Vetoryl

Trilostane

Treatment option:

Medically reviewed

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Vetoryl

Quick Facts: Vetoryl (Trilostane)

Property	Description
Active ingredient	Trilostane
Form	Hard gelatin capsule (oral preparation)
Pharmacological class	Adrenocortical Suppressant / Enzyme Inhibitor
Common use	Management of Canine Hyperadrenocorticism (Cushing's Syndrome)
Origin	Synthetic steroid analogue

What Type of Medicine is Vetoryl (Trilostane)?

Vetoryl is a specialized, synthetic prescription veterinary medication for use exclusively in dogs, manufactured by Dechra Pharmaceuticals. Its active ingredient is Trilostane, which is formally classified as an Adrenocortical Suppressant. The drug is an oral preparation and is supplied as a single-ingredient product in a hard gelatin capsule. Vetoryl holds a unique position as an approved pharmaceutical specifically indicated for the medical management of both pituitary-dependent and adrenal-dependent Hyperadrenocorticism in dogs. This authorization provides veterinarians with a clinically recognized treatment pathway for this canine endocrine disorder.

Composition and General Purpose of Trilostane

Trilostane is a synthetic steroid analogue. Its mechanism is characterized by the reversible inhibition of the enzyme 3beta-hydroxysteroid dehydrogenase (3beta-HSD). This enzyme is pivotal in the adrenal glands, as it is required for the biosynthesis of corticosteroids, including cortisol. By targeting this enzymatic step, Trilostane works to reduce the overproduction of cortisol. Trilostane is utilized for the long-term management of Canine Hyperadrenocorticism (Cushing’s Syndrome). The general therapeutic purpose is the stabilization of the dog's hormonal environment by addressing the underlying adrenal imbalance, thereby mitigating the systemic consequences associated with chronic, elevated cortisol levels.

Regulatory References

What side effects are possible with Vetoryl?

Possible side effects and safety information

The safety profile of Vetoryl (Trilostane) is based on adverse reactions and constraints documented by governmental regulatory authorities, defining the scope of observed risks associated with the medicine.

Adverse Reaction Scope

The most common adverse reactions, as classified in official product information, primarily involve gastrointestinal and nervous system disturbances.

Classification (EMA SmPC)	Examples of Officially Listed Reactions
Common (up to 1 in 10)	Lethargy, Vomiting, Diarrhoea, Weakness, Anorexia
Uncommon (up to 1 in 100)	Collapse, Tremors

Serious Adverse Reactions and Systemic Concerns

The most clinically significant safety concern documented in regulatory sources is the risk of Adrenocortical Insufficiency (Hypoadrenocorticism), which may be severe or fatal and can occur at any time during treatment. Other serious reactions include collapse and necrosis of the adrenal cortex. Adverse effects are typically grouped into System-Organ Classes, with Endocrine System Disorders being a central focus due to the medicine's mechanism.

Population-Specific Safety Constraints

Official labels impose explicit limitations on use for specific populations. Vetoryl is contraindicated for use in pregnant, lactating, or breeding animals due to anti-progestational activity. It is also contraindicated in animals with known primary hepatic disease and in those with known hypersensitivity to the substance. Caution is advised for animals with pre-existing renal dysfunction due to an associated increased risk of renal failure. Co-administration with potassium-sparing diuretics should be avoided due to the potential for hyperkalaemia.

Regulatory Summary

The official safety information structures the risk profile around the need to monitor for signs of potential adrenocortical insufficiency, distinguishing between frequent, non-serious gastrointestinal events and rare, but life-threatening, endocrine consequences. These regulatory statements establish the mandatory safety boundaries for the medicine's use.

Overdose and Emergency Response

Vetoryl Overdose and When to Seek Help

Overdosage of Vetoryl (Trilostane) may lead to clinical manifestations associated with hypoadrenocorticism, reflecting the over-suppression of the adrenal glands. Documented signs of this over-suppression include pronounced lethargy, anorexia, persistent vomiting and diarrhea, and eventual collapse or severe weakness. Physiological findings may reveal significant electrolyte imbalances and hypocortisolemia.

