Company: ZOETIS

DELIVERY FORM: «feed additive»

ACTIVE INGREDIENT(S): cyromazine 2.12% (=21.2 g/kg)

CHEMICAL CLASS of the active ingredient(s): triazine, insect growth regulator


PARASITES CONTROLLED (spectrum of activity)

  • For fly control in and around: Horses, horse barns, horse stables and paddocks, horse race tracks.
  • When mixed into a horse’s ration according to the directions for use it will control certain fly species (mainly houseflies) that develop in the horse manure.


  • Begin feeding in the spring before flies begin to appear and continue feeding throughout the summer and into the fall until cold weather inhibits fly development.
  • Daily Dosage: Using 1/2 oz. scoop supplied with the product, mix one (1) scoop of Solitude IGR in the horse’s ration every day.
  • Alternate Day Dosage: Using 1/2 oz. scoop supplied with the product, mix two (2) scoops of Solitude IGR in the horse’s ration every other day.
  • Solitude IGR will provide a high degree of fly control and will give the best results when integrated with a well-managed fly control program which includes determining the degree of fly control desired, minimizing fly breeding sites, monitoring adult fly populations in and around the operation; and frequent examinations of manure for maggot activity. To maximize the effectiveness of Solitude IGR, horses must be individually fed with no group or trough feeding.

Read the product label for more specific details on dosage.


  • LD50 (acute oral) in rats: 3387 mg/kg for the a.i. cyromazine
  • LD50 (acute dermal) in rats: 3100 mg/kg for the a.i. cyromazine

Suspected poisoning? Read the article on cyromazine safety in this site.

Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)

  • Meat: Not for use in horses intended for human consumption.

WARNING !!!: Never use on humans, dogs or cats

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES

There are reports on housefly (Musca domestica) tolerance to cyromazine in several countries, but mainly in poultry or swine operations.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, it may be due to resistance and not to incorrect use, which is usually the most frequent cause of product failure.

Alternative chemical classes/active ingredients to prevent resistance of houseflies through product rotation:

These alternative products may not be available in all countries, or not available as feed additives.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?


*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: USA.
GENERIC BRANDS available? ?. This product itself contains generic cyromazine,

Click here to learn more about GENERIC vs. ORIGINAL drugs.

Click here for an overview on the most used antiparasitic feed additives and medicated feeds for livestock and horses.


SOLITUDE ® IGR is a feed-through larvicide for horses from ZOETIS that contains generic cyromazine.

Cyromazine is a so-called Insect Growth Regulator (IGR) belonging to the group of the Chitin Synthesis Inhibitors (CSI). It was introduced in the late 1970s (by CIBA-GEIGY → NOVARTIS → ELANCO). It is narrow-spectrum larvicide. It is abundantly used in sheep against blowfly strike and in poultry against houseflies and other filth flies. Usage in ruminants and horses is marginal. It is not used in pets. It is also used in agriculture.

Chitin is a component of the cuticle of insects, which is an essential part of their outer skeleton. If chitin is not properly produced, fly maggots die when they attempt the next molt. However, cyromazine does not really inhibit chitin synthesis, but interferes with its correct deposition. The consequence is the same: Fly maggots cannot complete molting and die. Other CSIs such as the benzoylphenyl ureas (BPUs, e.g. diflubenzuron, triflumuron) do actually inhibit chitin synthesis. But whereas BPUs exert this effect on almost all insects, cyromazine is quite specific for Dipterans (flies, mosquitoes, etc.) and some beetles. This makes it less harmful for the environment.

As all IGRscyromazine does not kill adult flies at all, and it does not immediately kill the fly maggots (larvae) either, i.e. it has no knockdown effect. Larvae will die at their next attempt to molt to the next developmental stage, which may take 1-4 days to occur, depending on age of the maggots at the time of treatment, humidity, temperature, etc.

Cyromazine is quite soluble in water, in contrast with many other parasiticides that are rather lipophilic, and is hardly metabolized after being ingested with the feed. In mammals it is mainly excreted through urine, not in the feces. To be effective against manure-breeding flies horse urine containing cyromazine must therefore reach the excrements, where flies deposit their eggs. This may depend on stable management practices and on horse behavior.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.