Sponsor	Phase
The University of Hong Kong	Phase 2
Karolinska Institutet	Phase 2
Kristina Gemzell Danielsson	Phase 2

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Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Bioenvision	MODRASTANE	trilostane	CAPSULE;ORAL	018719-001	Dec 31, 1984		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
Bioenvision	MODRASTANE	trilostane	CAPSULE;ORAL	018719-002	Dec 31, 1984		DISCN	No	No	⤷ Start Trial	⤷ Start Trial				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Exclusivity Expiration

Last updated: September 4, 2026

Trilostane is a mature veterinary endocrine drug with stable recurring demand, limited patent protection, and modest disclosure of product-level financial performance. Dechra Pharmaceuticals’ Vetoryl brand remains the primary U.S. commercial product for canine hyperadrenocorticism, while compounded and off-label products create price competition. The asset’s value depends on chronic treatment duration, veterinary monitoring, brand trust, and distribution rather than exclusivity from active composition patents.

Trilostane Market Dynamics, Patent Position, FDA Status, and Financial Trajectory

Trilostane inhibits adrenal steroid synthesis and is used mainly to manage hyperadrenocorticism, commonly called Cushing’s syndrome, in dogs. The drug is marketed in the United States as Vetoryl capsules by Dechra Pharmaceuticals. It is also used in veterinary medicine outside the United States and has historical human-use precedent, but it is not an FDA-approved human drug.

The commercial profile differs from a conventional human pharmaceutical. Trilostane has no meaningful U.S. human Orange Book franchise, no current human Paragraph IV litigation market, and no apparent composition-of-matter exclusivity. Its economic durability comes from recurring veterinary prescriptions, chronic disease management, and the limited number of approved canine endocrine therapies.

What is trilostane used for and who markets it?

Trilostane is an adrenal steroidogenesis inhibitor. In dogs, it is used to control pituitary-dependent and adrenal-dependent hyperadrenocorticism. Vetoryl is approved for the control of hyperadrenocorticism in dogs caused by pituitary- or adrenal-dependent disease [1].

Item	Current commercial position
Active ingredient	Trilostane
Principal U.S. brand	Vetoryl
U.S. sponsor	Dechra Pharmaceuticals PLC
U.S. regulator	FDA Center for Veterinary Medicine
U.S. dosage form	Oral capsules
Approved U.S. species	Dogs
Primary indication	Canine hyperadrenocorticism
Human FDA approval	None identified
Orange Book listing	Not applicable as a human drug
Main alternatives	Mitotane, compounded trilostane, specialty veterinary products
Treatment pattern	Chronic, often lifelong administration with laboratory monitoring

The FDA approved Vetoryl under New Animal Drug Application No. 141-291. The product was initially approved in capsule strengths that included 10 mg, 30 mg, 60 mg, and 120 mg. Product labeling has been updated over time, including warnings related to hypoadrenocorticism, renal disease, liver disease, and drug monitoring [1].

What is the FDA regulatory status of trilostane?

Vetoryl is FDA-approved for veterinary use in dogs. Trilostane is not approved by the FDA for human Cushing’s syndrome, oncology, or other human indications.

The U.S. regulatory distinction matters commercially:

Vetoryl is an approved animal drug.
Human generic-drug rules and Orange Book patent certifications do not govern the product.
Generic veterinary competition proceeds through animal-drug pathways, including abbreviated applications where available, rather than the standard human ANDA Paragraph IV framework.
Compounded trilostane is distributed through veterinary compounding channels and does not have the same regulatory status as Vetoryl.

FDA labeling requires dose adjustment and monitoring. Veterinary clinicians generally evaluate clinical response and monitor cortisol-related laboratory measures, electrolytes, renal function, liver function, and signs of excessive adrenal suppression. These monitoring requirements support recurring veterinary service revenue but also limit treatment to cases where owners can sustain diagnostic and medication costs [1].

When does trilostane lose exclusivity?

Trilostane’s underlying chemical and therapeutic exclusivity expired long ago. The compound was developed decades before the current commercial Vetoryl franchise and has historical use in human medicine outside the United States. No active composition-of-matter patent is understood to protect the commercial molecule in the United States.

