A-Textbook-of-Clinical-Pharmacology-and-Therapeutics-5th-edition

ADVERSE DRUG REACTIONS INVOLVING THE SKIN 417
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 treatment
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
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
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
of Sarcoptes 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)