Emergency Actions and Severe Outcomes

Regulatory documents state that an overdose may escalate to a severe Hypoadrenocortical Crisis and lead to tissue damage, specifically adrenal necrosis, documented as a potential life-threatening outcome. If signs of over-suppression are observed, therapy must be stopped immediately and emergency attention must be sought. Accidental human ingestion of the capsules similarly requires immediate medical advice. Due to potential hormonal effects, women who are pregnant or intending to become pregnant must avoid handling the drug.

Management relies entirely on supportive and symptomatic treatment because no specific antidote is known for Trilostane. Officially described supportive measures include the administration of corticosteroids, fluid therapy, and the correction of electrolyte imbalances. For acute overdosage, procedures such as the induction of emesis or the use of activated charcoal may be considered.

Therapeutic Uses of Vetoryl

What Vetoryl Treats: Main Uses and Benefits

Vetoryl is commonly used for managing hyperadrenocorticism (Cushing's disease) in dogs, addressing conditions characterized by periods of heightened symptoms associated with systemic imbalance. This medication is applied in clinical settings where supportive symptom management is appropriate. It is relevant in conditions involving recurrent or episodic manifestations of the syndrome.

This medication plays a role in managing symptoms that interfere with daily functioning, including excessive thirst, frequent urination, and persistent panting. It is commonly used across therapeutic domains where additional symptomatic support is needed. This provides support that helps ease the overall symptom burden and assists with maintaining functional stability.

Vetoryl also helps address symptoms that create noticeable physiological strain, such as muscle weakness and atrophy. It is relevant for easing skin and coat abnormalities like hair loss and thin skin. By managing these symptom clusters, this medication supports general well-being during symptomatic phases and contributes to improved day-to-day comfort.

Quick Fact: Supports Management of Excessive Urination and Thirst

Regulatory References

European Commission Union Register

Eligibility and Restrictions for Use

Eligibility Map: Who can and cannot use Vetoryl — Official Regulatory Information

The eligibility profile for Vetoryl (Trilostane) is strictly defined by government regulatory documents for use in dogs with Pituitary-dependent or Adrenal-dependent Hyperadrenocorticism.

Eligibility Scope

Classification	Population/Condition
Populations for whom use is contraindicated	Dogs with known Hypersensitivity to trilostane.
	Dogs with Primary Hepatic Disease or Renal Insufficiency.
Pregnancy and lactation eligibility status	Contraindicated in pregnant and lactating dogs/bitches.
Age-related eligibility rules	Contraindicated for dogs weighing less than 2.3 kg (varies by regional label).
Eligibility-related restrictions	Not recommended for animals intended for breeding (use not established).
Condition-specific eligibility rules	Requires extreme caution in dogs with pre-existing anaemia or concurrent Diabetes Mellitus, with mandatory monitoring required.

Eligibility Classifications (High-Level)

Classification	Statements as Defined in Official Documents
Eligibility severity classification	Contraindicated (Absolute Non-Eligibility), Extreme Caution (Conditional Use).
Regulatory basis	Rules defined by FDA DailyMed and European authorities.

Connection to the overall eligibility profile

The official regulatory profile strictly defines who can and cannot use Vetoryl based on mandatory exclusionary criteria related to the patient's existing organ function and reproductive status. Eligibility is conditional for dogs with specific pre-existing comorbidities, requiring mandated caution and monitoring to manage risks within the approved patient population.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Vetoryl (Trilostane) has officially documented interaction patterns that are classified based on pharmacodynamic effects and administration requirements, as detailed in regulatory documents.

Drug-Drug Interaction Restrictions

Co-administration of certain medicinal products is either restricted or prohibited due to the risk of additive effects on the body. The use of potassium-sparing diuretics (such as Spironolactone) is officially discouraged because both drugs inhibit aldosterone, significantly increasing the likelihood of hyperkalemia.

