White : Diseases of the Skin

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Gary M. White & Neil H. Cox

Diseases of the Skin

3	Topical Therapy

TOPICAL ANTIMIROBIAL AGENTS AND ANTIBIOTICS

Agents for acne and rosacea

Benzoyl peroxide

Benzoyl peroxide remains an excellent agent in the treatment of acne. Its ability to kill P. acnes is unsurpassed. Furthermore, bacterial resistance does not occur, in contrast to clindamycin and erythromycin. Washes are less effective compared with the usually recommended water-based gels. The 10% is only modestly more effective compared with the 5% and, given the higher concentration's tendency to cause excessive drying, the 5% is recommended. The patient should be warned that benzoyl peroxide can bleach carpet, sheets, and clothing. It is often best to apply at night with a topical retinoid (e.g. tazarotene 0.1% cream) in the morning.

Azelaic acid

This is only licensed for the treatment of acne in the UK , having antimicrobial and anticomedonal actions. However, it is also used more widely as a depigmenting agent in some countries, particularly for disorders such as melasma.

Topical antibiotics for acne

Both clindamycin and erythromycin are given b.i.d. to reduce the numbers of P. acnes in patients with acne. Unfortunately, bacterial resistance is common. Combinations of either one of these agents with benzoyl peroxide are available and should decrease the potential problem of resistance. In the UK , erythromycin is also combined with zinc for topical use in acne. Topical tetracycline is less effective.

Although some of these topical antibiotics may help in rosacea, they are often in vehicles appropriate for greasy skin and may be irritant in the typically older age group in which rosacea is more common.

Metronidazole

Topical metronidazole is used in treatment of rosacea. Several vehicles are used, and patients may need to try different options to find the one that is most acceptable.

PRACTICE POINTS

•	Benzoyl peroxide is the most effective at reducing levels of the bacteria that causes acne, but be careful. It can bleach the carpets!
•	Topical tetracycline fluoresces under Wood's light or UV lights as often used at discos; it is useful to confirm compliance but appreciation of the social impact of this effect is quite variable.
•	If using a topical and a systemic antibiotic together, it is recommended to use the same agent.
•	Use of benzoyl peroxide with a topical antibiotic in acne decreases the risk of bacterial resistance.

Agents for skin infections

Many such treatments are discussed in relation to specific disorders in Chapters 24 – 27, and are therefore covered only briefly here.

Bacterial infection

Several antibiotics are available topically, including the following.

•	Aminoglycosides and polymyxins (e.g. neomycin). Often used for otitis and some wounds, but contact sensitivity is relatively frequent.
•	Mupirocin—mainly used for staphylococcal infection, but increasingly being reserved for infections due to methicillin-resistant Staphylococcus aureus (MRSA)
•	Silver sulfadiazine—especially used for burns.
•	Fusidic acid—used for staphylococcal infection, and available in some countries as a combination product with steroids for infected eczema, but increasing bacterial resistance problems mean that use should be limited to short courses. An oral antibiotic is preferred for widespread impetigo or infected eczema.
•	Metronidazole—mainly used for malodorous wounds, ulcers, or ulcerated tumors.
•	Antiseptics—these have a wider spectrum of activity than that of antibiotics; many are used topically, such as povidone–iodine, chlorhexidine, etc.

Fungal infection

Agents available to treat fungal infections include the following.

•	imidazoles—several are available (e.g. ketoconazole); they can treat yeasts or dermatophytes.
•	allylamines (e.g. terbinafine)—they can treat yeasts or dermatophytes when used topically, and are fungicidal.
•	Nystatin (a polyene)—usually reserved for the treatment of Candida infection
•	Amorolfine (a morpholine)—used topically for nail dermatophyte infection, but benefit is usually limited to distal infection of relatively non-thickened nails; it is useful for superficial white onychomycosis (Ch. 26) and has activity against some moulds.
•	Ciclopirox olamine is available in the USA but not in the UK ; it has a broad spectrum of action and is available in several formulations.
•	Undecylenic acid—of notably lower potency.

Virtually all prescription topical antifungal agents are sufficient to treat simple dermatophytosis. Of the over-the-counter agents, terbinafine has the advantage of a fungicidal activity, whereas the imidazoles are fungistatic and usually less rapid in achieving benefit.

Topical imidazoles are also of value in seborrheic dermatitis (where they are sometimes used as combination products with hydrocortisone) and in treatment of pityriasis capitis and pityriasis versicolor; see also this chapter's section on shampoos.

Viral infection

Topical aciclovir and related agents such as penciclovir are available for herpes simplex infection, often by direct sale to the public and with limited efficacy.

Treatments for warts are discussed later, as they are largely not actually specifically antiviral.

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