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Regional topical therapy in the management of pruritic skin disease

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01 February 2013, at 12:00am

SUE PATERSON reviews a cost-effective treatment that enables a reduction in the need for systemic medication but stresses that careful assessment is critical in each case

TOPICAL therapy is often overlooked in the management of allergic skin disease in dogs and cats. Even though veterinary surgeons now have access to an ever increasing armoury of anti-inflammatory medication, topical therapy especially for localised problems can make a big difference to the level of comfort of our patients.

Not only is it cost-effective but it also allows us to reduce the levels of systemic medication, whether it is glucocorticoids, cyclosporine or antibiotics. Careful assessment of each case is critical to decide on the most appropriate form of treatment. All animals should be checked for ectoparasites and should have a properly performed food trial undertaken with either a home-cooked or hydrolysed diet.

Cytology of the skin is also important to check for bacterial or yeast infection. In the author’s practice each animal has cytology performed from a wide range of different areas (see Table 1).

The type of extensive cytological investigation described in Table 1 is time-consuming and cannot really be undertaken successfully in a normal consultation. It is therefore important to get animals into the surgery at a time when adequate diagnostic investigations can be performed.

Many of the allergic dogs that present to clinicians have mild to moderate generalised itch but more intensive regional itch. Often this is due to localised infections or an ectoparasitic problem. Typically these cases improve when, for example, cyclosporine is prescribed but are often left with marked regional itch such as pedal pruritus, perianal irritation or facial discomfort.

Careful cytological assessment of these animals often identifies specific problems (Table 2) that can be managed by the addition of selective topical therapy.

In this disposable, convenience age, owners often request systemic therapy because of its ease of administration, with little appreciation of the long-term consequences of inappropriate drug usage.

It is thus pertinent to spend a few moments to explain to owners why responsible drug usage is a necessary if sometimes difficult option, so they realise why it is important to use topical antibacterial products rather than a systemic antibiotic or a topical steroid spray rather than a long-acting steroid injection. 

Topical therapy is always more labour intensive but often after an intensive period of daily application of a product, its administration can be reduced to once or twice weekly application making life more bearable for an owner.

A wide range of topical antibacterial and anti-yeast products are available to manage areas where cytology has identified colonisation of the skin with bacteria or yeast. Topical agents with anti-yeast activity include boric acid, chlorhexidine and miconazole. Topicals with antibacterial action include acetic acid, benzoyl peroxide, chlorhexidine, chloroxylenol and ethyl lactate. These are available as shampoos, sprays and wipes (see Table 3).

When using these types of products, clinicians should obviously be aware of the concentration of the different components in them and whether they are licensed or unlicensed veterinary products. Where a product is licensed for use, it has obviously been shown to have specific medicinal properties which enable the manufacturers to make medicinal claims on the bottle such as activity against Staphylococcus spp. or Malassezia spp.

A typical example as to how topical therapy can help to manage a case may be where a young Labrador dog presents with generalised pruritic skin disease well controlled with ciclosporine but has residual pedal pruritus. Cytology from the interdigital area reveals large numbers of Malassezia yeast (Figure 1).

The addition into the dog’s treatment regime of daily cleansing of the interdigital areas with an antiseptic wipe, spray or shampoo to treat the yeast leads to resolution of the pruritus and excellent overall control. After daily treatment for seven days, the owner is able to switch to twice weekly therapy for maintenance.

Additional therapy

Where regional pruritus fails to identify any significant ectoparasitic or infectious component, additional localised antipruritic therapy may be considered almost to “top up” the systemic therapy. Localised anti-pruritic therapy may take many forms.

Topical agents act in a variety of ways to help reduce pruritus. Often just the physical action of shampooing the skin helps to soothe it and the use of gentle exfoliating agents such as alpha hydroxyl acids can remove pruritic mediators.

Some products such as camphor, thymol or menthol act to replace the sensation of itch with cold or heat. Others such as oatmeal and aloe vera are thought to reduce the formation of inflammatory mediators and hence produce anti-inflammatory effects. Benzoyl peroxide and tar are described as having local anaesthetic effects.

Moisturising agents that can help soothe itch are glycerine and urea. When these more “natural” products fail to control itch then topical glucocorticoids may provide relief and are obviously preferable to increasing systemic medication. These types of product should be used with care to maximise benefits and minimise the side effects.

Where their use is excessive and certainly where it exceeds the recommended usage by the manufacturers, it may be better to increase the levels of systemic therapy as safely as possible rather than risk side effects from topical therapy.

Potent topical steroids such as betamethasone, dexamethasone and hydrocortisone aceponate should be used on an occasional basis and clinicians should be guided by the manufacturers’ recommendations. 

Gel and spray formulations are preferable to creams and ointments as the latter two tend to be more persistent and occlusive. Betamethasone-based gel is licensed for use for a seven-day period; it is therefore most useful for animals that have acute allergic flares where the addition of a potent glucocorticoid can rapidly damp down pruritus.

Where it is needed for repeat courses on a regular basis, it is probably not the best drug choice as prolonged usage can lead to systemic absorption and cutaneous atrophy. Hydrocortisone aceponate spray is similarly recommended as therapy for a seven-day period.

However, clinical work has shown that even though it is unlicensed for use for more than a week, it can be used for more prolonged periods (Nuttall, 2009 and 2012). Generally the author will use it on small localised areas three days out of seven; if it is needed for more frequent use it may be better to consider adjusting systemic therapy.