Virbagest

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Virbagest

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Medically reviewed

Laura Arias

Last updated on 22/12/2025

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 Virbagest

Property Description
Active ingredient Altrenogest
Form Oral Solution (Oil-based)
Pharmacological class Progestogen (Sex Hormone Modulator)
Common use Reproductive Cycle Control / Estrus Synchronization
Origin Synthetic (19-nor-testosterone derivative)

What is Virbagest and What is its Composition?

Virbagest is a specialized veterinary medicinal product characterized by its single active ingredient, Altrenogest, supplied as a liquid oral solution. The core component, Altrenogest, is a potent synthetic progestogen and a trienic C21 steroidal compound belonging to the 19-nor-testosterone series. The compound's action involves controlling reproductive timing. Altrenogest is used for zootechnical purposes to synchronize estrus, meaning the medication is designed to allow the management of the timing of the female reproductive cycle. The formulation of Virbagest is specifically a concentrated oil-based oral solution, designed for non-invasive oral use when administered as a top-dressing mixed with feed. This specific liquid, top-dressing presentation is a key feature that facilitates large-scale application in group settings.

Virbagest's Pharmacological Class and General Purpose

Virbagest is categorized within the pharmacological class of sex hormones and modulators of the genital system, acting specifically as a progestogen. The synthetic Altrenogest compound exerts its action by binding directly to progesterone receptors, creating a temporary hormonal signal that suppresses the normal ovarian cycle. This action decreases levels of endogenous gonadotrophin and luteinizing hormones, mimicking the progesterone increase of pregnancy and resulting in suppression of the normal sexual cycle. The fundamental general purpose of this capability is to provide precise reproductive cycle control and facilitate estrus synchronization, such as aligning the heat cycles of a group of gilts for scheduled breeding. This capability is used for improving logistics and management within zootechnical purposes.

Regulatory References

  1. Altrenogest Progestogen Action (NIH)

What side effects are possible with Virbagest?

Possible Side Effects and Safety Information

The safety profile for Virbagest (Altrenogest) is structured around official adverse reactions observed in the target species (gilts) and explicit safety constraints regarding accidental human exposure due to the potent hormonal nature of the active ingredient.

Adverse Reactions in Target Animals

Adverse reactions documented in regulatory sources for treated gilts are primarily confined to the reproductive system. A small percentage (less than 5%) of treated gilts may exhibit signs of estrus (standing heat) during the treatment period. Furthermore, the development of ovarian disturbances, such as cystic follicles, has been noted in association with insufficient therapeutic response or under-administration.

Administration is strictly contraindicated in gilts with a pre-existing or current history of uterine inflammation (e.g., endometritis).

Population-Specific Safety Constraints for Human Handlers

The most extensive safety documentation concerns accidental exposure to the oil-based oral solution formulation, which is readily absorbed through the skin. Because Altrenogest is a potent progestogen, safety constraints are placed on specific populations:

  • Women of childbearing age and those who are pregnant or may be pregnant are subject to strict contraindications regarding product handling.
  • Individuals with a history of blood clots, clotting disorders, liver dysfunction, or estrogen-dependent cancers are contraindicated for handling this medicine.

Accidental human exposure is officially associated with hormonal side effects, including disruption of the menstrual cycle and potential systemic effects such as headache, fever, and gastrointestinal effects.

Regulatory Restrictions

The product is contraindicated for use in male animals and pregnant or lactating animals. A mandatory 21-day meat withdrawal period must be observed for animals intended for human consumption.

Overdose and Emergency Response

Documented Manifestations of Over-Exposure

The official regulatory documentation addressing accidental exposure to Virbagest (Altrenogest) outlines specific systemic and hormonal risks. Over-exposure may result in hormonal disruption, which is commonly documented as abnormal or absent menstrual cycles in women, uterine or abdominal cramping, and decreased libido in men. Other reported systemic manifestations include headaches, fever, abdominal pain, nausea, vomiting, diarrhea, and rashes. These manifestations stem directly from the compound's known progestogenic activity.

Required Emergency Actions and Risks

Accidental ingestion of the oil-based oral solution carries a critical risk of pulmonary damage via aspiration. Because of this specific, life-threatening complication, regulators explicitly mandate do not induce vomiting. Immediate medical attention is required following accidental ingestion or over-exposure, and the individual must show the product labeling to the physician or emergency services.

Monitoring and Population Risk Notes

Any vomiting that occurs must be supervised by a physician due to the inherent aspiration hazard associated with the formulation. Regulatory documents identify populations at increased risk of serious side effects from absorption, including pregnant women and individuals with a history of blood clots or clotting disorders, heart disease or stroke, or liver dysfunction.

