Management of the pruritic cat: Topical and systemic (Proceedings)

The symptomatic treatment of feline pruritus is often complicated by the multiple predisposing causes including allergy, dermatophytosis, parasitic, viral, autoimmune and neoplastic diseases. Treatment is complicated by the frequent difficulties in administering oral medications and the excessive grooming associated with topical medications. Transdermal route of administration of medications may be considered. Glucocorticosteroids continue to be the primary treatment although there ay be some serious complications with prolonged use. Antihistamines, cyclosporine, Leukeran and fatty acids may be efficacious. There are several classes of medications that are used for treatment of pruritus.

Glucocorticoids:

Methylprednisolone acetate (Depo-Medrol® is frequently administered as the first antipruritic medication, especially in cats that are difficult to treat orally. Multiple injections at 2-3 week intervals are often required to bring about a temporary resolution of the symptoms associated with the eosinophilic granuloma complex, food allergies or atopy. The average dose is 20mg/cat or 4 mg /kg SC. The duration of symptomatic relief of the pruritus is variable from 2 to 6 weeks.. It is common to observe less or shorter intervals of response with repeated injections requiring more frequent injection intervals.

Oral prednisone, prednisolone or methylprednisolone are the most widely used short-acting glucocorticoids. In general, cats require twice the dosage compared to dogs to control pruritus. The initial dose is 1-2 mg/kg/day. In severe cases 3-5 mg/kg/day may be needed, especially those caused by autoimmune dermatoses, severe eosinophilic granuloma complex or food allergies. Tapering doses and alternate day therapy is recommended. The response to oral glucocorticoids is variable with a rather high frequency of inadequate response.

Oral dexamethasone is indicated in those cases that do not respond to the shorter-acting steroids. The recommended initial dose is 0.1-0.2 mg/kg/day. Maintenance doses are usually 0.05-0.1 mg/kg q2-3 days. If the lesions are controlled with the maintenance doses of dexamethasone, it is indicated to substitute short-acting glucocorticosteroids to minimize adverse reactions.

Triamcinolone acetonide (Vetalog®) may be useful when a short course of glucocorticoids is indicated. The dose is usually 0.1-0.2 mg/kg IM or SC. The therapeutic effect is usually a maximum of one week.

Antihistamines:

Antihistamines are often the first drugs of choice although the efficacy of antihistamine therapy is often low. The incidence of serious adverse reactions is very low. Chlorpheniramine is the most commonly used antihistamine. Recommended doses are 2-4 mg/cat PO q 8-24 hours. Transient drowsiness is the most common adverse reaction that is usually dose-dependent. Hydroxyzine (Atarax® may be administered at a dose of 1-2 mg/kg q8-12 hr. Hyperexcitability or depression may be observed. Clemastine (Tavist®) is also used at a dose of 0.15-0.68 mg/kg q12 hrs. Some synergism with essential fatty acids has been reported.

Essential fatty acids:

Omega 3 (n-3) fatty acids are the most widely recommended fatty acid supplements. Some are combined with Omega 6 (n-6) fatty acids. There is a reported 50-75% improvement in some cats with miliary dermatitis or eosinophilic granuloma complex lesions. Palatability is a common problem. Four to six weeks of therapy may be needed before clinical improvement is observed.

Immunomodulators:

Cyclosporine (Atopica®) is used as an off-label drug for treatment of eosinophilic granuloma lesions and allergies. The average dose is 25 mg/day/cat. Some cats will require twice a day dosing initially. It is generally well-tolerated. Loss of appetite and vomiting are the most common adverse reactions. It is recommended to test for viral diseases and toxoplasmosis prior to initiating therapy due to the potential for immunosuppression.

Chlorambucil is indicated in cases which have not responded well to glucocorticoid or cyclosporine therapy or in cases that require a high maintenance dose. Chlorambucil is frequently used concurrently with glucocorticosteroids when treating pemphigus foliaceus. It is generally well-tolerated at a dose of 0.1-0.2 mg/kg q24 hrs. Since bone marrow suppression may occur, periodic CBC and platelet monitoring is indicated.

