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Ectoparasiticidal Agents
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Ectoparasiticidal Agents
When treating patients with ectoparasites, environment and contact animals have to be considered as well. Environmental contamination is significant with fleas and chiggers (Trombicula, Neotrombicula, Walchia) and possibly with Cheyletiella. Contact animals must be treated for all ectoparasites except Demodex and chiggers, but, if dogs are affected with scabies, cats may not have to be treated and vice versa (Table 3-7).
Table 3-7 Selected Ectoparasiticidal Agents in Small Animal Dermatology | ||||
Formulation | Comments | Indications | Side Effects | Dog dose (D) Cat dose (C) |
Ivermectin | ||||
10 mg/kg bovine injectable solution (often given orally to small animals), 10 mg/ml equine oral solution | Idiosyncratic toxicities most common in Collies and Old English Sheepdogs, but also possible in other breeds. Gradual dose increase from 50 µg/kg on day 1 to 100 µg on day 2, 150 µg on day 3, 200 mg on day 4 and 300 mg on day 5 to identify sensitive patients before severe adverse effects occur. | Heartworm prevention. Oral and subcutaneous administration: Canine and feline scabies,Otodectes cynotisinfestations, demodicosis, cheyletiellosis, lice Topical administration: Canine scabies | Lethargy, ataxia, tremors, mydriasis, coma, respiratory arrest | Heartworm prevention at 6 µg/kg monthly. Oral and subcutaneous administration (with gradual increase from 50 to 300 µg within 4 days): 300 µg/kg daily for demodicosis until 8 weeks after the first negative skin scraping, four administrations 1 week apart for all other ectoparasites. (D, C) Topical administration: Ivermectin pour-on for cattle administered at 500 mg/kg (0.1 ml/kg) applied along the dorsal midline twice 2 weeks apart was reported to be effective for canine scabies. |
Milbemycinoxime | ||||
2.3 mg, 5.75 mg, 11.5 mg and 23 mg tablets | Fairly costly | Heartworm prevention, scabies, demodicosis | Very safe drug | Heartworm prevention: 1 mg/kg monthly. Scabies: 2 mg/kg twice weekly for 4 weeks. Demodicosis: 2 mg/kg daily until 8 weeks after the first negative skin scraping for demodicosis. (D, C) |
Lufenuron | ||||
45 mg, 90 mg, 204.9 mg, 409.8 mg tablets (dogs), 135 mg, 270 mg suspension (cats) | All household animals need to be on lufenuron for effective treatment. Breaks life cycle, no significant adulticidal activity. | Flea infestation | Very safe drug | 10-15 mg/kg once monthly orally with food (D, C) or injectable every 6 months (C). |
Amitraz | ||||
10.6 ml, 50 ml concentrate | Animal must not get wet in between rinses. Animals should not be rinsed when wet. Asthmatic people should not perform the rinse. | Canine demodicosis, cheyletiellosis, scabies and Otodectes cynotisinfestation | Sedation, pruritus, hypothermia, hyperglycemia, hypotension | Mix 10.6 ml in 2 gal of water (D) and rinse q 7- 14 days. Continue for 8 weeks (D) after the first-negative scraping. |
Lyme sulfur | ||||
97.8% sulfurated lime solution | Safe for even puppies and kittens | Cheyletiellosis, scabies, Otodectes cynotisinfestation. Feline demodicosis | Very safe drug | Dilute 1 part to 32 parts water, apply as rinse or dip weekly for 4 weeks (D, C) |
Fipronil | ||||
0.29% spray in 100 and 250 ml bottles, 9.7% solution (0.5 ml, 0.67 ml, 1.34 ml, 2.68 ml) | Spray more effective than spot-on formulation, but strong smell unavoidable during application. For highest efficacy, animals may be shampooed 48 hours before application, but not any sooner; exposure to water does not interfere with efficacy. | Flea-bite hypersensitivity, ticks, possibly scabies and cheyletiellosis | Temporary irritation at site of application, rare hypersensitivities. Contraindicated in rabbits | Spray: 4-6 ml/kg q 2-12 weeks (8-12 pumps using the 100 ml bottle, 2-4 pumps using the 250-ml bottle). (D, C) Spot-on: Apply once monthly |
Selamectin | ||||
15 mg, 30 mg, 45 mg, 60 mg, 120 mg, and 240 mg tubes. | Cosmetically appealing, disperses quickly. Too early to comment further at time of writing | Flea-bite hypersensitivity, Otodectes cynotisinfestation, scabies, heartworm prevention, roundworm, and hook-worm infestations | Focal alopecia (reversible) | 6-12 mg/kg monthly as a spot-on. (D, C) |
Imidacloprid | ||||
9.1% solution (0.4 ml, 0.8 ml, 1 ml, 2.5 ml, 4 ml tubes) | Frequent shampoo therapy or water exposure will significantly decrease efficacy. Solvent may discolor lacquer on furniture. | Flea-bite hypersensitivity | Focal alopecia | 0.4 ml (C)< 4 kg, 0.8 ml (C) > 4 kg. 0.4 ml (D) > 5 kg, 1 ml (D) 5-10 kg, 2.5 ml (D) 10 – 25 kg, 4 ml (D) > 25 kg |
Pyrethrin | ||||