Concomitant use with Angiotensin Converting Enzyme (ACE) Inhibitors must be managed with caution. Both drug classes have additive aldosterone-lowering effects that may compromise the ability to maintain normal blood volume, renal function, and electrolyte levels. This combination carries specific warnings in regulatory labeling.

Administration and Timing Constraints

A key documented drug-food interaction affects the product's systemic exposure: Vetoryl's absorption is enhanced when it is administered with food. In the context of previous treatments, regulatory text specifies a mandatory waiting period: an interval of at least one month should elapse between the cessation of Mitotane therapy and the introduction of Trilostane.

Population-Specific Cautions

Trilostane is officially contraindicated in patients with pre-existing primary hepatic disease or renal insufficiency. This restriction addresses the critical role of these organs in drug clearance and elimination, which is necessary to mitigate potential toxicity and interaction-related risks.

Mechanism of Action

Targeted Inhibition of the 3beta-HSD Enzyme

Trilostane exerts its core molecular action through competitive and reversible inhibition of the adrenal enzyme 3beta-hydroxysteroid dehydrogenase / Delta^5-4 isomerase (3beta-HSD). This enzyme is crucial for synthesizing all corticosteroids. By binding to its active site within the adrenal cortex, trilostane transiently suppresses this required biosynthetic step.

Modulating the Cortisol Biosynthesis Cascade

Blocking 3beta-HSD disrupts the cortisol biosynthesis cascade, resulting in a systematic reduction in the circulating levels of cortisol, the primary glucocorticoid. The physiological consequence of this targeted suppression is the mitigation of systemic signaling driven by elevated glucocorticoids, supporting the regulation of adrenal function.

Reversible Action and Physiological Constraints

The mechanism is defined by its reversible nature; enzyme activity rapidly returns upon the clearance of trilostane. This characteristic governs the duration of effective physiological suppression, necessitating consistent molecular presence to influence the duration of adrenal suppression.

Dosage and Administration Information

How to Use Vetoryl (Trilostane)

The administration of Vetoryl follows a precise, standardized protocol focusing on the route, initial dosing, and long-term adjustment pattern. The medication is an oral preparation supplied in hard gelatin capsules, available in multiple strengths, including 5 mg, 10 mg, 30 mg, 60 mg, and 120 mg.

Administration Guidelines

Instruction	Detail
Route of Administration:	Exclusively the oral route.
Dosing Schedule (Initial):	Starting dose is typically 2.2-6.7 mg/kg (1.0-3.0 mg/lb) once daily.
Timing in Relation to Meals:	The capsule must be administered with food (i.e., with a meal or a small amount of food) to facilitate appropriate absorption.
Preparation Requirements:	Capsules must be administered whole and must not be opened or split.
Frequency Pattern:	Initially once daily, though the total dose may be divided and administered twice daily if clinical control does not last for 24 hours.

Usage Protocol and Course Duration

Vetoryl is used in a long-term treatment pattern that is non-cyclical. The course involves subsequent re-evaluation and adjustment, with monitoring occurring at specific intervals such as 10–14 days after initiation and every 3 to 4 months thereafter. This usage protocol governs the long-term administration. Procedural constraints include that the medication is not intended for dogs weighing less than 2.3 kg (5 lb) and handlers should wash their hands thoroughly after administration. This structure aligns the use of the medicine with a standardized approach.

Recent Clinical Evidence

Research evidence / Overview of studies for Vetoryl

The research landscape primarily focuses on studies that evaluated outcomes related to the use of this medicine for dogs with naturally occurring Hyperadrenocorticism, commonly known as Cushing's Syndrome. These studies explore its application for both recognized forms of the condition, tracking patterns observed in various symptoms and specific internal measurements during the study period.

Evidence for use in Pituitary-Dependent Hyperadrenocorticism (PDH)

This section will summarize the structure of the clinical research for the most common form of the syndrome, outlining the primary study designs (e.g., field studies) and the specific clinical and biochemical outcomes (e.g., changes in panting, thirst, and cortisol levels) that were evaluated in client-owned dogs.