Vetoryl’s U.S. commercial protection therefore does not rest on a current basic-molecule patent. Potential barriers are more likely to involve:

FDA approval status and regulatory compliance.
Manufacturing controls and product quality.
Veterinary distribution relationships.
Brand recognition among veterinarians.
Capsule strength and packaging economics.
Clinical monitoring and prescriber familiarity.
Product-specific formulation or manufacturing rights, if any remain enforceable in a particular jurisdiction.

The precise expiration of historical trilostane patents is not commercially material to the current U.S. market because those patents are outside their enforceable terms. No current human patent-expiration date should be used to model Vetoryl revenue loss.

What patents protect trilostane and Vetoryl?

No current U.S. Orange Book patent estate protects Vetoryl because Vetoryl is an animal drug rather than an FDA-approved human drug. The core trilostane compound is old, and basic compound patents are expired.

Potential intellectual-property protection can still arise from:

Specific veterinary formulations.
Manufacturing processes.
Capsule composition.
Stability improvements.
New dosing regimens.
Combination treatments.
Delivery systems.
Country-specific applications.

The commercial record does not establish a broad, active U.S. patent estate comparable to those supporting newer human specialty drugs. Any patent review should distinguish between:

IP category	Relevance to trilostane
Composition of matter	Historical and expired
Human Orange Book patents	Not applicable
Animal-drug product patents	Potentially relevant only if listed or enforceable
Formulation patents	Possible but not established as a broad market barrier
Method-of-use patents	Limited commercial value without a new protected indication
Manufacturing patents	May protect process know-how but rarely block all supply
Trademark rights	Vetoryl brand protection remains commercially relevant

How many patents cover trilostane?

The commercially relevant answer is that trilostane has no known active U.S. composition-of-matter patent barrier supporting Vetoryl pricing. Patent counts from global databases may include expired compound patents, foreign filings, abandoned applications, family members, formulations, or unrelated steroidogenesis research. Those records should not be counted as active market exclusivity without jurisdiction-specific legal-status review.

For investment and licensing analysis, the relevant patent question is not the number of historical documents. It is whether an enforceable claim can block an approved competing canine product in the target country. The available commercial evidence supports a low patent-strength assessment for the core molecule and a moderate product-quality and regulatory-barrier assessment.

What is the Orange Book status of trilostane?

Trilostane has no human Orange Book status because it is not an FDA-approved human drug. Vetoryl is regulated through the FDA Center for Veterinary Medicine and appears in the FDA animal-drug approval system rather than the human Approved Drug Products with Therapeutic Equivalence Evaluations, commonly called the Orange Book [2].

As a result:

There is no standard Orange Book patent listing for Vetoryl.
There is no conventional human ANDA reference product analysis.
A competitor does not ordinarily launch through a human Paragraph IV certification.
Veterinary generic entry must be assessed under the applicable animal-drug approval pathway.

Which companies are challenging Vetoryl?

The main competitive pressure comes from veterinary compounders and potential animal-drug competitors rather than a conventional human generic-drug litigation campaign.

Compounded trilostane

Veterinary pharmacies compound trilostane into capsules, flavored preparations, suspensions, and other dosage forms. Compounded products may offer lower prices or flexible strengths. They can be attractive for small dogs, large dogs requiring unusual doses, or animals with swallowing difficulties.

The trade-off is that compounded products do not automatically have the same FDA approval, manufacturing controls, bioequivalence evidence, or post-market oversight as Vetoryl. Veterinary prescribers may therefore retain a preference for the approved brand, especially when stable clinical control is more important than acquisition cost.

Approved veterinary competition

Mitotane is the principal pharmacologic alternative for canine hyperadrenocorticism. It works through adrenal cytotoxicity and has a different administration, monitoring, and adverse-effect profile. It is not a direct generic substitute for trilostane, but it limits Vetoryl’s pricing power.

The competitive landscape also includes referral hospitals, endocrine specialists, diagnostic laboratories, and veterinary practices that influence treatment selection. The most important competitive decision is often trilostane versus mitotane, not one branded trilostane product versus another.

What patent litigation affects trilostane?

No major U.S. human patent litigation campaign is associated with Vetoryl or trilostane. There is no established Paragraph IV litigation pattern comparable to branded oncology, diabetes, or biologic products.

