Metronidazole allergic reaction
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Metronidazole Allergic Reactions: An Overview
Introduction to Metronidazole Allergy
Metronidazole, a 5-nitroimidazole compound, is commonly used to treat various infections, including those caused by Trichomonas vaginalis. Despite its widespread use and general tolerance, allergic reactions to metronidazole can occur, manifesting in various forms ranging from mild skin reactions to more severe systemic responses .
Types of Hypersensitivity Reactions
Immediate Hypersensitivity Reactions
Immediate hypersensitivity reactions to metronidazole are rare but can be severe. These reactions typically occur within minutes to hours after drug administration and are mediated by IgE antibodies. Symptoms may include pruritus, erythema, urticaria, shortness of breath, and dizziness, as observed in a 69-year-old patient who experienced these symptoms shortly after receiving metronidazole intravenously. Another case reported an 83-year-old female developing vomiting immediately after ciprofloxacin administration, indicating an IgE-mediated anaphylactic reaction.
Delayed Hypersensitivity Reactions
Delayed hypersensitivity reactions, or Type IV reactions, occur hours to days after exposure to the allergen. These reactions are T-cell mediated and can present as maculopapular rashes, itching, and erythema. For instance, a patient developed a widespread erythematous maculopapular rash and labial angioedema 10 hours after taking oral metronidazole. Another case involved a patient developing facial dermatitis with erythema, swelling, and itching after using topical metronidazole cream for acne rosacea.
Allergic Contact Dermatitis
Allergic contact dermatitis (ACD) is a common manifestation of metronidazole allergy, particularly with topical formulations. A 68-year-old woman developed ACD to metronidazole gel, confirmed by positive patch tests. Similarly, a 40-year-old woman with no prior history of allergies developed facial dermatitis after using metronidazole cream, with diagnostic patch testing confirming the allergy.
Cross-Reactivity Concerns
Cross-reactivity between metronidazole and other compounds, such as isothiazolinones, has been suggested. This is based on the structural similarities between these molecules, which may lead to cross-sensitization. For example, a patient allergic to both metronidazole and isothiazolinones reacted to metronidazole gel after a short incubation period, indicating possible cross-reactivity .
Diagnostic and Management Strategies
Skin Testing
Skin prick tests (SPTs) and patch tests are valuable tools for diagnosing metronidazole allergy. In one case, patch tests with metronidazole showed positive reactions, while SPTs were negative, highlighting the importance of using both tests for accurate diagnosis.
Avoidance and Alternative Treatments
Once a metronidazole allergy is confirmed, it is crucial to avoid the drug in any form. Patients should inform healthcare providers of their allergy to prevent future exposure. Alternative treatments, such as systemic erythromycin for rosacea, can be effective substitutes.
Conclusion
Metronidazole allergic reactions, though uncommon, can range from mild skin reactions to severe systemic responses. Immediate and delayed hypersensitivity reactions, as well as allergic contact dermatitis, are the primary manifestations. Cross-reactivity with other compounds like isothiazolinones may occur, necessitating thorough diagnostic testing. Proper identification and avoidance of metronidazole are essential for managing these allergies effectively.
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