Be alert for possible allergic contact dermatitis from certain topical meds

Allergic contact dermatitis caused by topical medications is a common and under-recognized condition. It's considered a type IV delayed hypersensitivity reaction that requires a previous episode of sensitization. Allergic contact dermatitis can occur with even a single topical application and therefore may not always be evident when taking a patient history. Sensitization usually takes at least two weeks to develop. Symptoms Symptoms of acute allergic contact dermatitis may include vesicles, crusting and weeping. Chronic cases often are typified by scaly or lichenified papules and plaques. These skin changes often appear in a well-delineated area where contact with the allergen occurred. However, they can become more generalized and affect non-exposed sites. Diagnosis A complete drug history is helpful when a patient’s skin condition is suspected to be caused by a topical medication. Patch testing is indicated for anyone with suspected allergic contact dermatitis to topical medications and can help guide patient counselling regarding allergen avoidance. Causative agents Topical antibiotics, anesthetics, corticosteroids and propylene glycol (present in the vehicle of many topical medicaments) are most commonly associated with allergic contact dermatitis from topical medications. The topical antibiotics most commonly implicated are bacitracin and neomycin, followed by polymyxin B, including these antibiotics found in OTC topical products. Allergic contact dermatitis due to topical antibiotics often involves the use of topical antibiotics following surgical procedures, where the developing dermatitis might be mistaken for infection. Petrolatum or other bland emollients are recommended instead of topical antibiotic products for postoperative wound care; they have a comparable low infection rate, without the risk of inducing allergic reactions. Allergic contact dermatitis to topical corticosteroids can be challenging to diagnose. Patients might be allergic to the corticosteroid itself or to an excipient (e.g., propylene glycol). Patients often have a history of atopic dermatitis, which might coexist with allergic contact dermatitis. Corticosteroid allergy is often not considered, as these medications are often the treatment of choice for eczematous dermatitis. Ongoing use might lead to further worsening of the patient’s dermatitis. Healthcare providers should consider allergic contact dermatitis in patients with corticosteroid-sensitive skin disease that does not respond (or worsens) with appropriate corticosteroid treatment. Corticosteroids can be classified into three groups based on their chemical structure and reaction patterns. If an allergy is identified (by patch testing) within one group, a corticosteroid from another group can usually be used safely. Cross-reactivity between groups is very rare and most allergies are to corticosteroids in group 1 (hydrocortisone type). Topical anesthetics are found in a variety of prescription and OTC products. Lidocaine is the most common culprit, followed by benzocaine. Although patch testing can confirm a contact allergy to topical anesthetics applied directly to the skin, patients will not necessarily develop an allergic reaction to the same anesthetic injected into the dermis or subcutaneously (e.g., for dermatologic and dental procedures). Propylene glycol is an excipient in many topical medications, cosmetics, soaps and sunscreens. A large percentage of patients with propylene glycol allergy have a history of atopic dermatitis. This might be related to the presence of propylene glycol in topical eczema treatments (e.g., moisturizers, topical corticosteroids, pimecrolimus cream, crisaborole ointment). Allergic contact dermatitis to propylene glycol should be suspected in patients with eczematous eruptions that do not respond appropriately to treatment with topical corticosteroids or anti-inflammatory drugs that contain propylene glycol. In patients with patch-testing confirmed allergy who require topical anti-inflammatory drugs, a few propylene glycol-free topical corticosteroids are available, as well as tacrolimus ointment. Summary Allergic contact dermatitis is often an overlooked diagnosis, but should be part of the differential diagnosis for any pruritic eczematous eruption. Reference 1. Choi C, Vafaei-Nodeh S, Phillips J, et al. Approach to allergic contact dermatitis caused by topical medicaments. Can Fam Physician 2021;67:414-9. https://www.cfp.ca/content/cfp/67/6/414.full.pdf (accessed June 22, 2021).

Be alert for possible allergic contact dermatitis from certain topical meds

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