Company: HARTZ

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


  • ETOFENPROX: 550 mg/ml (=55.0%)
  • METHOPRENE: 2.5 mg/mL (=0.25%)
  • PYRIPROXYFEN (=Nylar): 5.0 mg/mL (=0.5%)
  • PBO: 100 mg/kg (=10%): no direct therapeutic effect
  • MGK 264: 10 mg/kg (=1%): no direct therapeutic effect

CHEMICAL CLASS of the active ingredient(s):


PARASITES CONTROLLED* (spectrum of activity)

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


  • Dogs, small 5 to 14 lbs.  2.3 to 6.7 kg bw: 1 pipette with 0.5 mL (equivalent 119.6 - 41.0 mg/kg etofenprox, 0.5 to 0.2 mg/kg methoprene, 1.1 - 0.4 mg/kg pyriproxyfen)
  • Dogs, medium  15 to 30 lbs.  6.8 to 13.6 kg bw: 1 pipette with 1.95 mL (equivalent 157.7 - 78.9 mg/kg etofenprox, 0.7 to 0.4 mg/kg methoprene, 1.4 - 0.7 mg/kg pyriproxyfen)
  • Dogs, large 31 to 60 lbs.  14 to 27.2 kg bw: 1 pipette with 3.90 mL (equivalent 153.2 - 78.9 mg/kg etofenprox, 0.7 to 0.4 mg/kg methoprene, 1.4 - 0.7 mg/kg pyriproxyfen)
  • Dogs, very large 61 to 150 lbs.  27.6 to 68.4 kg bw: 1 pipette with 6.5 mL (equivalent 129.5 - 52.3 mg/kg etofenprox, 0.6 to 0.2 mg/kg methoprene, 1.2 - 0.5 mg/kg pyriproxyfen)

* 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. Never use on small dogs pipettes approved for large dogs. 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, and in brown dog ticks (Rhipicephalus sanguineus) in some countries (e.g. the USA, Panama, Brazil and Spain). 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, mosquitoes and brown dog ticks may be lower or shorter than expected.

This product contains two synergists (PBO and MGK 264) that have no direct effect on the parasites, but are supposed to neutralize pyrethroid resistance due to enhanced detoxifixation through mixed function oxidase (MFO) enzymes. However detoxification through MFOs is only one among several possible resistance mechanisms (e.g. other detoxifying enzymes, target site insensitivity, reduced penetration, behavioral change, etc). This means that the chance that these added synergists overcome resistance to etofenprox in fleasmosquitoes and ticks is rather modest. And it is impossible to know in advance whether they will work or not. Consequently if the product does not work, you will never know whether it is due to incorrect administration or to resistance.

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

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 brown dog ticks 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)
  • Pyriproxyfen (Nylar): GENERIC (introduced in the 1990s)
  • PBO: GENERIC (introduced in the 1940s)
  • MGK 264: GENERIC (introduced in the 1940s)

*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 dogs is a once-a-month flea+tick spot-on from HARTZ combining etofenprox (kills fleas, kills and repels ticks and mosquitoes) with methoprene and pyriproxyfen that both inhibit the development of fleas.

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. Dermacentor variabilis, Ixodes scapularis, Rhipicephalus sanguineusAmblyomma americanum, etc,) 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.

Pyriproxyfen (Nylar) is a veteran insect development inhibitor introduced in the 1980s (by SUMITOMO) scarcely used in pets and not at all in livestock. It is also used moderately in agriculture and vector control. In this product it stops development of flea eggs and larvae. It has no protective effect whatsoever against fleas, ticks, mosquitoes, and biting flies

Methoprene and pyriproxyfen have no effect on ticks or mosquitoes, only on the development of flea eggs and larvae. 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 or ticks through two or more different mechanisms of action, which is vastly assumed to help preventing or at least delaying resistance development.

The logic of combining etofenprox with an IGR is to ensure that if a few fleas survive its killing effect (what usually happens) development of their offspring is inhibited, because the eggs of the surviving fleas won't developed.

Usually only one IGR is included in many flea spot-ons. The logic of adding two with a similar mechanism of action (juvenile hormone analogues) is not evident, also because so far there are no reports on flea tolerance or resistance to these IGRs.

As previously mentioned, both synergists in the formulation (PBO and MGK 264) have neither a direct effect on fleas, ticks or mosquitoes, nor enhance the efficacy of etofenprox. The chance that they neutralize resistance to etofenprox is very modest.

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, mainly on dogs. 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. Etofenprox is less toxic and irritant than other synthetic pyrethroids, but adverse drug reactions are not surprising when administered at such high doses as in this case.

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, 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 dog spot-on etofenprox is delivered at a concentration of 55.0%, which results in a dose rate of up to up to ~158 mg/kg,  about 30 to >100 times more than on cattle. It is not surprising that not all dogs tolerate such a dose, particularly small breeds, puppies and weaker animals (sick, stressed, old). 

A comparable situation occurs with amitraz for dogs (and cats, to which amitraz is also toxic). There are no amitraz ready-to-use pour-ons for cattle, because cattle just don't tolerate it at high concentrations. Instead there are topical amitraz sprays or dips that are applied to cattle at concentrations of ~0.025% (250 ppm = mg/L), which results in a dose of 3-5 mg/kg body weight. Even at this dose cattle may not tolerate amitraz and show undesirable side effects (sedation, depression, etc). Spot-ons for dogs may contain up to 10% amitraz and can result in doses of up to 45 mg/kg body weight! Chihuahuas and puppies are particularly at risk of amitraz side effects.

It is also not surprising that such products erroneously administered to cats can be deadly.

In fact, 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.

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


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.