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Published on: November 16, 2016
Co-existing sensitivity to metronidazole and isothiazolinone
1The Dermatology Unit, Kaplan Medical Center, Rechovot, Israel. wolf_r@netvision.il
Clinical and Experimental Dermatology
|September 3, 2003
Summary
A woman experienced allergic contact dermatitis to metronidazole gel, likely due to cross-reactivity with methylchloroisothiazolinone and methylisothiazolinone. This suggests metronidazole allergy may be more common than previously thought.
Area of Science:
- Dermatology
- Allergology
- Toxicology
Background:
- Topical metronidazole is frequently prescribed for various skin conditions.
- Allergic contact dermatitis (ACD) is a common adverse reaction to topical medications.
- Isothiazolinones (e.g., methylchloroisothiazolinone/methylisothiazolinone) are prevalent preservatives and frequent causes of ACD.
Observation:
- A 68-year-old female patient presented with ACD to topical metronidazole gel.
- Patch testing confirmed allergy to the metronidazole gel and the active ingredient, metronidazole.
- The patient also had a known allergy to methylchloroisothiazolinone/methylisothiazolinone (MC/MI).
Findings:
- The patient exhibited a rapid reaction to metronidazole gel (1-day incubation), suggesting pre-existing sensitization.
- Structural similarities between metronidazole and isothiazolinones support a plausible cross-reaction.
- Positive patch tests confirmed allergies to both metronidazole and MC/MI.
Implications:
- This case highlights a potential cross-reactivity between metronidazole and isothiazolinones.
- It suggests that metronidazole allergy might be underdiagnosed and potentially more prevalent than current literature indicates.
- Clinicians should consider isothiazolinone cross-reactivity in patients with suspected metronidazole allergy.
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