Oral chloramphenicol dosage regimens in cats

Five adult domestic cats were each given three separate 3‐day courses of chloramphenicol, using a different oral‐dosage regimen each time. The regimens were: 120 mg/kg/day divided 8‐hourly, 60 mg/kg/day divided 8‐hourly, and 50 mg per cat every 12 h (25–40 mg/kg/day). The interval between successive courses was 3 weeks. On the third day of each course plasma samples were obtained at fixed intervals after dosing and were assayed chemically for chloramphenicol. The ranges from peak to trough chloramphenicol concentrations with each regimen were (values are means ± SEM): 63.8 ± 4.60 to 43.0 ± 3.32 μg/ml (120 mg/kg/day), 42.0 ± 3.63 to 24.7 ± 1.83 μg/ml (60 mg/kg/day), and 24.3 ± 1.72 to 7.5 ± 0.85 μg/ml (50 mg per cat 12‐hourly). Because of these findings, previous toxicity studies, and the proposed therapeutic (effective and safe) concentration for chloramphenicol of 5–15 μg/ml, it is suggested that a regimen of 50 mg per animal every 12 h could be adequate for chloramphenicol therapy in cats of average size (2.5‐3.9 kg) and should be evaluated clinically.