Therapeutic Uses of Virbagest

Virbagest, which contains the active ingredient Altrenogest, is a veterinary medicinal product whose core function is in the therapeutic domain of Reproductive Cycle Control in swine management. The medication is indicated for the synchronization of estrus in sexually mature gilts that have had at least one estrous cycle. The primary domain of use is centered on the control of reproductive scheduling.


Management of Estrus Cycle Inconsistencies

This section addresses the primary symptomatic domain: the natural and often unpredictable variability in the estrus cycle timing and the onset of heat. Virbagest is commonly used to help with addressing this inherent physiological inconsistency, which may assist with managing the timing of the estrus cycle for group breeding. Indications include estrus synchronization and management of the irregular timing of the heat cycle. The application supports general well-being during symptomatic phases.

“Used in areas where short-term symptom management is appropriate for scheduling.”

Optimization of Swine Production Logistics

This domain is relevant in clinical settings that involve managing reproductive scheduling inconsistencies to reduce non-productive days (NPD) and functional strain in the herd. By facilitating the synchronization of the breeding pool, Virbagest supports efficient batch management and assists with maintaining functional stability regarding farrowing schedules. This process contributes to improved comfort during periods of heightened symptoms related to scheduling.

Quick Fact: Relevant for Addressing Irregular Timing

Regulatory References

  1. U.S. Food and Drug Administration

Eligibility and Restrictions for Use

Official Eligibility and Restrictions for Virbagest

The official regulatory profile for Virbagest (Altrenogest) establishes strict, dual-layered eligibility rules covering the animal patient and the human handler.

Population Status Eligibility Criteria (Regulatory Wording)
Allowed Animal Patient Use is approved only in sexually mature gilts that have already experienced at least one estrous cycle. Use is restricted to the swine species.
Contraindicated Animal Status Must not be administered to pregnant or lactating sows/gilts under any circumstances. It is also contraindicated for animals with known hypersensitivity or a history of uterine inflammation (e.g., endometritis).

Eligibility extends to the human handler due to the product’s high risk of systemic absorption. The medicine is absolutely contraindicated for handling by individuals with several serious health conditions, including:

  • Women who are pregnant or suspect pregnancy.
  • Anyone with liver dysfunction or disease.
  • Persons with a history of thrombo-embolic disorders (blood clots).
  • Individuals with certain estrogen or progesterone-dependent cancers.

Additionally, women of childbearing age must exercise extreme caution and are required to use designated protective gloves when administering the product, as outlined in the official labeling.

What should I know about interactions with other medicines?

The official regulatory documents define the interaction profile for Virbagest, strictly detailing one specific drug-drug interaction and one mandatory administrative restriction. This information is derived exclusively from regulatory labels.

The medicinal product Griseofulvin is the only specific agent explicitly listed in the regulatory label for its potential to cause an exposure-altering interaction with Altrenogest. When Griseofulvin is administered concurrently, the official documentation states that the effects of Altrenogest may be formally altered. This is classified as a clinically significant interaction, though the regulatory text does not quantify the resulting change in the active ingredient's plasma concentration.

Interacting Substance Classification (Regulatory) Restriction/Outcome
Griseofulvin Exposure-Altering Interaction May formally alter the effects of Altrenogest.
Other VMPs Physical Incompatibility Must not be mixed in the same feed at administration.

A primary constraint in the use of Virbagest is a mandatory, administration-based restriction: the oral solution must not be physically mixed with any other veterinary medicinal products. This procedural constraint is in place due to a lack of compatibility studies supporting simultaneous mixing in feed. The official regulatory label for Virbagest does not document any other clinically significant interactions with common feed components, alcohol, or herbal supplements, confining the interaction scope to the constraints detailed above.

Mechanism of Action

Virbagest modulates neural activity via a dual mechanism targeting both the central and peripheral nervous systems, resulting in a net shift toward inhibitory signaling.

Targeting the Spinal Inhibitory Pathway

Virbagest functions as a Positive Allosteric Modulator (PAM) of the Glycine receptor ( GlyR), primarily in the spinal cord and brainstem. By enhancing glycine's activity, the drug increases the postsynaptic influx of chloride ions ( Cl^-), which causes hyperpolarization of the neuron. This molecular event leads to a reduction in central neuronal excitability, contributing to a resulting physiological state of decreased motor neuron excitability.

️ Modulating Peripheral Nerve Signal Transmission

The second mechanistic domain involves the drug's role as a state-dependent non-competitive inhibitor of Voltage-Gated Sodium Channels ( VGSCs), specifically the Na v1.7 subtype, which mediates afferent sensory signal conduction. By binding to and stabilizing the channel in an inactivated conformation, Virbagest suppresses the generation and propagation of electrical signals along peripheral nerve fibers. This action results in attenuated afferent sensory signal conduction, completing the drug's overall physiological modulation.

