Mirabegron-induced acute urticaria: An uncommon cutaneous adverse drug reaction

Sir, Urticaria is the second most common drug-induced skin lesion after morbilliform eruption.[1] Mirabegron is a beta-3-adrenergic receptor agonist and is frequently prescribed to treat urinary urge incontinence as well as overactive bladder.[2,3] Here, we report the case of a patient with urticaria following intake of mirabegron 50 mg once daily. A 61-year-old male attended the dermatology outpatient department, with multiple erythematous evanescent plaques along with itching and burning sensation over the trunk and upper extremities, present for the last 3 days. The patient was diagnosed with a urinary bladder tumor 3 months back and was being treated with flavoxate and tolterodine. Recently 7 days back, he was prescribed mirabegron 50 mg once daily, 4 days following which he developed urticarial lesions along with pruritus. After each dose of mirabegron, the patient developed these lesions which subsided within 12 h of drug intake. There was no history of angioedema. Cutaneous examination revealed multiple, erythematous, pruritic macules and plaques that showed blanching on diascopy [Figures 1 and 2]. Dermatographism was positive. Blood pressure, pulse rate, respiratory rate, and SpO2 were within normal limits. Complete blood count revealed leukocytosis (11,000 cells/mm3) with high eosinophil count (600 cells/mm3). Liver function test and kidney function test were within normal limits. The patient was diagnosed as a case of mirabegron-induced acute urticaria. As per the Naranjo Adverse Drug Reaction probability scale and the WHO Uppsala Monitoring Centre Scale, the reaction was labeled as “probable.” According to the Hartwig’s Severity Assessment Scale, it was classified as “Level 3.” Oral provocation test could not be performed on account of ethical reasons. He was treated with desloratadine 5 mg twice daily for 2 weeks along with application of light liquid paraffin and white soft paraffin. The lesions resolved within 3 days and the pruritus reduced. He was advised to continue flavoxate and tolterodine.Figure 1: Erythematous and edematous papules and plaques over the trunk and abdomenFigure 2: Erythematous and edematous papules coalescing to plaques over the forearms, bilaterallyMirabegron (beta-3-receptor agonist) received FDA approval in 2012 for the treatment of overactive bladder. The most common adverse effects include dysuria, passage of hard stools, and a significant rise in residual urinary volume. The United States FDA has also considered the possibility of generalized itching, mirabegron as a potential cause of pruritus, vasculitis, urticarial, angioedema, and purpuric lesions. There have been a few reports on angioedema[4] and serum sickness like illness[5] caused by mirabegron. However, the development of urticarial following intake of mirabegron is hardly reported in the literature, and this prompted us to present the case. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.