Potential for extending the chloramphenicol dosing interval for canine urinary tract infections

Canine urinary excretion of chloramphenicol was evaluated to optimize a dosing protocol for treating urinary tract infections. Seven healthy male intact purpose-bred Beagles and six healthy client-owned dogs of various breeds each received a single oral 50 mg/kg dose of chloramphenicol. Urine was collected at baseline, and 6, 8, 12, and 24 h after chloramphenicol. Chloramphenicol urine concentrations were measured and compared to the epidemiological cutoff value for E. coli (16 mcg/mL). At 8 h, mean chloramphenicol concentration from all dogs was 266.9 mcg/mL (90% CI 136.2-397.7 mcg/mL) but was lower in Beagles than client-owned dogs. At 12 h, mean chloramphenicol concentration from all dogs was 111.0 mcg/mL (90% CI 36.9-185.0 mcg/mL) and was lower in Beagles (10.6 mcg/mL, 90% CI 1.4-19.8 mcg/mL) than client-owned dogs (228.0 mcg/mL, 90% CI 103.0-353.1 mcg/mL). Urine half-life was similar for all dogs (1.8-3.8 h). This justifies dosing chloramphenicol 50 mg/kg PO q 8 h. All client-owned dogs additionally maintained concentrations well above 16 mcg/mL, for 12 h, suggesting that q 12-h dosing might be appropriate for non-Beagle dogs with susceptible lower urinary tract infections. A clinical trial in dogs with urinary tract infections is needed as well as further investigation into potential breed differences.