Lecture Notes Dermatology - Graham-Brown, Robin, Burns, Tony

22
Treatment of s kin d isease
If it ’ s dry, wet it. If it ’ s wet, dry it. Congratulations,
you are now a dermatologist!
Anonymous
The above witticism is oft quoted by non -
dermatologists as an assessment of the scope of
dermatological therapeutics. An alternative calumny
relates to a dermatologist murmuring an
unintelligible Latin name as a diagnosis and then
prescribing a topical steroid, for everything. Apart
from being deeply offensive to sensitive skin
doctors, both these quips are far from the truth, as
dermatologists have an enormous therapeutic
armamentarium at their disposal. In days of yore,
it must be admitted, many of the available topical
therapies resembled witches ’ brews containing
‘ Eye of newt and toe of frog, wool of bat and
tongue of dog ’ . They were often cosmetically
unacceptable and malodorous — if the skin disease
did not render the patient a social pariah, the
treatment could be relied upon to do so. However,
in recent years, topical therapies have not only
become more effective, but also cosmetically
much more acceptable.
The treatment of individual disorders has been
dealt with in preceding chapters, and this chapter
is designed to provide an overview of the principles
of therapy.
penetrate well, but remain localized within the
skin, thereby avoiding potential problems from
systemic effects. In practice this is extremely difficult
to achieve, and any agent that penetrates the
stratum corneum is absorbed to some extent.
Topical preparations consist of an active ingredient
(or ingredients) and a material in which this
is suspended — a base. These components must be
compatible. There is little point in discovering a
new base that penetrates the skin like a hot knife
through butter if it completely inactivates everything
suspended in it.
The stratum corneum forms a natural protective
barrier to penetration of externally applied
agents. Hence, to facilitate penetration by a drug,
this barrier function must be breached, and this
can be achieved by hydration of the stratum
corneum, e.g. penetration of a topical steroid may
be markedly enhanced by occluding an area of
skin with polythene. Unfortunately, if large areas
of skin are occluded in this way the amount of
steroid absorbed may be sufficient to produce systemic
effects. Bases containing urea also hydrate
the stratum corneum and enhance penetration of
their active ingredients. Dimethyl sulfoxide
(DMSO) is a solvent that penetrates skin extremely
rapidly, and is used as a vehicle for the antiviral
agent idoxuridine.
Topical t herapy
With regard to topical therapy, an ideal preparation
for the management of skin disease would
Lecture Notes: Dermatology, 10th edition. © RAC Graham-Brown
and DA Burns. Published 2011 by Blackwell Publishing Ltd.
Bases
Bases include creams, oily creams, ointments,
lotions, gels and pastes. A cream is an oil - in -
water emulsion that is relatively non - greasy and
has only limited emollient activity. Creams are