Treatment for mites and lice in the rat

by "Matmor" in collaboration with Professor Nils Søli at Norges Veterinærhøgskole (The Norwegian Veterinary College) and the Norwegian Fancy Rat Society (NTF)

This is the first part of a survey as published in the Norwegian Fancy Rat society's periodical Gnag, and part II as pre-print. Part III will appear later. Thanks to Sheila Sowter for helping me sort out the "Norwenglish"! The spelling mistakes are my own...

Part I of III

From April 2004 up to and including April 2009 seven different users of The Norwegian Fancy Rat Society (NTF)’s forum reported side effects from treatment for mites and lice. Three of the seven cases resulted in one or more deaths. Probable signs of poisoning (cramps, problems with coordination and balance) were observed in two cases. In the third case symptoms were not observed but a young rat was found dead in its cage on the morning after treatment. The dead rat was already weakened by the infestation of lice. There were also postings about treatment resistant mites.

In a former survey for NTF1 infestations of lice and mites were the most common causes for rat owners to seek veterinary advice. No drug for rats has marketing approval, neither for treating lice, mites, nor other maladies. Considering the seriousness of the side effects, users of NTF’s forum, Råttforum in Sweden and Tamrotten in Denmark were asked to fill in anonymously a net based form with questions about treatment for lice and rats. The form can be seen at (Norwegian version only). The prospective participants were asked to fill in the form regardless of treatment outcome. It was explained that information about treatmens which are safe and effective is just as valuable as information about lack of effect or side effects.

The survey had questions regarding

Ultimately our aim is to find safer and more effective treatments.


The survey was open for a month. During this time we had 25 contributions representing more than 368 rat courses of treatments. A rat course of treatment (RCT) was defined as the full dosage intended to cure one rat. The number is somewhat uncertain: ”more than” because some of the contributors had used this wording in their replies. Judging from the number of rats that were reported as ”cured”, and how many rats that were reported ”not cured” there were actually ”more than” 395 rat courses of treatment. Some of the contributors had had trouble understanding what was meant by ”rat course of treatment”, even if this was explained with examples on the form.

Nine of 25 replies had information about side effects, two about failed cures.

Two replies to the survey alone represented (>) 150 rats. Both replies concerned Frontline.

Table 1: Drugs recorded in the survey
Drug TotalSide effectsPoor effect
repliesRCT% RTCrepliesrats
321 (47)5,7 (11,9)
[5,3 (11,8)]
Imidlaclopride and
3Not stated1
426 (27)7
11129 (>130)35
The veterinary drugs were Advantage spot-on, Advocate spot on for cats, Frontline spot-on and spray, Ivomec injection, mixture and oral paste, Stronghold spot on 120 and 60 mg/ml. The percentage is calculated from 368 [and 395], see text in the paragraph above as to why two different values are given.

As no veterinary drug for rat has a marketing approval there are no officially recommended treatment regimes. Even so the use of fipronil, ivermectin, selamectin, and permethrin to combat lice and mites in the rat has been described in scientific litterature. Concerning permethrin the use of dusting powder cannot be compared to Exspot. The uptake would most certainly be very different. Otherwise the litterature describes the use of drugs with a marketing approval for other species than rat. We did not find any scientific literature about the use of Imidacloprid against lice and mites in the rat. The recommendations are by Florida Rat and Mouse Club of America in collaboration with a vet.

