Dermatologic adverse effect of subcutaneous furosemide administration in a cat

Background: Furosemide is a mainstay of treatment in congestive heart failure (CHF) and is widely prescribed to dogs and cats by several formulations, including the subcutaneous one. In canine and human medicine, dermatologic adverse effects of subcutaneous furosemide (SF) have been documented; conversely, no prior case has been published describing skin reactions to this therapeutic protocol in cats. In this report, we describe, for the first time in feline medicine, a suspected dermatologic adverse effect after SF in a cat. Case description: A 2-year-old domestic shorthair cat was presented for CHF associated with lung edema and pleural effusion. Echocardiography revealed asymmetric left ventricular myocardial thickening and severe left atrial dilation. The cat was hospitalized and initially treated with oxygen, intravenous furosemide, and clopidogrel. After discharge, the route of administration of furosemide was switched from intravenous to oral. Within the following 2 weeks, the cat experienced two relapses of lung edema despite the progressive increase of the furosemide dose, the addition of spironolactone and adherence to the therapeutic protocol by the owners. The dose of furosemide was further increased and its route of administration at home was switched from oral to parental. As the owner was not able to administrate intramuscular injections, SF was prescribed. This allowed the prevention of further episodes of lung edema. However, although the cat had never presented skin problems before, multiple well-defined circular, crusted ulcerative cutaneous lesions associated with alopecia developed at the sites of furosemide injections 2 weeks later. After ruling out several differential diagnoses for these lesions, a rare side effect of furosemide, not yet described in cats but already known in canine and human medicine, was strongly suspected as the possible cause. Therefore, the ongoing injectable formulation of furosemide was interrupted and substituted with an alternative brand, maintaining the same dose and route of administration. Thanks to this change, the dermal ulcerations disappeared within 1 month. Subsequently, the cat experienced neither further skin problems nor a recurrence of lung edema. Conclusion: Although SF is sometimes prescribed in small animal practice, it should be noticed that this may lead to dermatologic adverse reactions in the cat.