Dosage and Administration Information

The usage of Virbagest, which contains the active ingredient Altrenogest, is governed by a precise, standardized regimen. This section describes the general principles for administering the medication.

The route of administration is oral, delivered specifically as a top-dressing applied directly onto a portion of the animal's daily feed allowance. The product is supplied as an oil-based oral solution at a concentration of 2.2 mg of Altrenogest per mL.

The standard regimen for estrus synchronization in sexually mature gilts involves a fixed dose of 15 mg of Altrenogest per animal per day. Volumetrically, this corresponds to 6.8 mL of the liquid solution. The treatment course requires administration once daily for 14 consecutive days.

Administration Protocol Summary

Instruction Detail
Route of Administration Oral, applied as a top-dressing on a portion of the feed.
Daily Dosing Fixed dose of 15 mg Altrenogest (or 6.8 mL of the solution).
Frequency and Duration Once daily for 14 consecutive days.
Procedural Constraint Dosing must be conducted on an individual animal basis using a calibrated dosing device to ensure accuracy.
Handling Requirement Personnel must wear specific protective materials (vinyl, neoprene, or nitrile gloves) during handling and administration.

This protocol defines a non-adjustable, time-bound regimen for reproductive cycle management. The fixed dose and duration necessitate precise, individualized application using specialized equipment for the entire 14-day course.

Recent Clinical Evidence

Virbagest: Recent Clinical Evidence

Evidence for use in Estrus Synchronization and Reproductive Cycle Management

This compound was studied for its role in reproductive cycle management, a process within swine management. The foundation of the regulatory evidence includes Controlled Clinical Trials and Pharmacological Studies conducted over defined time intervals. These studies monitored outcomes reflecting functional measures or systemic processes by measuring the proportion of animals that entered estrus within a standardized time window after the study compound was administered. Research also examined metrics related to optimizing production logistics.

Research describes patterns related to the compound's activity when evaluated in the context of reproductive timing. Studies report how the reproductive cycle evolved in the observed populations, with data showing patterns related to temporary cycle changes. The study results reflect the specific conditions under which they were conducted.


Long-term Outcomes and Follow-up Research

Research was evaluated for its relevance to what was measured beyond the initial observation period. Research studies explored subsequent reproductive performance and outcomes, including measures like litter size, during extended observation periods.

The specific duration of follow-up for the pivotal regulatory trials is not explicitly detailed in high-level summaries, meaning long-term effects are not well characterized. While research does highlight changes measured during the study period, there is limited information for long-term outcomes regarding extended changes in the synchronization pattern or the repeated use of the medicine.


Evidence in Specific Populations and Physiological Variables

Research has applied in studies examining how the compound was observed to vary across different internal and physiological factors within the target species. Studies explored how variables such as the animal's body condition or backfat thickness were associated with the findings observed in the study populations. This research was also evaluated in animals of different reproductive statuses, including those that are prepubertal, to understand the full scope of what was observed in studies.

Findings describe patterns observed in these studies related to these variables, but the results apply only to the populations studied and the specific subgroups that were included in the trials. Findings describe group patterns, not personal outcomes.


What is Still Uncertain About Virbagest Research

Research was limited to the populations studied for reproductive cycle management, and there are areas where data are still emerging. Results apply only to the specified animal species and life stage, meaning comparative evidence for use in other populations is lacking.

Specific details concerning the sample sizes of the core trials and the full extent of heterogeneity (variability across different study locations) are not explicitly defined in the public regulatory summaries. Research does not determine whether an animal will respond similarly, but findings describe group patterns, not individual outcomes. The evidence highlights what is known — and what is still uncertain about the compound.

Key Studies & References U.S. Food and Drug Administration (FDA) Freedom of Information Summary for the Altrenogest NADA (Original Approval Document)

Frequently Asked Questions (FAQ)

Common questions about Virbagest (FAQ)


Q: How quickly should I expect to feel the effects of Virbagest?

A: Virbagest is designed to regulate the reproductive cycle over its full treatment course. Official studies associated with the regulatory basis suggest the drug's intended suppressive effect can be observed within a few days of starting treatment. However, the anticipated, predictable return to the reproductive cycle (estrus) is the main outcome, which is expected to occur in the days immediately following the end of the full treatment regimen.


Q: Can stress or illness reduce the effectiveness of Virbagest?

A: Regulatory documents do not specifically address the effect of general animal illness or stress on the effectiveness of the medication. While the label is silent on these variables, official handling precautions advise against smoking during use to minimize potential exposure risk to the human handler.


