Introduction: Photocontact dermatitis is a type IV delayed hypersensitivity response to an allergen that is activated by radiation energy. Its incidence is uncertain and only a small number of drugs causing such reaction have been studied. This is a case of a 67-year-old filipino male, diabetic, who presented with scaly, erythematous, and hyperpigmented plaques with areas of desquamation and erosions on sunexposed areas of the skin after taking metformin. Case: Four months prior to consult, the patient was diagnosed with type 2 diabetes mellitus and was started on metformin therapy. Days later, he started noticing scaly, erythematous and hyperpigmented plaques with areas of desquamation and erosions on sun-exposed areas, namely the upper and lower extremities, posterior neck, and forehead. There was notable sparing of areas that are usually covered with clothing such as the torso, inguina and both thighs. There were also no lesions on the scalp, palmar aspect of the hands and plantar surface of the feet. Skin biopsy was considered but was not done per patient’s preference. After discontinuation of metformin and avoidance from sun exposure, the skin lesions gradually improved. Conclusion Metformin is rarely associated with adverse skin reactions. The diagnosis of photocontact dermatitis as a side effect of metformin needs to be considered as a differential diagnosis in patients who present with skin rashes, especially in sun-exposed areas. It is recommended that there should be a high-index of suspicion for adverse drug reactions in such patients. This would reduce medical errors and medical cost and would result to prompt initiation of appropriate treatment.
Metformin ; Dermatitis, Photoallergic ; Diabetes Mellitus, Type 2