Company: NEXAN

FORMULATION: concentrate for topical administration to sheep by «dipping», «spraying» or «jetting»

ACTIVE INGREDIENT(S): Cyromazine 500 g/L (= 50%)

CHEMICAL CLASS of the active ingredient(s): Insect growth regulator (= IGR, triazine)


PARASITES CONTROLLED * (spectrum of activity)

* Country-specific differences may apply: read the product label.

  • For the prevention of blowfly strike (incl. Lucilia cuprina) in sheep for up to 12 weeks


* Country-specific differences may apply: read the product label.

For long term protection (up to 12 weeks)

  • Mix 2 litres of product with 1000 litres of water (1 in 500 dilution; equivalent to 1000 parts per million = ppm = mg/L in the wash) and apply by showering, plunge dipping or jetting. Top up at the same rate. Because ths is a non-stripping dip, no reinforcemente is required.

For medium term protection (up to 6 weeks)

  • Mix 1 litre of product with 1000 litres of water (1 in 1000 dilution; equivalent to 500 parts per million = ppm = mg/L in the wash) and apply by showering, plunge dipping or jetting. Top up at the same rate. DO NOT use this rate for hand jetting and through spray races. Because ths is a non-stripping dip, no reinforcemente is required.

Read the product label for further details on dosing and administration.


  • LD50 (acute oral) in rats: 3387 mg/kg for the active ingredient. Estimate for the formulation: >5000 mg/kg.
  • LD50 (acute dermal) in rats: >3100 mg/kg mg/kg for the active ingredient. Estimate for the formulation: >5000 mg/kg.
  • Estimated hazard class according to the WHO classification of pesticides for cyromazine: U, unlikely to present acute hazard

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

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

  • Meat: New Zealand: 7 days
  • Milk for human consumption: New Zealand: Milk intended for sale for human consumption must be discarded during treatment and for not less than 35 days following the last treatment.
  • Wool: New Zealand: 2 months.

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? LOW, mainly in Australia.

Cyromazine is a particular case regarding resistance development. Blowflies developed resistance to most chemical classes and active ingredients that were successively used for their control in Australia (and to a large extent in New Zealand too):
  • Organochlorines (e.g. DDT, dieldrin): introduced in 1946 in Australia, field resistance detected in 1957. Withdrawn for safety reasons in the 1970s.
  • Organophosphates (e.g. diazinon, malathion): introduced in 1957 in Australia, field resistance detected in 1965. Withdrawn for safety reasons in Australia in the mid 2000s.
  • Benzoylphenyl ureas (e.g. diflubenzuron): introduced in 1993 in Australia, field resistance detected in 2001. Claim for blowfly strike prevention removed in Australia in 2008. Since then approved only for lice control.

First cases of blowfly field resistance to the mentioned chemical classes appeared usually about 10 years after product introduction. Other chemical classes such as synthetic pyrethroids (e.g. cypermethrin) and macrocyclic lactones (e.g. ivermectin) have been used only marginally for blowfly strike prevention during these years, i.e. it can be assumed that the selection pressure on blowflies exerted by chemicals of these two classes has been rather low.

It is now >35 years since the introduction of the first cyromazine product (VETRAZIN Liquid for dipping and jetting) in the late 1970s, and so far only one case of light tolerance in the field (Nimmitabel) has been reported in 2011 for Lucilia cuprina in Australia. However, even in the affected properties the product still accomplished its label claims. Tolerant flies exhibited a Resistance Factor (RF) of about 3, meaning that a three-fold concentration of cyromazine was required to kill the tolerant maggots when compared with the susceptible ones. RFs for organochlorines, organophosphates and/or benzoylphenyl ureas can reach more than 100, which means that more than a hundred-fold concentration of these compounds is required to kill resistant flies when compared with susceptible flies.

The reasons for this unexpected behavior of cyromazine regarding resistance are not completely elucidated. It may be related to the fact that the organochlorines, organophosphates and benzoylphenyl ureas were mostly used twice a year (once against blowfly strike prevention, once against lice), whereas cyromazine is usually used only once a year, which results in a lower selection pressure. It has also been also proposed that the gene mutations that confer resistance to cyromazine are not completely dominant, and that the cyromazine-tolerant flies have little biological advantage over the susceptible ones. These factors together make it difficult for the cyromazine-tolerant flies to multiply and become predominant in the fly population.

To our knowledge no reports on resistance or tolerance of blowflies (Lucilia cuprina, Lucilia sericata) to cyromazine have been reported in New Zealand, UK (and other EU-countries) or South Africa, regions where cyromazine has been also vastly used against blowfly strike for decades.

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

These alternative products may not be available in all countries, or may not be available for dipping, jetting or dressing.

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: New Zealand
GENERIC BRANDS available? YES, several ones. This product itself is a generic brand.

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.


CYROMAX LIQUID for sheep is a generic version of VETRAZIN Liquid introduced in the late 1970s by CIBA-GEIGY (later NOVARTIS, now ELANCO). 

Cyromazine is a so-called Insect Growth Regulators (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, moderately in poultry, marginally in horses, but not in other livestock or pets. It is also moderately used in agricultural pesticides.

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 an almost all insects, cyromazine is quite specific for Dipterans (flies, mosquitoes, etc.) and some beetles. This makes it much less harmful for the environment, but also ineffective against other sheep pests such as lice. Most IGRs have no lethal effect on adult insects.

As all IGRscyromazine does not immediately kill the fly maggots (larvae), 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. For this reason, cyromazine and other IGRs are usually not used for curing established strikes, but for preventing their development by killing the very small first-stage larvae that hatch out of the eggs deposited by the adult flies on the wool.

Cyromazine is quite soluble in water, in contrast with many other parasiticides that are rather lipophilic. This means that heavy rains may significantly shorten the length of protection of this and other cyromazine-based products.

Besides concentrates for «dipping» and «jetting»cyromazine for blowfly strike prevention is also available in the form of ready-to-use spray-on/pour-on formulations.


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.