The scientific evidence base for the PDH form of Hyperadrenocorticism includes multi-center field studies—which are often used for regulatory authorizations—alongside subsequent prospective clinical trials, with additional context provided by retrospective case series. Researchers used these studies to explore how symptoms change over time in client-owned adult and older dogs diagnosed with PDH.

Findings describe patterns observed in the studies related to measurable shifts in both the owner-reported clinical signs and the objective biochemical test results during the measured follow-up. The evidence highlights that, in these studies, the reported reaching of a defined point of control for clinical signs involved observation periods spanning several weeks. Studies also reported findings related to patient longevity in the observed populations.

Evidence for use in Adrenal-Dependent Hyperadrenocorticism (ADH)

This part will describe the research evidence specifically available for the less common ADH form, detailing the types of studies that exist for this population and how the evaluated outcomes track stabilization of the condition.

For the Adrenal-Dependent form (ADH), the research evidence is drawn from data submitted for regulatory authorization and subsequent scientific publications. This research examined populations of dogs whose condition was attributed to adrenocortical tumors. The findings described patterns where cortisol concentrations monitored were consistently reduced, and associated clinical signs followed improvement patterns.

However, due to the lower frequency of naturally occurring ADH compared to PDH, the existing evidence is limited by smaller total sample sizes. This means that sufficient data to characterize the response across a broad population with this sub-type remains limited.

Key Studies & References

Freedom of Information Summary - NADA 141-291 VETORYL (Trilostane) Capsules for Dogs (Original Approval)

Frequently Asked Questions (FAQ)

Common questions about Vetoryl (FAQ)

Q: What is Vetoryl used for?

Vetoryl (trilostane) is indicated for the treatment of pituitary-dependent hyperadrenocorticism in dogs, which is also commonly referred to as Cushing's syndrome. According to the official product information, it is used to manage the symptoms related to the overproduction of the hormone cortisol by the adrenal glands.

Q: How does Vetoryl work?

Vetoryl works by decreasing the amount of cortisol that the adrenal glands produce. Regulatory documents state that the active ingredient, trilostane, specifically blocks an enzyme that is necessary for cortisol synthesis. This action is intended to reduce the clinical signs of hyperadrenocorticism.

Q: Are there any contraindications for Vetoryl?

Official information indicates that Vetoryl should not be given to dogs with primary hepatic disease or renal insufficiency. It is also contraindicated for use in pregnant or lactating animals, or in breeding males. A veterinarian should assess if these conditions are present before treatment begins, as noted in the product information.

Q: What is primary hepatic disease and why is it a concern with Vetoryl?

Primary hepatic disease refers to a severe disease of the liver itself. According to regulatory documents, the drug is contraindicated in this state because the liver is essential for processing and eliminating many medicines, including trilostane. Impaired liver function could potentially affect the safety of the medication.

Q: What is renal insufficiency and why is it a contraindication for Vetoryl?

Renal insufficiency means the kidneys are not functioning properly. Studies and official information indicate that Vetoryl should not be used in dogs with this condition because kidney health is important for the overall drug metabolism and excretion process. The official documentation advises that a check for kidney impairment is typically performed by a veterinarian before treatment is initiated.

How should Vetoryl be stored and disposed of?

The storage and disposal of Vetoryl (Trilostane) must strictly follow the official instructions documented in regulatory labeling to maintain product stability and ensure safety.

Storage Conditions: The capsules must be stored in their original package to protect them from light and should not be stored above 25 C. The shelf life is 3 years when stored correctly.
Handling Precautions: Do not divide or open the capsules. Women who are pregnant or are intending to become pregnant should avoid handling the capsules. Always wash hands with soap and water after use.
Safety & Access: The medicine must be kept out of the sight and reach of children and animals.
Disposal Rules: Unused or expired capsules must not be disposed of via wastewater or household waste. Disposal must be completed in accordance with local requirements for medicinal waste.