Company: HARTZ

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




PARASITES CONTROLLED* (spectrum of activity)

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


  • Cats ≥ 12 weeks of age,  5 lbs. 2.3 kg bw, 1 pipette with 1 mL (equivalent to ≤11.3 mg/kg methoprene)

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


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

Suspected poisoning? Read the article on methoprene 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, low for: fleas, mainly the cat flea, Ctenocephalides felis

Resistance of leas to methoprene has not been reported. However, fleas have developed resistance to several other insecticides (e.g. carbamates, organophosphates and pyrethroids) and are certainly capable of becoming resistant to methoprene as well. Experience shows that prolonged and uninterrupted use of any insecticide on fleas (including methoprene) bears the risk of resistance development.

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.

Learn more about resistance and how it develops.


Are the active ingredients ORIGINAL* or GENERICS**?

  • 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 OneSpot for cats is a once-a-month flea spot-on from HARTZ with methoprene that inhibits the development of fleas.

Administered about every 4 weeks it blocks the development of flea eggs which prevents flea populations developing in the pets environment, but only if all the dogs and cats in the same household are treated against fleas.

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.

This product does not kill adult fleas. If used on cats already infested with adult fleas, the fleas on the cat will continue biting the pet and sucking blood. And those fleas hatching from the pupae in the environment will infect the cats and do the same. Several weeks or months can be required to significantly reduce the flea population in the pets environment. The concomitant use of a flea adulticide may be advisable.

Best results are obtained when administered preventatively starting before the onset of the flea season, when the flea population the pet's environment is still small.

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.

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.