A Textbook of Clinical Pharmacology and Therapeutics

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

Acitretinis the active carboxylated metabolite of etretinate. It
is given orally for the treatment of severe resistant or compli-
cated 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.
Acitretinis well absorbed. Unlike its parent compound,
etretinate,acetretinis not highly bound to adipose tissue. Its
eliminationt1/2is shorter than that of the parent drug, but
even so pregnancy must be avoided for two years after stop-
ping treatment. Hepatic metabolism is the major route of
elimination.
Acitretinis 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 tetracyclineincreases the risk
  of raised intracranial pressure.
  
  
  • Hypertriglyceridaemia: other drugs (e.g. vitamin D
    analogues) can have additive effects.
  
  
  • It increases methotrexateplasma 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 strepto-

cocci. 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

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.

416 DRUGS AND THE SKIN

Table 51.3:Drug therapy of fungal skin and nail infections

Fungal skin infection Drug therapy Comment

Candidainfection 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%, topical ketoconazole 2% or clotrimazole 1%

with cetrimide shampoo

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% refractory cases

applied for 2–3 weeks

Tinea pedis As for tinea corporis As for tinea corporis