Table 2: Use and reccomended use
DrugConfirmed useReccomended useSource
Advantage spot-on 100 mg/ml1 dr./500 g rat1 dr/450 g rat,
½ dr for small rats < 4 months
Advocate spot-on 100 mg/ml + 10 mg/ml1 dr./500 g rat1 dr/450 g rat,
½ dr for small rats < 4 months
Exspot* spot-on 744 mg/ml0,06 ml adult females
1-2 dr. pups
Frontline spot-on 100 mg/ml2 dr./200 g rat1 dr/adult rat strength not given but probably spot-on9
Frontline spray 2,5 mg/ml1 spray (0,5 ml)/250 g or 500 g rat
Not stated
1 spray/rat5
Ivomec inj. 10 mg/mlNot stated 100-200 µg/lb oral, subcutaneous, or dermal application
Dermal: 1 dr. of a solution of 10 mg/ml injection diluted 1+99 in 50% water 50% propylene glycol
or 200-400 µg/kg orally, SC or behind the ear after diluting 1+9 with propylene glycol
2, 3, 8
Ivomec paste horse0,5ml/250g rat (1 case), otherwise not stated pr. 450 g rat: An amount equal to a boiled grain of rice
< 450 g rat: equal to ½ boiled grain of rice
Ivomec mixture 0,8 mg/ml sheepNot statedoral: 0,125 ml/500g dermal: 0,250 ml/500g
in drinking water : 8 mg/L 24 hours
Stronghold spot-on 60 mg/ml
(dosage for 120 mg re-calculted as 60 mg)
1 dr./100 g rat, 2 dr./500 g rat
(6 replies without dosage given by weight)
1 dr./100 g rat, 1 dr. pr. rat2,4,6
* Exspot was not recorded in the survey, only at NTF’s forum. Dosages resulting in cramps or death have been marked in bold red print.

Part II

Part I (in the former issue of Gnag) concerned itself with the reported dosages. Part 2 is about the reported treatment intervals, side effects, and dosages for rat pups/pregnant or nursing does.

According to the survey, the course of treatment sometimes consisted of one application only of Frontline, Ivomec, or Stronghold. The two drugs for lice and mites for which treatment failed in the survey were Frontline and Stronghold (one report for each remedy). At NTF’s forum treatment failure was reported for Ivomec. In all reports of poor efficacy the treatment was given the recommended number of times according to the listed sources.

Table 3: Number of applications per rat and interval
Veterinary drugSurveyRecommendation
No. applicationsIntervalNo. applicationsIntervalSource
Advantage221 d1 or more-/30 d2,7*
Advocate2-321 d1 or more-/30 d7*
Exspot?(1)?1 or more-/7-30 d7*
Frontline1-2-/14 d1 or more-/28 d5,7*
Ivomec1-3-/10 d37-14 d2, 3, 8
Stronghold1-310-212 or more14-30 d2, 4 6
7 is for dog and cat. Advantage and Advocate is reported to protect against re-infestation by fleas for three to four weeks. The treatment interval is set at 30 days if needed. Frontline is reported to protect against ectoparasites (dog or cat) for four weeks.

The case of treatment failure for Frontline applied to the spray, not to the spot-on product. It is possible that the spray dosage is too low to reach the necessary concentration to kill lice and mites when treating large rats, see mg/m2 in table 3. Most likely it is the concentration of the drug in skin fat that kills vermin, not the dose in mg/kg. (Square meter animal has been computed from Meeh’s formula.)

Table 4: Dosage of fipronil 1 spray per rat
SprayRat mg/kgRat mg/m2SprayDog mg/kgDog mg/m2
100 g rat12,565,710 kg dog7,5-15161-322
500 g rat2,522,760 kg dog7,5-15293-585

Side effects

None of the participants in the survey used the ”other”-category for side effects. The reported side effects are mostly in accordance with side effects observed in rats during toxicological testing, but diarrhea, for example, was not recorded. On the other hand the toxicological reports do not mention nasal noises. This was reported by several contributors. It is impossible to say if the noises were due to stress, lowered immunity, or increased secretion of mucous.

The survey did not report deaths connected to treatment. A search at NTF’s forum showed that in two of the three cases with resulting death, an excessive dose was administered compared to the recommendations in Table 2.

The table below presents all reported side effects, both from the survey and from NTF’s forum.

NB! The number of rats refer to the survey only, not treatment mentioned in forum posts.

