ABSTRACT: Perhaps no area of veterinary medicine has grown as rapidly as the field of flea and tick control. Fleas have become resistant to many products and with the explosion in flea numbers, there are huge efforts aimed at controlling them. Ticks can also transmit a number of diseases, so tick control is also receiving more attention

Today’s insecticides for pets represent great advances and a wide array of different compounds has been formulated. The goal of this article is to explain the mechanism of action of some of the common active ingredients listed on the labels of various shampoos, dips, sprays, powders and ‘foggers, with special reference to their safety – or otherwise – in cats.

Common pitfalls

The old adage, ‘if a little is good, a lot is better’ approach is often taken by people trying to treat parasite infestations in their pets. It is not better and is potentially very toxic to pets, as well as humans in the household.

The same applies to mixing products. Too often in the zeal to kill fleas and ticks people will use more than one product at once – for example, a dip, followed by a shampoo, then adding a flea collar or spot-on treatment after that! All of which could result in a potentially very dangerous situation.

Shampoos sometimes work to kill the fleas on the animal, but usually don't have a lot of staying power. The dips are designed to last a while on the skin and coat of the animal, whilst collars and spot-ons are designed to last even longer. The mix of chemicals can indeed prove deadly – and not just to the fleas.

Why clients should come to you

The average client, who claims to use parasite control regularly on his or her pet, actually only applies between two and three flea treatments a year, so it is important to encourage owners to do better. The best method is through direct communication with the clients. It bonds them to your practice and ensures they continue to protect their pet with the safest and most efficacious products.

It is becoming increasingly difficult to compete with supermarkets and pet shops and so a pro-active approach from the practice works well. It gives you the opportunity to discuss the individual’s needs and advise accordingly. For example, if you notice when looking at a client’s records that an animal has not been treated recently with ecto- and endoparasiticides, flag it up, so that you can call them or give them advice when they next visit the practice.

As trained veterinary health advisors, you can select different approaches for multi¬pet households, outdoor versus indoor pets, or those on tight budgets. Often clients are paying more for pet shop treatments than they would for a tried and tested product from you that will provide treatment for a whole year.

Ectoparasite control agents

There are a number of flea control products for use on pets, including once- a-month topical products, sprays, dips, shampoos, collars, powders, oral and injectable products. With any product applied directly to the pet, it is important to inform owners that they may see some live fleas for a short time after application. In order for the fleas to die, they must come into contact with the insecticide, and absorb it.

Until all of the fleas in the home have died, you will probably still see some fleas even on a treated pet, since some immature forms may continue to develop. This is especially true if there was a big flea problem to start with. It is essential to keep following an effective flea control programme for a long enough time to get rid of all of the fleas, in all life stages.

It is important to note that, despite some pet shop products claims to prevent ticks, there are no products currently available from a pet store that can do this. The risk of tick-borne diseases can be reduced by the use of a product that kills the tick quickly before the agents can be transferred. Only deltamethrin may repel them from attaching.

Once-a-month topicals

Once-a-month topical insecticides that are applied to a small area on the animal’s back are probably the easiest product to use and generally last the longest. Some kill fleas and ticks, and others just kill fleas, so check the label carefully. Ingredients generally include permethrin, pyrethrin, or fipronil.

Since many dog products can be very harmful if used on cats, read the label carefully. Do not use products containing permethrins on cats.

It is an all too familiar sight to see a cat being presented at your practice, fitting and salivating, and with a greasy patch between the shoulder blades. The cause? Some uninformed owner has applied a dog spot-on, containing permethrin, to their cat.

Figure 1 shows a cat being bathed in cool water to remove the product and Figure 2 shows it receiving intravenous fluids and diazepam to try to control the fitting.

Figures 1 & 2: Cats that have inappropriate flea preparations administered need immediate veterinary attention. The treated area should be clipped off and bathed with copious amounts of tepid soapy water

The client purchased the product from a pet store without advice and assumed because she had used a safe, veterinary recommended product on both her cats and dogs, just at different amounts, that the same would apply across the whole range of available ectoparasiticides.


Flea and tick control sprays can come as aerosols or pump bottles. When dispensing a spray, you should advise the client not to soak the pet, yet be sure to spray all parts of the animal. Spray a small amount on a cotton ball or gloved hand to apply the product around the eyes and ears. Do not get any of these products in the eyes.

