What Are the Signs of a Neomycin Allergy?

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  • Written By: Rebecca Harkin
  • Edited By: Melissa Wiley
  • Last Modified Date: 15 September 2019
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Often used as a topical ointment to prevent infection, neomycin may cause an allergic reaction, the most common sign of which is an itchy, red rash that may progress to blisters if use of the ointment is not discontinued. Signs of an allergic reaction to oral neomycin, used to treat an imbalance of intestinal flora, are facial swelling, hives, and sluggish respiration. A suspected allergy to neomycin is investigated using a patch test or intradermal test.

Typically, neomycin is used as a topical antibiotic. As a result, contact dermatitis is the most common first sign of an allergy to neomycin. Contact dermatitis is characterized by a red, raised rash and itchiness at the application sight. More severe reactions, such as burn-like wounds or blisters, may develop if use of the neomycin cream is not stopped.

Symptoms of an oral neomycin allergy are quite different from the topical neomycin allergy. An allergy to oral neomycin usually begins with swelling of the mouth, tongue, or throat. Hives will also accompany this reaction. Some patients also experience a shortness of breath or heaviness in the lungs. Medical help should be sought immediately if any of these symptoms are observed.


When a neomycin allergy is suspected, a patch test may be ordered by the patient’s doctor. A patch test evaluates an allergy by applying a low dose of this antibiotic to the skin. If a rash develops at the site of the patch test, the neomycin allergy is confirmed. When a rash is not observed, a more sensitive intradermal test may be ordered. In an intradermal test, an injection of neomycin, made just under the skin, is observed for signs of an allergic reaction, such as hives or redness.

Once an allergy to an antibiotic has been discovered, the patient needs to be aware of the uses of this antibiotic and products that may contain neomycin and should inform all of his doctors of his neomycin allergy. Neomycin can be found in antibiotic creams and lotions, antibiotic eye drops, and in some oral medications used to treat harmful intestinal bacteria. This antibiotic may also be used as a preservative in some vaccines. This type of antibiotic is sometimes added to cosmetics, deodorants, and soaps to extend the shelf life of these products. Antibiotics such as neomyci, may also be added to pet food and some veterinary supplies.

The side effects of neomycin are most often related to the topical ointment. These side effects include a burning sensation or redness. When this occurs, use of the cream should be discontinued and the prescribing physician should be consulted. If use continues, a rash may develop that is itchy and uncomfortable. In rare cases, usually with long-term use, a patient may have difficulty urinating or develop problems hearing.


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