Sprays and powders at 0.05-0.2% | Repellent as well as adulticide. Low toxicity potential, salivation in cats | Flea-bite hypersensitivity | Ptyalism, tremors, ataxia, vomiting, depression, hyperaesthesia, seizures, dyspnea | Use q 24-72 h (D, C) |
Permethrin | ||||
Sprays, spot-ons and shampoos at 0.2-2% | Repellent as well as adulticide. Low toxicity in dogs. Not to be used in cats! | Canine flea-bite hypersensitivity | Ptyalism, tremors, ataxia, vomiting, depression, hyperaesthesia, seizures, dyspnea | Use q 3-10 days (D) |
Insect Control Trials and Individual Management of Patients with Flea-bite Hypersensitivity
Flea control trials
> Treatment recommendations will vary significantly with individual situations. Confirmed flea-bite hypersensitivity, suspected flea-bite hypersensitivity, or pets that show no sign of discomfort, but have some fleas, are treated very differently.
> Reasonably safe and effective products are available (Table 3-7). As veterinarians, we are in the best position to advise clients on a flea-control program tailored to their specific needs that considers their personality and life style as well as their pet's little peculiarities.
♣ A major reason for failure of flea control programs is owner compliance. They are either unwilling, not educated properly, too careless, or simply not physically able to do what we ask them to do for whatever reason. Choosing the right protocol and educating owners properly, taking the time and possibly using nursing staff, brochures, and message boards will greatly increase your chance of success.
‡ With all topical products, the first application should be administered in the clinic by the veterinarian or the veterinary technician/nurse to demonstrate the correct procedure to the owner.
> Another reason for failure may be resistance of the organism to the products used. Resistance will always develop to any product, the question is thus not if, but rather when. In essence, we speed up evolution and create resistant fleas by putting pressure on the population when using products for flea control. However, there are ways to delay this development of resistance. The first possibility is to combine different flea products, as it is much less likely that an individual flea gets resistant to two drugs at the same time. This approach is called integrated flea control and is becoming more popular all over the world. The second possibility is to switch products quickly when signs of resistance occur and kill the resistant flea with another effective product before it has time to multiply in big numbers.
> Suspected flea-bite hypersensitivity: Aggressive flea control is needed for 4 to 6 weeks. If there is no improvement, we most likely do not deal with flea-bite hypersensitivity. With significant improvement or remission, we established a diagnosis and need to discuss long-term strategies with that particular owner. In such a trial, we usually recommend the frequent use of an adulticide in combination with an insect growth regulator in the environment to quickly lower the flea pressure (Table 3-8 and table 3-9).
> Confirmed flea-bite hypersensitivity: Ideally, we recommend an insect growth regulator/insect development inhibitor on a permanent basis (systemically, topically or in the environment) and an adulticide as needed (Tables 3-8 and 3-9). The second option is an adulticide only, in which case we need to switch products very quickly at the first sign of resistance. However, as adulticides are tapered slowly to identify the longest possible interval in between applications, recurrences may indicate insufficient frequency of application rather than resistance.
> No flea-bite hypersensitivity present: In these cases, we do not recommend flea control because permanent flea exposure may be less likely to induce flea-bite hypersensitivity than off-and-on flea control by an owner who is not pressed into compliance by an itchy pet. If the client does want to start some sort of flea control, insect growth regulators or development inhibitors are recommended.
Mosquito-bite trial
The safest and most thorough mosquito-bite trial in cats with papules and crusted papules on nose, pinnae or foot pads is to keep the patient indoors for 2 weeks. When there is no exposure to mosquitoes, the disease regresses rapidly. However, in cats used to outdoors this option may not be viable. Alternatively, exposure is decreased when outdoor activities are limited and cats are trained to come in before dawn by feeding them in the late afternoon. In addition, a mosquito repellent safe for use in cats such as pyrethrin spray may be applied by wetting a cloth and wiping the feet and head daily before the cat goes out.
