A Textbook of Clinical Pharmacology and Therapeutics

TREATMENT OF OTHER SKIN INFECTIONS

(LICE, SCABIES)

The treatment of lice and scabies is covered in Table 51.5.

ADVERSE DRUG REACTIONS INVOLVING

THE SKIN

Cutaneous adverse drug reactions can arise from topically or
systemically administered drugs. The clinical presentation of
an adverse cutaneous drug reaction is seldom pathognomonic
and may vary from an erythematous, macular or morbilliform
rash to erythema multiforme. Such reactions generally occur
within the first one or two weeks of therapy. However,
immunologically mediated reactions may take months to
become clinically manifest. Contact dermatitis is usually

eczematous and is most commonly seen with antimicrobial

drugs or antihistamines. Sometimes the vehicle is the culprit.

The diagnosis of a drug-induced cutaneous reaction requires

an accurate drug history from the patient, especially defining

the temporal relationship of the skin disorder to concomitant

drug therapy. In milder cases and fixed drug eruptions,

re-administration (rechallenge) with the suspect agent may be

justified. Patch testing is useful for contact dermatitis. The treat-

ment of drug-induced skin disorders involves removing the

cause, applying cooling creams and antipruritics, and reserving

topical steroids only for severe cases.

Table 51.6 lists some of the most common drug-related

cutaneous reactions.

PHOTOSENSITIVITY

The term ‘photosensitivity’ combines both phototoxicity and

photoallergy. Phototoxicity (like drug toxicity) is a predictable

ADVERSEDRUGREACTIONSINVOLVING THESKIN 417

Table 51.5:Summary of the treatments for other common dermatological infections

Disease Causal agent Treatment Toxicity of therapy Additional comments

Lice Caused by Pediculus 0.5% malathion or carbamyl Use aqueous rather than Apply to affected area and

humanus capitis are recommended – leave alcohol preparations in repeat in 7 days to kill lice

in contact for 12 h asthmatics and small children that have just emerged from

eggs

Scabies Caused by transmission Lindane 1% (apply Major toxicity is skin Do not use lindane or

ofSarcoptes scabei topically and leave for 24 h, irritation malathion during pregnancy

then repeat after 7 days if or in children. Permethrin is

needed) or malathion 0.5% an effective alternative

applied to hair and left for pyrethroid

12 h (if on whole body

leave for 24 h)

Table 51.4:Summary of drug therapy of viral skin infections

Viral skin infection Drug therapy Comment

Initial or recurrent genital Topical 5% aciclovir cream, Topical penciclovir (2% cream) is an

labial or herpes simplex 4-hourly for 5 days is used, but is of alternative for recurrent orolabial

questionable benefit. Systemic herpes. Systemic valaciclovir or

aciclovir therapy is required for famciclovir are new alternatives to

buccal and vaginal herpes simplex aciclovir

Skin warts, papilloma All treatments are destructive. For plantar warts use 1.5%

virus infections Cryotherapy (solid carbon dioxide, formaldehyde or 10% glutaraldehyde.

liquid nitrogen). Daily keratolytics, For anal warts use podophyllin resin

such as 12% salicylic acid 15% or podophyllotoxin 0.5% solution

applied precisely on the lesions once or

twice weekly