...greater in treating impetigo and skin infections. Awareness of all these agents provides a dermatologist additional tools with which to treat skin infections. As a wide variety of topical antibiotics, combination antibiotics, and combination anti-inflammatory preparations used by ophthalmologists are not part of the therapeutic armamentarium of most dermatologists, this review will provide the knowledge needed to rationally use such ophthalmologic preparations. Finally, information related to the topical nadifloxacin for acne and skin infections, which is in clinical use in Japan, is summarized.

Introduction

Skin infections are a common reason for patients to seek attention from dermatologists. This review seeks to survey topical antibiotics that might be useful for a dermatologist. The most common causes of skin infection are the gram-positive pathogens Staphylococcus aureus (eg, carbuncles, folliculitis impetigo, scalded skin syndrome) (1) and Streptococcus pyogenes (eg, erysipelas, cellulitis). (1) Other rarer causes of skin infections include Pseudomonas aeruginosa (eg, otis externa, hot tub folliculitis, and ecthyma gangrenosum), (2) Corynebacterium (eg, ulcers, (3) erythrasma, trichomycosis axillaris, and pitted keratolysis (4)), Erysipelothrix insidiosa, (eg, erysipeloid), and Haemophilus influenzae (eg, facial cellulitis in children). (5)

Most topical antibiotics are directed against S aureus and S pyogenes. (6-10) Acne is related to the presence of Propionibacterium acnes in a complex fashion, which is not related strictly to infection. There are also a variety of antibiotics that are used in the setting of burn care that cover for gram-positive and gram-negative pathogens.

Topical antibiotics available to dermatologists are summarized in Table 1. (11) A brief review of the mechanisms of these topical antibiotics is provided and is useful in understanding how and where to use a topical antibiotic. (12-17) These antibiotics are broken down into 5 classes: (1) cell wall synthesis inhibitors; (2) ribosome function inhibitors; (3) sulfur drugs; (4) antibiotic burn treatment agents; and (5) miscellaneous agents. (6-11)

Topical Antibiotics

Cell Wall Synthesis Inhibitors

The primary agents used for the treatment of impetigo and skin infections are inhibitors of cell wall synthesis (ie, mupirocin bacitracin, polymyxin B, and gramicidin). (6-10) These agents are bactericidal and kill bacteria not actively dividing. (6-10)

Mupirocin (pseudomonic acid A) blocks protein synthesis in bacteria by inhibiting bacterial isoleucyl-tRNA synthetase. (18) Mupirocin is effective against gram-positive bacteria, but not against gram-negative bacteria. (19) Mupirocin is marketed as a cream and ointment in the US, the European Union, and Japan for the treatment of impetigo. (6-10) An intranasal form was approved in 1995 and is effective at eradicating nasal carriage of S aureus, but now has limited commercial availability in the US. (20)

Polymyxin B is an antibiotic primarily used for resistant gram-negative infections. It is a common component of topical antibiotics and is also available for oral use in severely ill patients with treatment-resistant pathogens. Polymyxin B interacts with phospholipid components of the bacterial cell membrane, increasing cell wall permeability. (21) These effects have a variety of mechanisms that include the: (1) alteration of cytoplasmic membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer, which has an electrostatic attraction for the positively charged amino groups in the cyclic peptide portion; (2) dissolution of the fatty acid portion in hydrophobic region of membrane and disrupts membrane integrity; (3) inactivation by binding endotoxin; and (4) inhibition of cellular respiration. (21)

Bacitracin and gramicidin interfere with bacterial cell wall synthesis by inhibiting the regeneration of phospholipid receptors involved with peptidoglycan synthesis. (22) Bacitracin combined with polymyxin B and neomycin is available as Neosporin[R] ointment, also called a triple antibiotic. (23) In the Neosporin solution formulation, gramicidin replaces bacitracin, since bacitracin is unstable in water. (24) In terms of activity, gramicidin is almost identical to bacitracin, but more water soluble.

Ribosome Function Inhibitors

Ribosome function inhibitors possess a wider spectrum of antibacterial activity, possessing activity against gram-positive pathogens, like S aureus and S pyogenes, and gram-negative pathogens. These agents...

NOTE: All illustrations and photos have been removed from this article.



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