Warn clients about the salivation that may occur owing to the taste of the alcohol that some products contain and tell them to follow the veterinarian’s – as well as the manufacturer’s – directions on how often to spray, and to spray in a well ventilated area. Also mention the inflammable nature of some products.


Dips and rinses are applied to the entire animal. They generally have some residual activity. They should be applied in a well ventilated area according to the veterinary and manufacturer’s directions. It is helpful to put cotton balls in the pet’s ears and ophthalmic ointment in their eyes. Even with these precautions, be very careful not to get any of the product in the pet's ears or eyes. Dips or rinses may contain pyrethrins, permethrins or organophosphates.


Flea and tick shampoos help primarily to rid the pet of the fleas and ticks it already has, although some have residual activity. To use a flea and tick shampoo properly you must be sure to work the shampoo in over the entire body and then leave it on for at least 10 minutes before you rinse it off. Remember to protect the eyes and ears of the pet. Shampoos often contain pyrethrins.


Flea and tick collars can be effective, but must be applied properly. To achieve the right degree of snugness, you should just be able to insert two fingers between the collar and the pet’s neck. Be sure to cut off any excess portion of the collar after you have properly applied it in order to prevent that animal, or other pets, chewing on the end. Check the package for information on duration
of effectiveness, since some collars lose effectiveness when they get wet. Warn owners to watch for any irritation under the collar. If this occurs, you may need to recommend a different product.

Do not use collars containing amitraz, permethrin or organophosphates on cats.

Oral and injectable products

A product containing the insect development inhibitor, lufenuron, is available as a tablet for dogs and cats and as an injectable for cats. The tablets are given once a month; the injection is given every six months. The product does not kill the adult fleas, so if they are present, an appropriate adulticide treatment is required.

Another oral product, based on the active nitenpyram is approved for use in dogs and cats. It will kill adult fleas, but only for a period of one day or less. It is useful in situations such as boarding, grooming, and prior to surgery. Because the active ingredient is excreted from the pet’s system within 24 hours, it should be followed with a longer-lasting product that will work on both adult and immature fleas.

Flea combs

Flea combs are often overlooked as a valuable tool in removing fleas (Figure 3).

Figure 3: A cat flea, Ctenocephalides felis

Pets love the extra, hands-on attention they receive and combs are absolutely non-toxic and are the best method to use on ill, pregnant or infant pets. Be sure to choose a comb that has 32 teeth per inch.

Comb the pet and then place the fleas you comb off in detergent water, which will kill them. The disadvantage to flea combing is that it takes a considerable amount of time, and will not be effective in pets that have flea bite hypersensitivity.

The best flea control is always flea prevention.

Insect growth regulators and development inhibitors

Insect growth regulators (IGRs) and insect development inhibitors (IDIs) are relatively new components of flea and tick products. Insect growth regulators include methoprene, fenoxycarb, and pyriproxyfen. Insect growth inhibitors include lufenuron and diflubenzuron. IGRs and IDIs differ from traditional flea product ingredients in that their main activity is against the immature forms of the flea.

The IGRs mimic the juvenile growth hormone of fleas. The juvenile growth hormone is what keeps the fleas from developing into more mature forms. When the levels of juvenile growth hormone decrease, the larva form matures. The IGRs keep this development from occurring and the immature forms of the flea fail to moult and death occurs.

The IDIs inhibit the synthesis of a substance called chitin. Chitin is necessary for the formation of the hard outside skin (cuticle) of the flea. No chitin, no adult flea.

Note that the IGRs and IDIs do not kill the adult fleas, so to be most effective, they should be used along with a product that does kill the adults (adulticide). Many IGRs and IDIs are used in the environment as ingredients in foggers and sprays. They are also applied topically to cats and dogs, or given orally, or by injection.

Because IGRs and IDIs mimic insect hormones or alter a unique insect process (the making of chitin, which mammals do not make), they are extremely safe. This is a selling point we can use to encourage owners to purchase our products rather than those less specific ones available more widely.



Amanda graduated from Liverpool University in 1998 and has since worked as a veterinary surgeon in Cornwall, first in mixed practice and later in critical care and emergency work. She enjoys writing for the veterinary press and has contributed to several nursing textbooks.

Further reading

ROCK, A. (2007) Veterinary Pharmacology – A Practical Guide for the Veterinary Nurse Butterworth Hememann Elsevier

• VOL 25 • No9 • September 2010 • Veterinary Nursing Journal