Adverse interaction between colchicine and ketoconazole in a Chinese shar pei

A Chinese shar pei with a 2 yr history of episodic fever, lethargy, and shifting lameness was presumptively diagnosed with familial shar pei fever but had never been treated for the syndrome. After being presented for a superficial pyoderma with possible dermatophyte coinfection, treatment with a cephalosporin and ketoconazole were prescribed. One wk later, colchicine was initiated for familial shar pei fever using cautious dose escalation. Nevertheless, gastrointestinal toxicity, skeletal muscle myopathy, and hepatotoxicity developed within 2 wk. Abrupt resolution of gastrointestinal toxicity and myopathy followed drug withdrawal. However, escalating liver enzyme activity and hyperbilirubinemia led to liver biopsy to rule out an antecedent hepatopathy. Biopsy characterized canalicular cholestasis and colchicine-associated metaphase arrest and ring mitoses reflecting repression of mitotic spindle formation. Signs of illness completely resolved 3 mo after drug discontinuation. Although avoidable adverse interactions between ketoconazole and drugs reliant on cytochrome oxidase biotransformation and/or drug efflux mediated by multiple drug-resistant transporters are well documented in humans, these are rarely reported in veterinary patients. This case exemplifies an important and avoidable ketoconazole/colchicine drug interaction from which the patient completely recovered. The dog tested negative for the canine MDR1 loss of function mutation that also might potentiate colchicine toxicity.