Table 5: Side effects of the veterinary drugs
Veterinary drugSide effects reported in the surveyRats with side effects (survey)Side effects reported on the forum
Redness, necrosis, nasal noise, tiredness>2 of 47-
(imidacloprid, moksidektin)
-0 of 12-
Redness, discolouration, abscess, nasal noise, cramps, imbalance, confusion, agitation, tiredness, poor appetite? of 180Cramps, death
Redness, hair loss, agitation, tiredness, poor appetite 2 of 27Necrosis, porphyria, imbalance, lethargy, breathing problems, death (acute euthanisation)
Nasal noise, discolouration2 of 130Seborrhoeic eczema
--Cramps, psychotic behaviour, death

Side effects from skin and hairs were reported for Advantage (redness and necrosis, one report), Frontline spot-on solution (redness, discolouration, and abscess, one report), Ivomec paste (redness and hair loss one report, overdose), and Stronghold (discolouration one report). At NTF’s forum there was an additional report of a skin reaction to Stronghold: seborrhoeic eczema, and one report of necrosis after the administration of Ivomec injection.

Cramps, imbalance, confusion, and agitation was reported for Frontline spot-on (cramps, imbalance, confusion one report, overdose), for Frontline spray (confusion, agitation one report), and for Ivomec paste (agitation two reports, overdose in at least one report). Additionally cramps, psychotic behaviour, and death was reported on NTF’s forum following administration of Exspot (overdose). Cramps were also reported after administring Frontline spray, dosage unknown. More general side effects like tiredness and a low appetite was reported for Advantage (one report of tiredness), Frontline spot-on (tiredness and poor appetite one report, overdose), and Ivomec paste (tiredness and poor appetite one report, overdose, and lethargy one report).

Nasal noise was reported as side effect in four out of 25 reports. These reports addressed Advantage (two cases), Frontline spray (one case), and Stronghold (one case).

Treatment of rat kittens

The survey did not ask for information on treatment of pregnant or nursing does. Most of the rats in the survey were above 5 weeks. Only 26 RCT were registered in this category, but the kittens still represent 7% of the total number of rats. In rat kittens, Frontline spray was registered with 14 rat courses of treatment, and with 12 RCT Stronghold spot-on. No side effects were reported for rat kittens in the study. On the other hand there were reports of lethal side effects of Exspot (”rat kittens”) and Frontline (a ”freshly acquired” rat) at NTF’s forum, no exact age given. According to the recommendations in Veterinærkatalogen none of the drugs are contra-indicated for nurslings, although rat kittens are not mentioned. Conciveably rat kittens are more likely to experience side effects from dermal treatment than dog, cat, sheep and horse, as dermal absoption from rat skin is generally higher than for the larger mammals. On the other hand reproductive toxicity is frequently more closely studied in rats than in other mammals.


  2. Florida RMCA (Rat and Mouse Club of America)
  3. Handbook of rodent and rabbit medicine (Pergamon Veterinary handbook series) , ISBN: 9780080425047
  4. Efficacy and Safety of Selamectin (Stronghold®/Revolution™) Used Off-Label in Exotic Pets, Fischer et al. Intern J Appl Res Vet Med • Vol. 5, No. 3, 2007 pp. 87-96
  5. Efficacy of fipronil in the treatment of pediculosis in laboratory rats, S. L. Diaz, Laboratory Animals (2005) 39, 331–335
  6. Torunn Sørbye (personal communication)
  7. The Internet version of ”Felleskatalogen over preparater i veterinærmedisinen 2008-09” Oct. 1 st. 2009
  8. Elimination of an Infestation of Rat Fur Mites (Radfordia ensifera) from a Colony of Long Evans Rats, Using the Micro-dot Technique for Topical Administration of 1% Ivermectin
    Condo et al. Contemp Top Lab Anim Sci. 1998 Jan;37(1):58-61.
  9. Advances in Veterinary Dermatology, vol. 5
    selected papers from the Fifth World Congress of Veterinary Dermatology, Vienna, Austria, 25 - 28 August 2004.

Matmor original 2010.04.19
last changed 2010.07.22
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