Small Animal Dermatology, 3rd edition

CHAPTER 19 DEMODICOSIS (CANINE AND FELINE) 301

Between 11% and 30% of cases will not be cured; may need to try an alternative

therapy or control with maintenance dips every 2–8 weeks.

 Ivermectin:
Off-label use for demodicosis
Macrocyclic lactone with GABA agonist activity
Binds to chloride channels in the mite’s nervous system, causing paralysis and

death

Safety in mammals is due to the lack of glutamate-gated chloride channels in

the peripheral nervous system and the restriction of GABA-gated channels in

the central nervous system (which is protected by the blood–brain barrier)

Contraindicated in collies, Shetland sheepdogs, Australian shepherds, Old

English sheepdogs, white German shepherds, long-haired whippets, grey-

hounds, silken windhound, other herding breeds, and crosses with these breeds

Ivermectin sensitivity: derived from a deletion mutation of the multidrug-

resistant gene (ABCB1) resulting in a truncated nonfunctional protein called

P-glycoprotein; P-glycoprotein is a transmembrane protein transporter found

in the blood–brain barrier; P-glycoprotein pumps ivermectin within the

brain back into the blood; testing for this mutation is available through

the Washington State University Veterinary Clinical Pharmacology Laboratory

(www.vetmed.wsu.edu.vcpl)

Toxicity seen as hypersalivation, mydriasis, tremors, depression, ataxia,

blindness

Intravenous lipid emulsion therapy has shown success in the treatment of iver-

mectin toxicosis

Do not use with Spinosad-containing flea control products; enhances toxicity of

ivermectin

Demodexotitis can be treated with 0.01% ivermectin solution

Oral administration of the injectable formulation: 0.3–0.6 mg/kg q24h

Administer 120μg/kg q24h for the first 3 days to identify ivermectin-sensitive

breeds (ABCB1 mutation): alternative dosing – gradual dose increase from

0.05 mg/kg on day 1; 0.1 mg/kg on day 2; 0.15 mg/kg on day 3; 0.2 mg/kg on

day 4; 0.3 mg/kg on day 5: continued increases of 0.1 mg/kg daily if necessary to

administer maximum dosage of 0.6 mg/kg q24h

Treat for 60 days beyond negative skin scrapings (average 3–8 months)

Continue rinses for at least 1 month following negative skin scrapings.

 Milbemycin:
Off-label use for demodicosis
Macrocyclic lactone with GABA agonist activity
Dosage of 1 mg/kg PO q24h cures 50% of cases; 2 mg/kg PO q24h cures 85% of

cases; oral dose recommendations range between 1.5 and 3.1 mg/kg/day

Treat for 60 days beyond multiple negative skin scrapings

Ivermectin-sensitive breeds (ABCB1 defect) generally tolerate milbemycin

Side effects are similar to ivermectin (depression, stupor, coma, ataxia, seizures)

Major limitation of the drug is expense

Demodexotitis can be treated with 0.1% milbemycin oxime topical.