A Textbook of Clinical Pharmacology and Therapeutics

●Introduction 411

●Acne 411

●Alopecia and hirsutism 412

●Dermatitis (eczema) 413

●Psoriasis 414

●Urticaria 416

●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

CHAPTER 51

52 Drugs and the eye

INTRODUCTION

Skin conditions account for up to 2% of consultations in general
practice. The ability of the practitioner to make a correct diagno-
sis is paramount, and is aided by the ease of biopsy of the abnor-
mal tissue. The non-specific use of drugs which can modify the
appearance of skin lesions (e.g. potent topical glucocortico-
steroids) 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 acnesinfection 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
peroxideorretinoic acid(tretinoin) on a regular basis in con-
junction with systemic antibiotic therapy is successful in most
cases. The main side effect of keratolytic agents is skin irritation.
Azelaic acidis a natural product of Pityrosporum ovale, and has
both antibacterial and anti-keratinizing activity. It is less irritant
thanbenzoyl peroxideand preferred by some patients for this

reason, especially for facial lesions. Because of the powerful tera-

togenic effects of oral vitamin A analogues, there has been con-

cern 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 acidis not associated with

an increased risk of major congenital abnormalities. Suitable

antibiotic treatment includes low-dose doxycyclineorerythro-

mycingiven 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). Pseudo-

membranous colitishas occurred in patients on long-term tetra-

cyclines for acne, as has the development of microbial resistance.

Topical antibiotic preparations (e.g. tetracyclineorclindamycin)

are less effective than systemic therapy.

For patients with disease that is refractory to these thera-

pies, the use of either low-dose anti-androgens or isotretinoin

(see below) should be considered, but only under the supervi-

sion 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

acetateis an anti-androgen with central and peripheral activ-

ity, and is combined with low-dose oestrogen, ethinylestra-

diol. 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.