SUN-630 - A Case of Injection Site Hyperpigmentation Due to Mounjaro

Mounjaro (tirzepatide) is a dual agonist of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) used for glycemic control, weight loss and cardiovascular risk reduction. The most well described side effects in this class of medications include gastrointestinal upset with nausea, vomiting, acute pancreatitis, abdominal pain, indigestion, diarrhea and constipation. To our knowledge, there are only rare reports of local injection site hyperpigmentation. This case aims to bring awareness to this adverse effect.

54-year-old female follows for type 2 diabetes mellitus that is sub-optimally controlled with a hemoglobin A1c of 7.5% on oral anti glycemic agents alone. She was initiated on Mounjaro to further optimize glycemic control. Soon after starting this medication, she reported new areas of hyperpigmentation and pruritis at the injection sites. She denied similar skin reactions in the past. There was no swelling, erythema, or associated urticarial rash. The reaction was strictly local without any systemic effects. She was evaluated by dermatology who felt the hyperpigmentation was a local inflammatory reaction. The patient had a strong preference to continue with the medication as she had a successful 20lb weight loss and improvement in hemoglobin A1c from 7.5% to 5.5%. A transition from Mounjaro to Zepbound (tirzepatide) with the same dosing was recommended. Although both medications contain the same active ingredient, Zepbound is a preservative-free formulation while Mounjaro can include benzyl alcohol, phenol, or glycerol depending on manufacturing site or distribution region. The patient reported significant improvement in the hyperpigmentation and pruritis after the first injection of Zepbound. She had complete resolution of local symptoms after the second dose of preservative-free formulation.

Tirzepatide has been shown to have a higher proportion of dermatologic reactions when compared to alternative GLP-1 agonists. Even with this trend, the incidence of injection site reactions overall is rare. There are even fewer reports describing local reactions associated with hyperpigmentation. We aim to highlight an uncommon case of local hyperpigmentation reaction with Mounjaro use. Tirzepatide is sold as both Zepbound and Mounjaro. These two branded medications are therapeutically equivalent, and as such, there are no current head-to-head trials comparing their differences in adverse reactions. We hope to increase awareness that formulations of Mounjaro can include additive ingredients based on the manufacturing site. This could lead to a clinical difference in prevalence of local adverse reactions, and plausible reason to switch to a preservative-free formulation if such reactions occur. We illustrate a case of hyperpigmentation reaction reversal after switching to a preservative-free formulation of tirzepatide, Zepbound

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