Putative cutaneous adverse drug reaction suspected to be secondary to drug excipient and responding to brand change of pimobendan in a dog with hyperkeratotic erythema multiforme

Abstract A 16‐year‐old, spayed, female mixed terrier dog was presented with a 4‐month history of hyperkeratotic, pigmented raised papules and plaques. Histopathological examination of skin biopsies revealed a hyperplastic panepidermal cytotoxic lymphocytic dermatitis compatible with hyperkeratotic erythema multiforme. The patient had started treatment with pimobendan 2 weeks before the appearance of the lesions. A brand change of pimobendan resulted in complete healing of the lesions within 3 weeks without any treatment. This case highlights the importance of considering excipients as potential sources of cutaneous adverse drug reactions.