Brand: NEPOREX ®  2 SG

Company: ELANCO

DELIVERY FORM: soluble granules for environmental treatment

ACTIVE INGREDIENT(S): cyromazine 2% (= 20 g/kg)

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


PARASITES CONTROLLED (spectrum of activity)


  • Dry scattering
    • USA: 1 lb / 200 Sq. Ft.
    • Australia & UK: 250 g product /10 L water for 10 m2
  • Spraying
    • USA: 1 lb / 200 Sq. Ft.
    • Australia & UK: 250 g product / 10 L water for 10 m2
  • Treatment Interval: The recommended treatment interval depends on management and housing systems as well as on climatic conditions. It can vary from 21 days up to several months.
  • Read the product label for more specific recommendations & restrictions in each country


  • 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

Withholding periods (=withdrawal times): approved only for use off-animals

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

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 numerous reports on tolerant or even resistant houseflies to cyromazine in many countries (USA, UK, Denmark, Argentina, Brazil, etc.). This is not surprising more than 40 years after its introduction in the early 1980s.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, there is a real risk that it is 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 for spraying or scattering over fly breeing sites

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, Australia, UK and many other countries.
GENERIC BRANDS available? Yes, but not everywhere.

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

Click here for an overview on the most used antiparasitic BRANDS with concentrates for dipping, spraying, or jetting.


NEPOREX 2G is one of the original cyromazine formulations introduced in the early 1980s (by CIBA-GEIGY, now ELANCO) for off-animal treatment of fly breeding sites (manure, organic garbage, etc.) in livestock operations.

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 so far 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.


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.