. Limited strategic value unless paired with a differentiated T3 formulation.

Biosimilars are irrelevant because Cytomel is a chemically synthesized small molecule. The relevant threat is generic substitution, not biologic interchangeability.

Key Takeaways

• Cytomel is Pfizer’s branded liothyronine sodium tablet and has a mature FDA-approved profile.
• Core patent protection and practical regulatory exclusivity expired long ago.
• Generic liothyronine sodium products define the competitive market.
• No material current Cytomel formulation or method-of-use patent estate is publicly identified.
• Paragraph IV litigation and settlement activity do not appear to be current market drivers.
• Pfizer does not disclose standalone Cytomel revenue, profit, or forecast data.
• The brand’s residual value comes from physician familiarity, patient continuity, and supply reliability.
• Financial performance is likely mature and supply-sensitive, with limited pricing power.
• Manufacturing precision and consistent low-dose supply matter more than intellectual-property protection.
• Cytomel has no biosimilar risk; generic substitution is the central competitive risk.

FAQs About Cytomel Market Dynamics

Is Cytomel still patent protected?

No material current patent protection appears to block generic liothyronine sodium tablet competition. The core active ingredient and legacy tablet technology are long established.

Does Cytomel have FDA exclusivity?

Cytomel does not appear to have a current NCE, orphan, pediatric, or other meaningful regulatory exclusivity period.

Is Cytomel being discontinued?

Public FDA and Pfizer materials do not establish a general discontinuation of Cytomel. Product availability can vary by strength, channel, and inventory conditions.

Who manufactures generic liothyronine sodium?

Multiple manufacturers have received FDA approval for generic liothyronine sodium products over time. Manufacturer participation and availability can vary by dosage strength and market conditions.[2]

Could a new liothyronine formulation replace Cytomel?

A sustained-release or otherwise differentiated T3 formulation could compete for a niche, but it would require FDA approval, clinical support, manufacturing scale, and payer adoption. No such product currently defines the Cytomel market.

References

1. Pfizer Laboratories. (2023). Cytomel (liothyronine sodium) tablets: U.S. prescribing information. Pfizer Inc. https://labeling.pfizer.com
2. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/
3. Pfizer Inc. (2011). Pfizer completes acquisition of King Pharmaceuticals. https://www.pfizer.com/news/press-release
4. Pfizer Inc. (2024). Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934. https://investors.pfizer.com/financials/annual-reports/default.aspx

DrugChatter Q&A for CYTOMEL

Cytomel pharmacie?