| Summary: | Background: A fixed drug eruption is a type IV hypersensitivity reaction to a medication that characteristically re-emerges on the same site each time the specific drug is taken. Antimicrobials (including fixed dose combinations) are frequently implicated in fixed drug eruption while gliptins (as separate drugs or as combined preparations) on the other hand are infrequent triggers. Drugs belonging to similar classification and having similar chemical structures can show cross reactivity, but here we describe a case of cross reactivity between unrelated drug classes, also known as polysensitivity.
The Case: A 58-year-old man presented with painful, burning, and pruritic blisters with ulcerations on the oral mucosa of lips, hard palate, and tip of the tongue. The patient had been on vildagliptin - metformin fixed dose combination tablets for one year. He was asked to stop the drug and lesions started improving thereafter. A week later he suffered from gastroenteritis for which he took a combined preparation of ofloxacin and ornidazole and lesions re-appeared at the same site as before with severe itching and burning.
Conclusion: This case highlights polysensitivity amongst chemically unrelated drugs, especially available in fixed-dose combination. It is an extremely rare occurrence (less than 0.2%). Moreover, there have only been a few cases of such delayed reactions occurring to gliptins, especially vildagliptin. A clinician must keep a high index of suspicion to identify this phenomenon.
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