A Textbook of Clinical Pharmacology and Therapeutics

416 DRUGS AND THE SKIN
UVA light, notably optimization of the dose regimen, have
reduced the risk of carcinogenicity. Phototherapy combined
with coal tar, dithranol, vitamin D or vitamin D analogues
allows reduction of the cumulative dose of phototherapy
required to treat psoriasis.
ACITRETIN
Acitretin is the active carboxylated metabolite of etretinate. It
is given orally for the treatment of severe resistant or complicated
psoriasis and other disorders of keratinization. It should
only be given under hospital supervision. A therapeutic effect
occurs after two to four weeks, with maximal benefit after six
weeks. Because it is highly teratogenic, women must take
adequate contraceptive precautions for one month prior to
and during therapy and for two years after stopping the drug.
Retinoids bind to specific retinoic acid receptors (RARs) in
the nucleus. RARs have many actions, one of which is to
inhibit AP-1 (transcription factor) activity.
Acitretin is well absorbed. Unlike its parent compound,
etretinate, acetretin is not highly bound to adipose tissue. Its
elimination t1/2 is shorter than that of the parent drug, but
even so pregnancy must be avoided for two years after stopping
treatment. Hepatic metabolism is the major route of
elimination.
Acitretin is contraindicated in the presence of hepatic and
renal impairment. Other contraindications and adverse effects
are as for isotretinoin (see above).
Drug interactions
Drug interactions include the following:
• Concomitant therapy with tetracycline increases the risk
of raised intracranial pressure.
Table 51.3: Drug therapy of fungal skin and nail infections
• Hypertriglyceridaemia: other drugs (e.g. vitamin D
analogues) can have additive effects.
• It increases methotrexate plasma concentrations and the
risk of heptotoxicity.
• It possibly antagonizes the action of warfarin.
URTICARIA
Acute urticaria is usually due to a type-1 allergic reaction:
treatment is discussed in Chapter 50.
SUPERFICIAL BACTERIAL SKIN INFECTIONS
Skin infections are commonly due to staphylococci or streptococci.
Impetigo or infected eczema is treated topically for
no more than two weeks with antimicrobial agents, e.g.
mupirocin.
FUNGAL SKIN AND NAIL INFECTIONS
For a summary of the drug therapy of fungal skin and nail
infections see Table 51.3. Chapter 45 gives a more detailed
account of the clinical pharmacology of antifungal drugs.
VIRAL SKIN INFECTIONS
Fungal skin infection Drug therapy Comment
For a detailed account of the pharmacology of anti-viral
drugs see Chapter 45. Table 51.4 gives a summary of the drug
therapy of viral skin infections.
Candida infection of the skin, Topical antifungal therapy with nystatin Alternative topical agents are terbinafine
vulvovaginitis or balanitis cream (100 000 units/g) or ketoconazole 2%, 1% or amorolfine 0.25% creams. Systemic
clotrimazole 1% or miconazole 2% cream therapy may be necessary in refractory cases.
Consider underlying diabetes mellitus
Fungal nail infections, Griseofulvin, 10 mg/kg daily for If systemic therapy is not tolerated, tioconazole
onychomycosis dermatophytes 6–12 months, or alternatively fluconazole, 28% is applied daily for 6 months.Topical
200 mg daily for 6–12 months amorolfine 5% is an alternative
Pityriasis capitis, seborrhoeic Topical steroids – clobetasol propionate Severe cases may require additional
dermatitis (dandruff) 0.05%, or betamethasone valerate 0.1%,
with cetrimide shampoo
topical ketoconazole 2% or clotrimazole 1%
Tinea capitis Systemic therapy with fluconazole,
itraconazole, miconazole or clotrimazole
–
Tinea corporis Topical therapy with, for example, Systemic therapy is only necessary in
ketoconazole 2% or clotrimazole 1%
applied for 2–3 weeks
refractory cases
Tinea pedis As for tinea corporis As for tinea corporis