Table 3-8 Administration, Advantages, and Disadvantages of Selected Flea Control Products | |||
Administration | Advantages | Disadvantages | Comments |
Insect growth regulators/development inhibitors | |||
Fenoxycarb | |||
Indoors: spray q 12 m. Outdoors: Spot treatment of allergic pet's favorite spots q 6-12 m in dry environments. | Comparatively safe and effective, rapid onset of action | Work-intensive | Foggers are more convenient but do not cover more than 2 rooms/can. The insecticide stays on shelves and furniture, but areas underneath furniture are not covered! Sprays are less convenient and more work-intensive, but insecticide is deposited only where needed. Use in all rooms with pet access! Carpeted areas, crevices, and corners as well as areas underneath furniture are most important. Indicated with frequent visiting animals not on flea control as well as at the start of an insect-control trial. |
Lufenuron | |||
10-15 mg/kg q 30 d orally (D), 25-50 mg/kg SC q 6 m (C). | Convenient, safest environmentally | Expensive in multi-pet households, lag period of several weeks to months. | Indicated in house-holds with few pets and no visits from animals without thorough flea control. |
Methopreneor Pyriproxifen | |||
Indoor spray q 6 m | Comparatively safe and effective, rapid onset of action. | Work-intensive | Foggers are more convenient, but do not cover more than 2 rooms/can. The insecticide stays on shelves and furniture, but areas underneath furniture are not covered! Sprays are less convenient and more work-intensive, but insecticide is deposited only where needed. Use in all rooms with pet access! Carpeted areas, crevices, and corners, as well as areas underneath furniture most important. Indicated with frequent visiting animals not on flea control as well as at the start of an insect-control trial. |
Adulticides | |||
Fipronil | |||
0.29 g/100 ml, 10-15 mg/kg as a spray distributed over the whole body q 2-8 week, spot-on q 2-8 week | Water-proof (but not shampoo proof!), convenient, because used only every 2-4 weeks | No repelling action, expensive in large animals, viable egg production possible. | Spray needs to be applied carefully, covering the animal's whole body. Spot-on formulation easier to apply, but less effective. Administer outdoors or in well-ventilated area due to strong smell during first minutes. Shampoo only 2 days before new application. |
Imidacloprid | |||
100 mg/ml | Convenient, because used only every 2-4 weeks, easy to apply | Not water proof, no repellingviable egg production possible. | Shampoo only 2 days before new application. Swimming or roaming in rainy weather not recommended. |
Nitenpyram | |||
Tablets q 1-2 d or as needed | Convenient, rapid onset of action, safe | Flea needs to bite animal to die, only effective for less than one day | May be given daily with no adverse effects. Particularly useful for prophylactic administration in animals on lufenuron directly before anticipated exposure in shows or visits. |
Pyrethrin | |||
| Repels insects, quick knock-out | Work-intensive, rare but possible toxicities, depending on product and patient; daily-to-monthly application | Soak animal with sprays (pressure pump sprays may be useful for bigger or long-haired dogs). |
Permethrin | |||
744 mg in 1 ml as a spot- on for dogs <15 kg, 1488 mg in 2 ml for dogs >15 kg. Do not use in cats. | Repelling action, quick knock-out. | Work-intensive, rare but possible toxicities, depending on product and patient; daily-to-monthly application | Soak animal with sprays (pressure pump sprays may be useful for bigger or long- haired dogs). |
Selamectin | |||
6-12 mg/kg monthly as a spot-on | Easy to use, cosmetically appealing, safe | Too new to comment at time of writing. | Too new to comment at time of writing. |
Table 3-9 Application of Selected Flea Products in Patients with Confirmed versus Suspected Flea-bite Hypersensitivity | ||
Drug | Confirmed Flea-Bite Hypersensitivity* | Suspected Flea-Bite Hypersensitivity* |
Fipronil spot-on | q 2-4 weeks | Not used for insect control trials |
Fipronil spray | q 4 -12 weeks | q 7-14 d for 4-6 weeks* |
Imidacloprid spot-on | q 4 weeks | q 7-14 d for 4-6 weeks* |
Nitenpyram | In addition to lufenuron, when patient shows clinical signs or before suspected exposure | q 1-2 d for 4-6 weeks* |
Permethrin spot-on | q 4 weeks | Not used for insect control trials |
Permethrin spray | Varying depending on individual product up to q 7-14 d | Varying depending on individual product up to q 2-3 d for 4-6 weeks* |
Pyrethrin spray | Varying depending on individual product up to q 7-14 d | Varying depending on individual product up to q 2-3 d for 4-6 weeks* |
Selamectin | q 4 week | q 14 d for 4-6 weeks* |
* In any flea control trial adulticides are combined with an insect growth regulator used in the environment at the beginning of the trial. |
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Department of Clinical Sciences Coll. of Veterinary Medicine & Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
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