Litigation risk is more likely to arise from:

Product-quality claims.
Veterinary adverse-event allegations.
Trademark disputes.
Contract and distribution issues.
Compounding enforcement.
Regulatory disputes involving animal-drug manufacturing.

The absence of major patent litigation reduces legal-cost exposure but also confirms that the product’s commercial defense is based mainly on brand, regulatory status, and supply reliability.

What is the financial trajectory for trilostane?

Dechra has not historically reported Vetoryl revenue as a separately disclosed public segment in the manner of a large human pharmaceutical product. Vetoryl is included within Dechra’s broader companion-animal pharmaceutical business. Dechra became privately held after EQT-backed acquisition completed in 2023, reducing public visibility into current product-level sales and margins [3].

The financial trajectory is best characterized as follows:

Period	Financial interpretation
Early commercial period	Market creation through approval and veterinary adoption
Mature brand period	Recurring chronic-use revenue and broad veterinary distribution
Current period	Stable demand, limited molecule-level exclusivity, increased price pressure
Medium-term outlook	Low-to-moderate growth tied to canine diagnosis and treatment persistence
Downside risk	Compounding, approved veterinary competition, supply interruptions, owner affordability
Upside risk	Higher diagnosis rates, expanded veterinary screening, improved compliance, geographic growth

Vetoryl has several revenue-supporting characteristics:

Treatment is usually chronic rather than episodic.
The target disease is managed rather than cured.
Dose titration creates continuing prescriptions.
Laboratory monitoring generates recurring veterinary visits.
Clinical switching can be undesirable after disease control is achieved.
The product has a recognized brand in a specialized therapeutic category.

The main limitation is market scale. Canine hyperadrenocorticism is important within companion-animal endocrinology but is not a mass-market indication comparable to flea, tick, dermatology, or chronic pain products. Revenue growth is therefore more likely to come from diagnosis, penetration, pricing, and geographic expansion than from a large untreated population.

How strong is the trilostane patent estate?

The patent estate is weak for the active ingredient and moderate for commercial execution.

Factor	Assessment	Commercial effect
Core molecule	Weak patent position	Does not support long-term exclusivity
Regulatory approval	Meaningful barrier	Supports confidence in approved use
Brand recognition	Moderate to strong	Preserves prescribing preference
Manufacturing know-how	Potentially relevant	Can support quality and supply consistency
Clinical switching costs	Moderate	Favors continued use after stabilization
Compounding exposure	High	Creates price and availability pressure
Human patent litigation risk	Low	Limits legal defense costs
Veterinary generic risk	Moderate	Depends on approved competitors and jurisdiction

The product can remain commercially durable despite weak patent protection because recurring veterinary use and clinician trust can persist after patent expiry. That durability should not be confused with legal exclusivity.

What generic launch risks exist for Vetoryl?

The most credible generic-entry scenario is gradual erosion rather than an abrupt U.S. launch event. A competitor would need to establish an approved animal-drug product, meet manufacturing and quality requirements, obtain distribution, and persuade veterinarians to substitute or initiate therapy with the competing product.

Potential launch scenarios include:

Low-price compounded substitution

This is the most immediate source of pressure. It can reduce brand volume in price-sensitive cases, particularly where customized dosing is needed.

Approved generic capsules

An approved competitor could create greater pressure by offering standardized strengths with regulatory support. The impact would depend on availability, wholesaler access, veterinary adoption, and evidence of consistent drug content.

Alternative therapy adoption

Mitotane and other management strategies can limit the addressable market for trilostane, especially in cases where clinicians prefer a different adrenal-control approach.

Supply-driven switching

Shortages or distribution interruptions can produce temporary substitution and weaken brand loyalty. Consistent supply is therefore a material competitive asset.

How does trilostane compare with mitotane?

Attribute	Trilostane	Mitotane
Primary use	Canine hyperadrenocorticism	Canine hyperadrenocorticism
Mechanism	Inhibits adrenal steroid synthesis	Adrenocortical cytotoxic effect
Use pattern	Often chronic daily dosing	Induction and maintenance regimens
Monitoring	Required	Required
Switching	Commonly maintained once controlled	Used when clinically preferred
Commercial competition	Compounding and veterinary products	Alternative therapy and supply economics
Brand dependence	High for Vetoryl users	Varies by product and market

Trilostane’s commercial advantage is often perceived tolerability and controllability. Mitotane remains clinically relevant and limits the ability to raise price without increasing substitution.

