A new topical antibiotic, retapamulin 1% ointment (Altabax), has recently been approved for the treatment of impetigo in adults and children. The drug is the first in a new class of antibiotics called pleuromutilins, which are produced by fungi and work by binding to a unique site of the ribosome, part of the internal workings of a bacterial cell.

Retapamulin is indicated for the treatment of localized impetigo caused by susceptible strains of Staphylococcus aureus or Streptococcus pyogenes. S aureus is responsible for about 75% to 80% of impetigo cases, and the remainder is caused by S pyogenes (group A beta-hemolytic streptococcus).

Until now, mupirocin 2% ointment (Bactroban, Centany) was the mainstay of topical therapy, but the introduction of this new antibiotic class offers new treatment options, especially in the face of increasing treatment resistance.

Unlike mupirocin, which must be applied 3 or 4 times a day for up to 12 days, retapamulin is applied only twice a day for 5 days.

The Changing Face of Impetigo

Impetigo, a very contagious infection of the superficial skin, is the most common bacterial skin infection in children but can occur at any age. As with other types of skin infections, the elderly are more susceptible than younger adults to becoming infected with impetigo. Adult patients tend to present days, or even weeks, after the development of pruritic vesicular lesions, which are formed at the site of a minor trauma to the skin.

Impetigo begins with a big bullous lesion, but physicians rarely see that stage, since patients normally present after the bullous has popped, when they have honey-colored crusted, or red and weeping-like lesions (Figure). Lately, a lot of impetigo looks like an eczema-type rash.

Figure—Impetigo in a 25-year-old man.

In fact, eczema may be a common precipitant of impetigo. It can be hard to distinguish whether the eczema is just getting redder, or if it is infection. If treated with topical steroids or topical antiinflammatory creams, and no response is seen after a few days, this is an indication of secondary infection, which likely suggests an impetigous-type infection.

Prescribing Retapamulin

Retapamulin should be used only for localized impetigo, covering up to 100 cm² in total area in adults or up to 2% of the total body surface area in children.

In clinical studies, retapamulin was very effective against S aureus and S pyogenes, including strains resistant to existing antimicrobial agents. Clinical success rates were significantly better with retapamulin than with placebo (See Table).

Click image for larger version.

A 56.7% difference in clinical success rate was seen compared with placebo among patients who had S aureus strains that were resistant to fusidic acid (a topical antibacterial agent not available in the United States) at baseline.

Retapamulin is considered safe and effective for the treatment of elderly patients, based on clinical trials that included 234 patients aged 65 years or older.

To prevent the development of drug resistance and to maintain the efficacy of retapamulin and other antibacterial agents, its use should be confined to the treatment or prevention of infections that are proven by culture or strongly suspected of being caused by susceptible bacteria.

Patients should be instructed to apply a thin layer of retapamulin to the affected area twice daily for 5 days. Although the treated area does not need to be covered, patients may use a sterile bandage or gauze dressing.

Because of the limited systemic exposure after topical application, dose adjustments are unnecessary when coadministered with cytochrome (CY) P 450-3A4 inhibitors, such as ketoconazole (Nizoral). Retapamulin should have little effect on the metabolism of other CYP450 substrates.

Current guidelines cite mupirocin as the best available topical therapy, but these were composed before the approval of this new class of antibiotics. Moreover, resistance to mupirocin is increasing, with a reported prevalence ranging from 5% to 15%. And although not enough data are yet available to claim that retapamulin will work in mupirocin-resistant impetigo, experts think it might do so at least for some time to come.