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Brand: VETRAZIN ® Spray-on / Pour-on


FORMULATION: «spray-on/pour-on» for topical administration.

ACTIVE INGREDIENT(S)cyromazine 60 g/L (= 6%)

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 in all breeds of long wool sheep, incl. lambs.
  • Length of protection:
    • Australia up to 11 weeks
    • UK up to 10 weeks
    • New Zealand up to 6 weeks


* Can be slightly different in some countries: read the product label!

Use recommendations in Australia, based on time after shearing:

Months since shearing Dose rate (mL) Vol.per treatment band (mL) Number of bands
For the prevention of body strike
up to 6 34 17 2
7 38 18 2
8 44 22 2
9 50 25 2
10 56 28 2
lambs <15 kg 17 17 1
For the prevention of body & crutch strike
Up to 6 51 17 3
7 57 19 3
8 66 22 3
9 75 25 3
10 84 28 3
lambs <15 kg 34 17 2

  Use recommendations  in the UK, based on weight:

Weight in kg Dose rate (mL) Vol.per treatment band (mL) Number of bands**
For the prevention of body, tail & crutch strike
11-15 15 17 2
16-20 20 18 2
21-30 30 22 2
31-40 40 25 2
≥41 50 28 2
For the prevention of tail & crutch strike only
11-15 7.5 17 1
16-20 10 19 1
21-30 15 22 1
31-40 20 25 1
≥41 25 28 1

 ** The applicator gun should be set to deliver half the required dose in one squirt. One squirt should then be applied along the spine from the middle of the shoulder to the rump and a second squirt around the crutch and tail area.

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


  • LD50 (acute oral) in rats: 3387 mg/kg for the active ingredient (source: MSDS). Estimate for the formulation: >5000 mg/kg.
  • LD50 (acute dermal) in rats: 3100 mg/kg mg/kg for the active ingredient (source: MSDS). 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 & shearing (country-specific differences may apply: read the product label)

  • Meat: UK 28 days; Australia 7 days (ESI 28 days); New Zealand 7 days.
  • Milk for human consumption: Not approved in UK and Australia. New Zealand: discard milk for 35 days following treatment.
  • Shearing: Australia & New Zealand 2 months.


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 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 2008. Since then approved only for lice control.

First cases of blowfly field resistance to the chemical classes mentioned above 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.

In 2012 a first report on Lucilia cuprina cyromazine tolerance was reported (Resistance Factor = RF ~3) almost 40 years after the introduction of the first cyromazine product (VETRAZIN Liquid for dipping and jetting) in the late 1970s. In 2020 field resistance of blowfies to cyromazine has been reported for Lucilia cuprina in Australia with a RF of about 25. These blowflies have been reported to be also resistant to dicyclanil and ivermectin treatment.

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 as spray-ons/pour-ons.

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: Australia, UK, Ireland and other EU countries, New Zealand, South Africa
GENERIC BRANDS available? YES, in Australia and New Zealand.

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

For an overview on the most used antiparasitic pour-on brands click here.


VETRAZIN Spray-on/Pour-on for sheep was developed by CIBA-GEIGY (later NOVARTIS → ELANCO) in the early 1990s as a ready-to-use complement to its first and original cyromazine formulation for dipping and spraying (VETRAZIN Liquid) against blowfly strike. The spray-on and the pour-on formulations have the same composition, they are just different brands used in different countries.

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.


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.