What licensing deals affect trilostane?

The major commercial rights holder is Dechra in the U.S. Vetoryl franchise. Publicly disclosed information does not establish a recent, high-value licensing transaction that would materially change the economic outlook for trilostane.

Historical rights, regional distribution arrangements, manufacturing agreements, and veterinary-channel contracts may exist without public product-level disclosure. They are unlikely to change the central investment conclusion: trilostane is a mature, recurring-revenue veterinary product whose value is driven by commercial execution rather than patent duration.

What geographic coverage does trilostane have?

Trilostane is marketed for veterinary use in multiple jurisdictions, but product names, approved species, dosage strengths, and regulatory status vary. Vetoryl is associated primarily with canine use. Outside the United States, Dechra and other suppliers have marketed trilostane products under national or regional approvals.

Geographic risks include:

Different veterinary-drug approval standards.
National rules for compounding.
Parallel trade.
Local generic products.
Currency effects.
Distributor concentration.
Country-specific manufacturing and pharmacovigilance requirements.

The United States remains strategically important because of its large companion-animal pharmaceutical market and the commercial value of FDA approval. Europe and other developed veterinary markets provide diversification but can have more fragmented competition.

Key Takeaways

Trilostane is a mature veterinary endocrine drug, not an FDA-approved human medicine.
Vetoryl, marketed by Dechra, is the principal U.S. approved trilostane product for canine hyperadrenocorticism.
The core molecule has no meaningful current U.S. patent exclusivity.
Orange Book listing and human Paragraph IV litigation are not applicable.
Compounded trilostane is the principal immediate source of price pressure.
Mitotane is the main therapeutic alternative.
Product-level revenue is not publicly disclosed, particularly after Dechra became privately held.
Revenue is supported by chronic treatment, dose titration, monitoring, and veterinary brand familiarity.
Long-term growth is likely to be modest and dependent on diagnosis, penetration, pricing, and geographic expansion.
The asset has weak patent strength but durable commercial characteristics.

FAQs about trilostane market exclusivity and investment risk

Is trilostane still patent protected?

The core trilostane molecule is not protected by a meaningful current U.S. composition-of-matter patent. Any remaining protection would need to come from product, formulation, manufacturing, or jurisdiction-specific claims.

Is Vetoryl a human generic drug reference product?

No. Vetoryl is an FDA-approved animal drug. It is not listed as a human Orange Book reference product.

Can pharmacies legally compound trilostane?

Veterinary compounding is subject to applicable federal and state requirements. Compounded products do not automatically have the same approval and quality-control status as Vetoryl.

Is trilostane a biologic with biosimilar risk?

No. Trilostane is a small-molecule steroidogenesis inhibitor. Biosimilar competition is not relevant.

What is the largest financial risk for Vetoryl?

The largest risks are price competition from compounded products, approved veterinary alternatives, supply disruption, and limited growth in the diagnosed canine hyperadrenocorticism population.

References

U.S. Food and Drug Administration. (n.d.). Vetoryl (trilostane) capsules: Freedom of Information summary and prescribing information. Center for Veterinary Medicine.
U.S. Food and Drug Administration. (n.d.). Animal drugs at FDA: Green Book. https://animaldrugsatfda.fda.gov/
Dechra Pharmaceuticals PLC. (2023). Annual report and accounts 2023. Dechra Pharmaceuticals PLC.
European Medicines Agency. (n.d.). Veterinary medicinal products database. European Union.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

US Patents:	0
Tradenames:	1
Applicants:	1
NDAs:	1
Drug Master File Entries:	2
Raw Ingredient (Bulk) Api Vendors:	92
Clinical Trials:	2
DailyMed Link:	TRILOSTANE at DailyMed

TRILOSTANE - Generic Drug Details

What are the generic drug sources for trilostane and what is the scope of freedom to operate?

Summary for TRILOSTANE

Recent Clinical Trials for TRILOSTANE

Anatomical Therapeutic Chemical (ATC) Classes for TRILOSTANE

US Patents and Regulatory Information for TRILOSTANE