Acute hepatitis and haemolysis associated with doxycycline and rifampin administration in two weanling foals

Two foals were being treated with a combination of oral doxycycline and rifampin for presumed Rhodococcus equi infections. After 3–4 weeks of antimicrobial administration, both foals presented with icterus and nonspecific clinical signs, including lethargy and inappetence. Diagnostic evaluation, including clinicopathologic testing, ultrasonography and liver biopsy, documented evidence of toxic hepatopathy and anaemia. An acute drug reaction was suspected based on histopathologic evidence observed on liver biopsy samples, the resolution of clinical and clinicopathologic abnormalities once antimicrobials were discontinued, and anecdotal reports from other investigators. Serial monitoring of liver enzyme activities documented the resolution of hepatopathy over several weeks with limited supportive therapy, and both foals survived to adulthood. Although uncommon, equine practitioners should be aware that hepatopathy and anaemia can be observed with oral administration of doxycycline and rifampin in foals.