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.
