Clinical Review

Patch Testing for Adverse Drug Reactions

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Systemic Contact Dermatitis

Drugs historically recognized as causing allergic contact dermatitis (eg, topical gentamycin) can cause systemic contact dermatitis, which can be patch tested. In these situations, systemic contact dermatitis may be due to either the active drug or excipients in the medication formulation. Excipients are inactive ingredients in medications that provide a suitable consistency, appearance, or form. Often overlooked as culprits of drug hypersensitivity because they are theoretically inert, excipients are increasingly implicated in drug allergy. Swerlick and Campbell63 described 11 cases in which chronic unexplained pruritus responded to medication changes to avoid coloring agents. The most common culprits were FD&C Blue No. 1 and FD&C Blue No. 2. Patch testing for allergies to dyes can be clinically useful, though a lack of commercially available patch tests makes diagnosis difficult.64

Other excipients can cause cutaneous reactions. Propylene glycol, commonly implicated in allergic contact dermatitis, also can cause cutaneous eruptions upon systemic exposure.65 Corticosteroid-induced systemic contact dermatitis has been reported, though it is less prevalent than allergic contact dermatitis.66 These reactions usually are due to nonmethylated and nonhalogenated corticosteroids including budesonide, cortisone, hydrocortisone, prednisolone, and methylprednisolone.67,68 Patch testing in these situations is complicated by the possibility of false-negative results due to the anti-inflammatory effects of the corticosteroids. Therefore, patch testing should be performed using standardized and not treatment concentrations.

In our clinic, we have anecdotally observed several patients with chronic dermatitis and suspected NSAID allergies have positive patch test results with propylene glycol and not the suspected drug. Excipients encountered in multiple drugs and foods are more likely to present as chronic dermatitis, while active drug ingredients started in hospital settings more often present as acute dermatitis.

Our Experience

We have patch tested a handful of patients with suspected drug eruptions (University Hospitals Cleveland Medical Center institutional review board #07-12-27). Medications, excipients, and their concentrations (in % weight per weight) and vehicles that were tested include ibuprofen (10% petrolatum), aspirin (10% petrolatum), hydrochlorothiazide (10% petrolatum), captopril (5% petrolatum), and propylene glycol (30% water or 5% petrolatum). Patch tests were read at 48 and 72 hours and scored according to the International Contact Dermatitis Research Group patch test scoring guidelines.69 Two patients tested for ibuprofen reacted positively only to propylene glycol; the 3 other patients did not react to aspirin, hydrochlorothiazide, and captopril. Overall, we observed no positive patch tests to medications and 2 positive tests to propylene glycol in 5 patients tested (unpublished data).

Areas of Uncertainty

Although tests for immediate-type hypersensitivity reactions to drugs exist as skin prick tests, diagnostic testing for the majority of drug reactions does not exist. Drug allergy diagnosis is made with history and temporality, potentially resulting in unnecessary avoidance of helpful medications. Ideal patch test concentrations and vehicles as well as the sensitivity and specificity of these tests are unknown.

Guidelines From Professional Societies

Drug allergy testing guidelines are available from the British Society for Allergy and Clinical Immunology70 and American Academy of Allergy, Asthma and Immunology.71 The guidelines recommend diagnosis by history and temporality, and it is stated that patch testing is potentially useful in maculopapular rashes, AGEP, fixed drug eruptions, and DRESS syndrome.

Conclusion

Case reports in the literature suggest the utility of patch testing in some drug allergies. We suggest testing excipients such as propylene glycol and benzoic acid to rule out systemic contact dermatitis when patch testing with active drugs to confirm cause of suspected adverse cutaneous reactions to medications.

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