Answer:
Topical antibiotics are the single most important factor in minimizing septic complications. No perfect topical antibiotic exists.
The goals for therapy are to:
1. Delay colonization of the wound.
2. Keep the wound bacterial density lower than would otherwise occur.
3. Keep the wound flora more homogeneous and less diverse than without therapy.
Silver sulfadiazine: the most frequently used topical agent. It was introduced in the early 1970's by Fox. It is supplied in a water-soluble base at a concentration of 1%. This concentration is sufficient to inhibit growth of most sensitive microorganisms in vitro. It is generally applied every 12–24 hours and can be used with or without dressings. It is active in vitro against a number of gram positive and gram negative bacteria. Candida albicans, and perhaps herpes viruses. It is not clear whether its antibacterial effect is from the parent compound, the silver ion, or the sulfadiazene moiety. Minimal pain is associated with its application and it is nonstaining. Its wound penetration is intermediate between the rapidly-absorbed mafenide and the poorly absorbed silver nitrate. Systemic absorption does occur, but documented episodes of toxicity have been quite rare. Leukopenia is not infrequently seen after 2–3 days of treatment with this agent. It usually resolves without discontinuing the drug. Leukopenia rarely depresses the white count to <2,000 white blood cells/mm3.
Silver nitrate (0.5% solution): Silver nitrate solution is not toxic in a 0.5% concentration, but it has a significant antimicrobial effect. It was introduced in 1965 by Moyer. It is a broad-spectrum agent; development of resistance to the silver ion is distinctly uncommon. There is minimal absorption from the burn wound, making toxicity virtually unknown. Because of its minimal absorption, it is an excellent prophylactic agent, but it is not indicated for established wound sepsis. The solubility properties of silver nitrate mandate preparation in distilled water; therefore, a 0.5% solution is markedly hypotonic. Its use can lead to substantial leaching of sodium, potassium, and other plasma solutes from the burn wound. Careful monitoring of serum electrolytes is mandatory.
Silver nitrate solution must be used by soaking bulky wet dressings. These must be kept wet every two hours to keep the concentration of the agent at <2%, which is caustic and cytotoxic. Silver nitrate stains everything it touches brown or black. Removal of these stains from linen markedly shortens the life of the linen. It is not painful upon application.
Mafenide: Mafenide is usually applied every 12 hours. It has a broad antibacterial spectrum; its mechanism of action is unknown. It has the best eschar penetration of any agent, and it also efficiently penetrates cartilage. This makes it an excellent choice for use on burned ears and noses. With its active penetration, after three hours little agent is left on the wound surface; thus BID administration is necessary. Mafenide is a strong carbonic anhydrase inhibitor and its use results in an alkaline diuresis. It can lead to acid-base abnormalities when used on >20% of the body surface area. The polyuria induced by the agent can lead to a hyperchloremic metabolic acidosis, which, if then compensated for by hyperventilation, may eventually lead to pulmonary failure in the compromised patient. Significant pain results from the application of mafenide, probably due to its high osmolarity.