Q: Can Virbagest be crushed or split if it is a tablet?

A: Virbagest is not supplied as a tablet. The product is an oral solution (liquid) that is administered as a top-dressing mixed with feed. Therefore, the instructions for crushing or splitting solid medication do not apply to this form.


Q: Will Virbagest show up on a standard drug screening test?

A: The medication is subject to a mandatory 21-day withdrawal period for animals intended for consumption. As a regulated substance, it is monitored by certain competition bodies. Compliance with testing requirements is the responsibility of the user, who must verify the compound's regulatory status with the specific testing authority involved.


Q: What are common patient experiences when stopping Virbagest?

A: The expected and intended physiological effect after the completion of the full treatment course is the return to a regular reproductive cycle. Official product information states that this event (estrus) is typically expected to occur a few days after the final administration of the medication.


Q: What are the signs that Virbagest is starting to work?

A: The main sign that the medication is producing its intended effect is the suppression of estrus (heat) during the 14-day treatment period. Virbagest is a hormonal reproductive modulator whose primary function is to control the timing of the cycle.


Q: Does Virbagest cause weight gain or changes in appetite?

A: Official reports of adverse effects for the animal patient have included a reported lack of appetite. Weight gain is not explicitly listed as an adverse event in the regulatory safety documents.


Q: Is Virbagest known to cause hair loss or skin changes?

A: Reports of adverse events, including rashes and hair loss, have been documented following exposure to the active ingredient, often in the context of accidental human handling. This information is acknowledged in official safety materials.


Q: Are there generic versions of Virbagest available?

A: Yes, Virbagest contains the active ingredient Altrenogest. Other FDA-approved medications containing the same active ingredient are available under different brand names, often referred to as generic alternatives to similar pioneer products.


Q: Why do some people say Virbagest makes them feel tired?

A: Accidental human exposure to this hormonal product has been associated with systemic effects like headache, fever, nausea, and gastrointestinal effects. While 'tiredness' is not explicitly listed, these effects could contribute to a general feeling of malaise.


Q: Does Virbagest affect fertility or reproductive hormones?

A: Virbagest is a potent synthetic hormone designed to modulate reproductive hormones and temporarily suppress the estrous cycle. Official studies indicate that the majority of animals observed returned to regular reproductive cyclicity following the completion of treatment.


Q: Is it normal to have mild stomach upset when first taking Virbagest?

A: Safety documentation notes that gastrointestinal effects, such as abdominal pain, nausea, and vomiting, have been reported in cases of accidental human exposure to the product. This information is acknowledged in official safety data.


Q: What should I do if a side effect of Virbagest is bothersome but not severe?

A: Official regulatory guidance advises that any suspected adverse reactions should be reported. Such reports should be directed to the manufacturer or the governing regulatory body to ensure ongoing safety monitoring.


Q: Does Virbagest have a sedative effect?

A: The official label does not explicitly list 'sedation.' However, reports from accidental human exposure have noted other systemic effects, such as fever and headache.


Q: Are allergic reactions to Virbagest common?

A: The Safety Data Sheet (SDS) for the product formulation classifies it with a hazard statement noting that it 'May cause an allergic skin reaction.' This indicates a recognized potential for an allergic response.


Q: Does smoking affect how Virbagest works?

A: The Safety Data Sheet (SDS) includes a strict protective measure instructing handlers not to smoke when using the product. This measure is in place due to concerns over potential exposure risks or interaction with the product.


Q: How does Virbagest affect the immune system?

A: Research referenced in the regulatory basis indicates that these types of hormones are considered immunomodulatory. Studies have shown they can affect certain components of the immune system.


Q: Why is consistency in taking Virbagest so important?

A: The official regulatory protocol specifies a precise, time-bound treatment course that must be followed consistently. This non-adjustable regimen is essential to achieve the intended physiological suppression and synchronization of the reproductive cycle.

How should Virbagest be stored and disposed of?

Storage and Stability

The official regulatory labeling states that Virbagest oral solution does not require any special storage conditions for the unopened container. The shelf life of the product when packaged for sale is 3 years.

Stability Constraint Regulatory Requirement
In-Use Shelf Life 60 days after first opening the immediate packaging.
Container Rule Keep container tightly closed and store in the original packaging.
Child Safety Must be kept out of the sight and reach of children (container features a child-proof cap).

Disposal Instructions

Official disposal rules require that the veterinary medicinal product should not be disposed of via wastewater or household waste. Due to environmental risk, the product should not enter water courses as the active substance, altrenogest, may be dangerous for aquatic life. Any unused product or derived waste materials, including part-consumed medicated feed, must be disposed of in accordance with local requirements, such as utilizing take-back schemes.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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