Manejo Médico del Prurito

Pruritic skin diseases are perhaps the most frequent reason for consultation in daily clinical practice, therefore it is important the role of antipruritic drugs, a minimum knowledge of each one of them and the stage of the pathology in each patient.

When itching is mentioned, immediately we think about allergies and sarcoptic mange, then we will focus primarily on the use of antipruritic drugs in these pathologies.

The pathophysiology of itching is exciting and considerable knowledge has been achieved in recent years including the emergence of new antipruritic drugs. We will not focus on this subject because it is too extensive and exceeds the time available for this conference.

Corticosteroids

Corticosteroids are still on the first line of drugs used to control itching. The immunomodulatory and antipruritic properties of these drugs generate a quick profit in pruritic skin diseases and many other extracutaneous diseases.

Side effects should not be overlooked; nevertheless, its rational use would lead to acceptable results with minimal side effects.

Corticosteroids are well absorbed orally and are widely distributed throughout the body, being eliminated by the kidney and liver.

The different corticosteroid molecules differ between them in efficacy, antiinflammatory potency, onset of action, plasma half-life and duration of action.

In extended antipruritic therapies, it is recommended to use molecules with lower toxicity and shorter time of action as prednisone, prednisolone and methylprednisolone.

On the web there are convertors to change the dose from one type of corticosteroid to another. One of them is www.medcalc.com/steroid.html.

Antihistamines

Antihistamines block histamine receptors but are less effective and are not suitable for the treatment of acute pruritus. They may be useful for maintenance in chronic therapies in order to reduce the dose of corticosteroids, although there are several studies reporting no difference between treated and control animals.

There are 7 groups of antihistamines. The most frequently used are: hydroxyzine, chlorpheniramine, oxatomide and diphenhydramine. However, clemastine, cetirizine and loratadine are also used.

Cyclosporine

It is an immunomodulatory agent; its mechanism of action is based primarily on the inhibition of calcineurin, and thereby inhibiting the activation of T cells (inhibits Langerhans cells and lymphocyte function and function of effector cells in the allergic response such as mast cells and eosinophils).

It has few side effects and achieves therapeutic effect 10–20 days after beginning of treatment. The dose in dogs is 5 mg/kg/day for a month and then administration could become less frequent until a minimum effective frequency is established.

Oclacitinib

It has been proven to be safe and effective in reducing itching by inhibition of the pathways involved in its development and the inflammation associated with allergy. It is a selective inhibitor of cytokine depending on Janus kinase enzyme. Also, it inhibits IL-31 function, which plays a major role in atopic dermatitis.

The recommended dose is 0.4–0.6 mg/kg orally every 12 hours for 14 days. Maintenance is continued with the same dose but the frequency is reduced to once daily. Side effects that can be observed are vomiting, diarrhea and anorexia.

Specific Allergen Immunotherapy

In those dogs in which it is feasible to perform skin test or serology for allergies could be very useful to do ITAE.

Although success rates vary in most studies, 60% of the cases reach a good response. The response to treatment is slow and generally results are observed 6 months after beginning of treatment.

Essential Fatty Acids (EFAs)

They are useful in the maintenance of chronic therapies since the effect is long term because it requires incorporation into cell membranes. They are not useful for the acute treatment of pruritus.

Baths

A shampoo that does not irritate or damage the skin should be used. Shampoos which are effective include those containing lipids, complex sugars and antiseptics. Although actually what is estimated that improved the effect is the action of natural water on the skin for several minutes, this produces an antiinflammatory effect and removes allergens from skin surface.