Severe pleural effusion due to feline infectious peritonitis in a cat

Feline infectious peritonitis (FIP) is a progressive coronavirus-associated disease that may present in effusive, non-effusive, or mixed forms. This case report describes the clinical management of severe pleural effusion associated with effusive FIP in a 4-year-old male Himalayan cat presenting with anorexia, lethargy, weight loss, and dyspnea. Physical examination, thoracic radiography, hematology, serum biochemistry, and an FIPV antibody test supported the diagnosis. Radiographs showed massive pleural effusion that obscured the cardiac silhouette and compressed the lung fields. Therapeutic thoracocentesis removed approximately 500 mL of pleural fluid and immediately improved respiration. The cat received ampicillin-sulbactam, furosemide, hematodin, and oral molnupiravir. After 40 days, respiratory function and hematobiochemical parameters returned to normal. This case emphasizes prompt drainage of life-threatening pleural effusion and illustrates the potential clinical value of molnupiravir-based antiviral treatment for effusive FIP.