Specific therapies:

There are several causes of pruritus that require a more specific type of medication including antiparasitic and antifungal agents.

Fipronil (Frontline®) is an effective treatment for Otodectes, Cheyletiella, fleas and ticks.

For Otodectes, instill two drops in each ear canal without cleaning. Apply the remaining contents of the applicator on the skin. Use two doses at 2 week intervals. Two doses of either the spot-on or spray at two week intervals is an effective treatment for Cheyletiella. Fipronil may use on kittens over 2 days old.

Selamectin (Revolution®) is an effective treatment for Otodectes. One dose is usually required. Adverse reactions are rare. Transient alopecia, local irritation at the application site and digestive upsets are reported to occur 1% of the cases.

Ivermectin may be used for Cheyletiella, lice, Notoedres and Otodectes. The dosage is 200-400 ug/kg SC. One or two doses are required at 2-4 week intervals. Do not administer to kittens < 4 months old. Toxicity is rare occurring most often in kittens. Ataxia, lethargy, weakness, recumbency, apparent blindness, coma and death has been seen 1 to 12 hours after administration of the medication.

Lime sulfur 2% solution is a recommended treatment for feline demodicosis, Malassezia, Notoedric mange and dermatophytosis. It is inexpensive and nontoxic. Side effects include occasional excessive drying and or irritation of the skin. Cosmetic issues include a disagreeable odor, temporary yellow staining of skin and hair as well as staining of clothing and tarnishing jewelry. Lime sulfur solutions are used twice weekly for Malassezia infections and every 5-7 days for dermatophytosis, Notoedres and demodicosis. Treatment is often continued for 6-8 weeks in many cases.

Griseofulvin is used as a treatment for dermatophytosis. The dosage is variable from 25-50 mg/kg bid (microsized) or 5-10 mg/kg SID (ultramicrosized). Do not use in FIV positive cats because of the possibility of severe neutropenia. Adverse effects may include vomiting, diarrhea, anorexia and bone marrow suppression. Griseofulvin is teratogenic. Several months of treatment is usually required until there are two negative cultures at 2-3 week intervals.

Itraconazole is often the antifungal agent of choice for dermatophytosis. The clinical response is usually shorter than griseofulvin. The most common dose is 10 mg/kg SID PO, However a dose of 3-5 mg/kg SID reported to be effective. Pulse therapy with a daily dose administer 2 consecutive days each week is also reported to be effective. There are minimal side effects which include rare hepatoxicity. Itraconazole is teratogenic.

Lufeneron has been used as a treatment for dermatophytosis. The recommended dosage is 100mg/kg q24 hrs. There cure rate is reported to be 70-80% with a 20% relapse. Lufeneron is well tolerated.

Hyposensitization is a valid option for managing feline atopy. The effectiveness of allergy injections based on a >50% improvement of pruritus is generally 60% to 70%. A time lapse of 6 to 8 months may occur before the maximum clinical response is achieved. Antihistamines, cyclosporine or glucocorticoids are used concurrently with hyposensitization if needed to help control the pruritus.

Transdermal therapy:

Transdermal route of administration may be a viable alternative for the cat that is difficult to treat with oral medications. The pharmacokinectics are seldom known. Some of the variables include rate of absorption, optimum doses and frequency to achieved blood levels and the molecular weight which will pass through modified barrier. Compounding pharmacists apply guidelines used in humans for animal prescriptions.

There are a relatively few dermatologic drugs that are absorbed well via the transdermal route. The drugs reported to be effective with transdermal preparations include clindamycin, cephalexin, fluoxetine, amitriptyline, chlorpheniramine, and prednisone.

The transdermal delivery systems alter epidermal barrier and modify the intercellular lipids surrounding the corneocytes. These activities allow larger molecules to pass through the epidermal barrier. The delivery system utilizes vehicles which modify the barrier and attach active ingredients but do not modify the active ingredient. Most medications are compounded using the same dosage and frequency as recommended for the oral route of administration. They are usually applied to the medial pinnae or ventral abdomen/medial thigh.

The management of the pruritic cat can be challenging. Frequently multiple therapeutic modalities are used concurrently to help control pruritic symptoms.