A Textbook of Clinical Pharmacology and Therapeutics

● Introduction 411
● Acne 411
● Alopecia and hirsutism 412
● Dermatitis (eczema) 413
● Psoriasis 414
● Urticaria 416
INTRODUCTION
CHAPTER 51
DRUGS AND THE SKIN
Skin conditions account for up to 2% of consultations in general
practice. The ability of the practitioner to make a correct diagnosis
is paramount, and is aided by the ease of biopsy of the abnormal
tissue. The non-specific use of drugs which can modify the
appearance of skin lesions (e.g. potent topical glucocorticosteroids)
should be avoided in the absence of a diagnosis.
Adverse reactions to topical or systemic drugs produce a wide
variety of skin lesions. Drugs applied topically to the skin may
act locally and/or enter the systemic circulation and produce
either a harmful or beneficial systemic pharmacological effect.
Further details of transdermal drug absorption/delivery are
discussed in Chapter 4.
ACNE
Incidence and pathophysiology
Acne vulgaris is one of the most common skin disorders,
occurring in 80–90% of adolescents. It is associated with
Propionibacterium acnes infection of the sebaceous glands and
causes inflammatory papules, pustules, nodules, cysts and
scarring, mainly on the face, chest, back and arms.
PRINCIPLES OF TREATMENT
An algorithm for treatment of acne is outlined in Figure 51.1.
The topical use of keratolytic (peeling) agents, such as benzoyl
peroxide or retinoic acid (tretinoin) on a regular basis in conjunction
with systemic antibiotic therapy is successful in most
cases. The main side effect of keratolytic agents is skin irritation.
Azelaic acid is a natural product of Pityrosporum ovale, and has
both antibacterial and anti-keratinizing activity. It is less irritant
than benzoyl peroxide and preferred by some patients for this
● Superficial bacterial skin infections 416
● Fungal skin and nail infections 416
● Viral skin infections 416
● Treatment of other skin infections (lice, scabies) 417
● Adverse drug reactions involving the skin 417
reason, especially for facial lesions. Because of the powerful teratogenic
effects of oral vitamin A analogues, there has been concern
about the safety of topical retinoic acid derivatives in the
first trimester of pregnancy. However, a large study from the
USA has shown that topical retinoic acid is not associated with
an increased risk of major congenital abnormalities. Suitable
antibiotic treatment includes low-dose doxycycline or erythromycin
given until improvement occurs, which may take several
months. Tetracyclines should not be used until the secondary
dentition is established (i.e. after the age of 12 years). Pseudomembranous
colitis has occurred in patients on long-term tetracyclines
for acne, as has the development of microbial resistance.
Topical antibiotic preparations (e.g. tetracycline or clindamycin)
are less effective than systemic therapy.
For patients with disease that is refractory to these therapies,
the use of either low-dose anti-androgens or isotretinoin
(see below) should be considered, but only under the supervision
of a consultant dermatologist.
HORMONAL THERAPY OF ACNE
Acne depends on the actions of androgens on the sebaceous
glands. Hormone manipulation is often successful in women
with acne that is refractory to antibiotics and is useful in
patients who require contraception, which is essential because
of the potential for feminizing a male fetus. Cyproterone
acetate is an anti-androgen with central and peripheral activity,
and is combined with low-dose oestrogen, ethinylestradiol.
Some women with hirsutism may also benefit because
hair growth is also androgen-dependent. Contraindications
include pregnancy and a predisposition to thrombosis.
RETINOID THERAPY IN ACNE
The management of severe acne has changed dramatically
with the advent of the synthetic vitamin A analogues.