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An effective communicator...

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01 December 2010, at 12:00am

NICK TREMLETT reports on an enlightening refresher course on otitis externa in dogs and cats and topical therapy in veterinary dermatology

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.