IMAGINE the scene. Incarcerated
in a couple of dimly lit rooms, with
20 or so delegates, waiting to learn
about ear disease and topical skin
treatment. All the ingredients there
for one hell of an evening! Did I
really have nothing better to do?
There must be better ways of
spending a Wednesday evening after a
long day at the coal face – collating
one’s CPD records for example. Ah
yes, those CPD records and finding
courses which you don’t have to visit
the bank manager before attending.
Like this one, which was sponsored by
Virbac.
Fortunately, all expectations of
dirge were misplaced on this occasion.
First, the one thing which always
attracts us to these
events arrived – food!
What we hadn’t
expected however was
Dr Filippo De Bellis
or, more accurately for
those of us who had
not met him before, a
typically loquacious
Italian with an
infectious enthusiasm
for dermatology. Unlike
many lecturers on the CPD circuit,
Filippo not only knows his stuff but
he can also communicate such
knowledge to lesser mortals such as
me.
I didn’t envy him the task of
making Topical therapy in dermatology
sufficiently engaging to hold our
interest for nearly an hour but engaged
we were.
He opened with a few remarks on
the pharmacology of topical
treatments, highlighting the
pharmacokinetic factors influencing
the potency of surface acting agents.
Difference explained
Of particular note was the difference
between healthy and diseased skin in
the absorption and efficacy of a drug.
Diseased and inflamed skin has
different absorption properties to
healthy skin, and any concerns over
secondary systemic effects must take
account of this.
Efficacy is also dependant on the
mode of delivery of the drug to the
skin surface. Powders were historically
important – those of us suffering
frontal alopecia or follicular
depigmentation fondly remember what
clients believed was the panacea for all things skin-related – “wound powder”!
These have now fallen from grace with the advent of H&S storm
troopers decreeing any particulate
airborne material to be too dangerous
in the absence of PPE.
Technology has moved on and we
now have emollients, lotions,
embrocations and balms.
Unfortunately, these are now so
effective at penetrating the skin that
the person applying such treatments
with fingers is just as likely to absorb
the actives as the patient. Which
brought us to shampoos.
Twenty-five years ago there were
two types of shampoo kept in most
practices: “anti flea” and
“conditioning”. Now there are around 20 different
therapeutic shampoos,
each tailored to
specific conditions,
and a major
component of any
skin disease
management strategy.
Filippo went on to
explain what all the
various agents used in shampoos were
appropriate for. Much of what he said was known to us but had been stored
in that area of our brain labelled “to
keep for a rainy day” or been sent to
the recycle bin after leaving college.
Pearls to ponder
There were many pearls which made
us think, “Ah that’s why that didn’t
work as well as I had hoped!” For
example, chlorhexidine is a very
effective antifungal agent, but only at
concentrations of at least 2%.
Conversely, when used for open
wounds,
concentrations
above 0.5% can
inhibit granulation
tissue formation.
It was a surprise
to learn that a one
part vinegar one
part water mixture
can kill Pseudomonas
aeruginosa in one
minute, and a
stronger solution
can take care of
coagulase positive
staphs. Filippo was
not specific about
whether balsamic or
cider vinegar was
better – but one
suspects balsamic! I
will need to think
about stocking
Malacetic shampoo and wipes again.
Then there is the favourite of pubescent teenagers everywhere –
benzoyl peroxide. As Paxcutol, it’s well
known to be a first choice antibacterial
shampoo but did you know it can be
very beneficial in the management of
demodicosis, and can be useful for
feline acne?
Of particular interest was the role
of humectants in atopic disease. These
hygroscopic agents maintain skin
hydration, which has been shown to be
a major factor in controlling the
absorption of particulate allergens.
Sprays such as Humilac can therefore
have beneficial effects in atopy. And if
you get desperate, Humilac is not bad
as an antifreeze, as it contains
propylene glycol, sister to ethylene,
and considered the safer alternative.
New generation
A recent advance in the topical arena
is the use of minimally systemic
corticosteroids. Dermatologists have
long been wary of using topical
steroids for fear of significant systemic
effects but a new generation of
steroids, headed by hydrocortisone
aceponate (HCA), look likely to make
them fashionable again.
HCA is slowly biotransformed in
the skin to hydrocortisone with
minimal systemic effects. This means it
is not contraindicated, when used at
the licensed dose and frequency, in
concurrent NSAID use, pregnancy or
diabetes. As Cortavance it has also
been shown to have a consistent
potency irrespective of hair length,
and so can be used on haired skin
without the need for shaving.
Something else new to most of us
was Tacrolimus, a
macrolide in Pro
Topic. This has
great potential in
the treatment of
immune-mediated
disease, particularly
perianal fistulas and
atopic dermatitis.
After a short
break Filippo launched into ear
disease. So a deep
breath and in we
go – anatomy first
and another trawl
through ancient
dormant parts of
the brain. With the
lost files suitably
restored, Filippo
then gave us a
synopsis of otitis
externa covering
the various factors
involved in eliciting ear disease, types of infection,
diagnosis and approaches to treatment.
Did we know that German
Shepherds are prone to ear canal
cartilage mineralisation, and there is a
Japanese ear fibrescope which makes
visualisation of the lower ear
structures much easier? We do now!
When considering treatment
strategies there were several nuggets to
take away. We all know that systemic
agents have a poor penetration into
the ear canal, but few of us knew
frusemide was right up there as a cause
of ototoxicity. Conversely, we were all
taught at college never ever to use
aminoglycosides if there was any
chance of tympanic perforation.
However, Filippo brought our
attention to a study in which no
damage was caused by the direct
instillation of gentamicin into the
middle ear of dogs. Gentamicin, it
turns out, is a very useful topical agent
in the ear.
There is low incidence of resistance
and in common with other antibiotics,
the concentration achieved after topical
application is so high it makes culture
and sensitivity relatively unhelpful. The
sensitivity of most bacteria is dose
dependant, and choice is best based on
clinical factors and cytology.
And then while EpiOtic is a
cleaner of choice, containing as it does
the antibacterial parachlorometaxylenol
(or PCMX as it’s too long a molecule
name to write let alone pronounce!), it
should not be used in cases of
tympanic membrane damage, whereas
chlorhexidine at a concentration of
less than 0.2% is safe.
Filippo is clearly a big fan of the
Virbac range, and one had to admit
that he had a point – it is the only
veterinary company committed to
producing a comprehensive range of
topical skin disease therapies. And
after his exhortations, they are
undoubtedly useful weapons in our
armoury.
