Company: HARTZ

FORMULATION: «spot-on» solution for topical administration on the back of the animals (also called pipettes, squeeze-ons, drop-ons, etc.)


CHEMICAL CLASS of the active ingredient(s):


PARASITES CONTROLLED* (spectrum of activity)

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


  • Cats 5 lbs. 2.3 kg bw, 1 pipette with 1.8 mL (equivalent to ≤313.0 mg/kg etofenprox + ≤28.2 mg/kg methoprene)

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


  • LD50 (acute oral) in rats: >5000 mg/kg (according to study by HARTZ)
  • LD50 (acute dermal) in rats: >5000 mg/kg (according to study by HARTZ)
  • Estimated Hazard class calculated according to the WHO: U unlikely to present acute hazard (based on the LD50, learn more)

Suspected poisoning? Read the articles on etofenprox safety and methoprene safety in this site.
WARNING !!!: Never use on cats pipettes approved only for dogs or vice-versa. Learn more about spot-ons and their safety.

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


Risk of resistance? YES, significant for:

Resistance to pyrethroids (including etofenprox) is common in fleas and mosquitoes worldwide. Mosquito resistance is mostly due to large scale spraying of pyrethroids for vector control or pest control in agriculture. As a consequence protection provided by this product against fleas and mosquitoes may be lower or shorter than expected.

So far there are no reports on resistance of fleas to methoprene.

Alternatives to prevent resistance through product rotation:

*F = effective against fleas; T = effective against ticks.

These alternative products may not be available in all countries, or may be not available as spot-ons.

Resistance of fleas and mosquitoes to carbamates, organophosphates and pyrethroids is not uncommon in several countries, including the USA.

Learn more about resistance and how it develops.


Are the active ingredients ORIGINAL* or GENERICS**?

  • Etofenprox: GENERIC (introduced in the 1980s)
  • Methoprene: GENERIC (introduced in the 1970s)

*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 product is marketed (maybe under another TM): USA
GENERIC BRANDS available? YES, perhaps not with the same composition

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


ULTRAGUARD PRO for cats is a once-a-month flea+tick spot-on from HARTZ combining etofenprox (kills fleas, kills and repels ticks and mosquitoes) with methoprene that inhibits the development of fleas. The active ingredients are the same as in ULTRAGUARD PLUS for cats, just with another applicator.

Administered about every 4 weeks controls established flea infestations and prevents flea populations to develop in the pets environment, but only if all the dogs and cats in the same household are treated against fleas. It also kills/repels several tick species (e.g. Ixodes scapularis) and mosquitoes.

Etofenprox is a veteran broad-spectrum insecticide and acaricide pyrethroid introduced in the 1980s (by MITSUI). It is abundantly used in agriculture and against household pests. It is effective against fleas, ticks and mosquitoes. However, resistance of fleas and mosquitoes to pyrethroids is not uncommon, in the USA and elsewhere. This means that protection against these parasites may be lower or shorter than expected.

Methoprene (also called (S)-methoprene) is a veteran insect development inhibitor introduced in the 1970s (by ZOECON) used moderately in pets and agriculture. It has no effect whatsoever on ticks, only on fleas. The logic of adding an IGR is to ensure that if a few fleas survive the killing effect of etofenprox (what usually happens), development of their offspring is inhibited because the eggs of the surviving fleas will not develop.

The combination of more than one active ingredient of different chemical classes makes also sense regarding resistance prevention, because it means attacking fleas through two or more different mechanisms of action, which is vastly assumed to help preventing or at least delaying resistance development.

Topical products (mainly spot-ons and insecticide-impregnated collars) have some advantages over systemic products (mainly tablets for oral administration and injectables):

  • Most topical products kill or sterilize the parasites before they bite and suck blood on the pet, whereas systemic products kill or sterilize the parasites only after their blood meal.
  • Topical products cannot be vomited.
  • Spot-ons and collars are very convenient to administer.
  • There is a larger choice of topical products.

But topical products have also some disadvantages:

  • Topical products contaminate the pet's hair coat and it is advisable for children and also adults to avoid contact with the pet for several days after treatment.
  • Topical products may not control parasites in some parts of the pet's body (e.g. the ears, below the tail, between the legs, etc.), whereas systemic products reach the blood-sucking parasites through the blood wherever they are.
  • Efficacy of topical products may be reduced or shortened through exposure to dirt, sun, shampooing, washing, rain, baths, etc., whereas efficacy of systemic products is independent from these factors.

This product is one of many examples of a questionable practice regarding the use of pyrethroids at very high concentrations on pets. Photostable pyrethroids (including permethrin, cypermethrin, deltamethrin, cyphenothrin, phenothrin, etc.) can have a dose-dependent irritant effect on mammals. Most of them are toxic to cats at the therapeutic dose used on dogs.

Pyrethroid-related irritation is a well-known problem in livestock. Ready-to-use pour-ons are frequently used on cattle, comparable to ready-to-use spot-ons por dogs or cats, but usually at a concentration of 1%-5% active ingredient and at a much lower dose of 1-5 mg/kg. Even at this dose some cattle show signs of irritation, particularly dairy cows and calves. In this particular cat spot-on etofenprox is delivered at a concentration of 40.0%, which results in a dose rate of up to up to ~313 mg/kg,  about 50 to 300 times more than on cattle. It is not surprising that not all cats tolerate such a dose, particularly small breeds and weaker animals (sick, stressed, old). 

In fact, the use of a synthetic pyrethroid in cats at such a concentration (40%) is both surprising and unusual. Etofenprox is less toxic to cats than other synthetic pyrethroids, but as other pyrethroids it is only very slowly eliminated in the cat's organism, which enhaces it's toxicity.

Serious problems with adverse reactions after use of certain spot-ons have been reported in the USA, especially on cats and small dogs. According to an EPA report from 2010, most problems occurred with spot-ons containing permethrin, phenothrincyphenothrin (all are synthetic pyrethroids) and amitraz, not approved for use on cats but erroneously used on them. There have been also numerous overdosing cases of small dogs, apparently because some users buy large vials for large dogs but use them several times in smaller dogs to save money. It seems also that small dogs are more sensitive than large ones and don't tolerate the treatment as well as large ones. It also seems that some insufficiently investigated inert ingredients (e.g. solvents) in the formulations are not as harmless as they were supposed to be.

Deeper information on the misuse of synthetic pyrethroids in dogs and pets can be found in: Anadón et al. 2009. Use and abuse of pyrethrins and synthetic pyrethroids in veterinary medicine. The Veterinary Journal, 182, 7-20.

My personal opinion is that the fierce competition for market share in this largest and most profitable veterinary market has pushed some companies to take too many risks in order to launch products that are "new" or at least "different" to those of their competitors. In fact it has become very difficult to be "new", really "superior" or simply "different" in a market driven mainly by generic active ingredients during the last decade. Once one company has taken the risk, others will follow and launch their "me-too" brand, to be sure they don't miss an opportunity. With so many alternative products available, I would rather use on cats one that has no pyrethroids.

For an overview and a list of the most popular pet antiparasitics for flea, tick, lice and/or mite control click here.


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