Pimobendan Toxicosis in Dogs

Pimobendan, approved for treating canine congestive heart failure, has a dose range of 0.2–0.6 mg/kg PO q12h and apparently wide safety margin. However, because of the chewable tablet flavor, accidental ingestion and overdosing occurs. Seven dogs with suspected pimobendan toxicosis were evaluated via records from an animal poison control database. A toxic dose was defined either as suspected ingestion ≥0.6 mg/kg q12h if signs were present, or >2 mg/kg regardless of whether signs were present. Signs were seen in 5 dogs and included severe tachycardia (n = 4), mild hypotension (n = 2), hypertension (n = 2), and new transient heart murmur (n = 1). Two dogs showed no signs. Decontamination via emesis and activated charcoal was performed in all cases, followed by hospitalization for monitoring and supportive care. Outcomes were uniformly good; all dogs survived to discharge within 24 hours of suspected exposure. One dog died 3 days after presumptive pimobendan overdose, possibly from preexisting cardiac disease. The uncertain amount and time of pimobendan ingestion were major limitations. The authors concluded that pimobendan toxicosis in healthy dogs is fairly benign, although care should be taken in cases of preexisting cardiovascular disease.

Commentary

Pimobendan is increasingly used in veterinary medicine. Both hyper- and hypotension were reported in the accidental overdoses; whether this is related to the underlying disease and the body’s compensation mechanisms is unknown. Dogs with underlying cardiac disease can be more difficult to manage than healthy dogs; fluids, colloids, and other cardiac medications must be used with caution in these patients. This is also a good reminder that chewable medications can be a double-edged sword—they enhance pill administration but may encourage ingestion, leading to overdose.—Tina Wismer, DVM, DABVT, DABT

Source

Clinical signs of cardiovascular effects secondary to suspected pimobendan toxicosis in five dogs. Reinker LN, Lee JA, Hovda LR, Rishniw M. JAAHA 48:250-255, 2012.