A man who had suffered a minor dog bite (left) presented to the emergency department, where the wound was cleaned with an iodine solution and pressure-irrigated with saline. Rabies was not considered a significant possibility, but amoxicillin/clavulanate was prescribed to protect against the bacteria typically transmitted by a dog bite. When the patient returned for follow-up three days later, however, he thought that the bite had become infected despite the antibiotics. The skin was irritated, indurated, pruritic, and peppered with small blisters. Pain and soft-tissue swelling were insignificant, with no pus, lymphangitis, or fever detected. The treating physician considered changing the antibiotics and possibly admitting the patient for more extensive wound care.
     In a related case, a woman fell on cement and sustained a superficial abrasion (right). She cleaned it with soap and water and applied an over-the-counter antibiotic ointment. When the wound became irritated and mildly edematous over the following three days, she went to the emergency department to request an antibiotic for an apparent infection.
     Why were the wounds of these two patients failing to heal properly?

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ANSWER

Although infection might be the first complication to come to mind, both wounds demonstrate the characteristic appearance of allergic contact dermatitis. In each case the irritation was caused by use of a nonprescription antibiotic ointment containing neomycin.
    When wound healing appears to be delayed or new symptoms develop, the clinician usually suspects a retained foreign body or an infection, but an allergic contact dermatitis may also be the cause. Many patients routinely apply antiseptic solutions or other topical preparations to minor skin irritations or injuries and neglect to inform their physicians about these home treatments when the wound does not heal as anticipated. A careful history is necessary to elicit any potential allergens that might have been applied. Once the cause is identified and removed, the problem will quickly resolve.
     Over-the-counter products are usually well tolerated, but many topical medical interventions, including adhesive tape and even corticosteroid preparations, have the potential to produce an allergic reaction. Neomycin is a well-known topical sensitizer, and this adverse effect has curtailed the use of prescription-strength ear and eye drops containing the antibiotic. Neomycin-based ointments, of course, are readily available over the counter.
 

Emerg Med 34(11):51, 2002

Dr. Roberts is professor of emergency medicine at the Medical College of Pennsylvania and chairman of the department of emergency medicine at Mercy Catholic Medical Center in Philadelphia. He is also a member of the Emergency Medicine editorial board.