Pharmacokinetics of chloramphenicol following administration of intravenous and subcutaneous chloramphenicol sodium succinate,and subcutaneous chloramphenicol,to koalas (Phascolarctos cinereus)

Clinically normal koalas (n = 19) received a single dose of intravenous (i.v.) chloramphenicol sodium succinate (SS) (25 mg/kg; n = 6), subcutaneous (s.c.) chloramphenicol SS (60 mg/kg; n = 7) or s.c. chloramphenicol base (60 mg/kg; n = 6). Serial plasma samples were collected over 24–48 h, and chloramphenicol concentrations were determined using a validated high‐performance liquid chromatography assay. The median (range) apparent clearance (CL/F) and elimination half‐life (t_1/2) of chloramphenicol after i.v. chloramphenicol SS administration were 0.52 (0.35–0.99) L/h/kg and 1.13 (0.76–1.40) h, respectively. Although the area under the concentration–time curve was comparable for the two s.c. formulations, the absorption rate‐limited disposition of chloramphenicol base resulted in a lower median C_max (2.52; range 0.75–6.80 μg/mL) and longer median t_max (8.00; range 4.00–12.00 h) than chloramphenicol SS (C_max 20.37, range 13.88–25.15 μg/mL; t_max 1.25, range 1.00–2.00 h). When these results were compared with susceptibility data for human Chlamydia isolates, the expected efficacy of the current chloramphenicol dosing regimen used in koalas to treat chlamydiosis remains uncertain and at odds with clinical observations.