The primary UGT enzymes responsible for chloramphenicol O-glucuronidation were evaluated in vitro. Reaction phenotyping for the glucuronidation of chloramphenicol with 12 expressed human liver UGT isoforms has identified UGT2B7 as having the highest activity for 3-O- and 1-O-chloramphenicol glucuronidation with minor contributions from UGT1A6 and UGT1A9. The formation of 1-O-chloramphenicol glucuronide by pooled HLM and expressed UGT2B7 exhibited substrate inhibition kinetics with apparent K(m) values of 408.2 and 115.0 microM, respectively. Azidothymidine (AZT) and hyodeoxycholic acid (substrates of UGT2B7) inhibited 3-O- and 1-O-chloramphenicol glucuronidation in pooled HLMs. In 10 donor HLM preparations, both chloramphenicol 3-O- and chloramphenicol 1-O-glucuronidation showed a significant correlation with AZT glucuronidation (UGT2B7) at 30 µM chloramphenicol. These results suggest that UGT2B7 is the primary human hepatic UDP-glucuronosyltransferase isoform catalyzing 3-O- and 1-O-chloramphenicol glucuronidation with minor contributions from UGT1A6 and UGT1A9.
Identification of human UGT2B7 as the major isoform involved in the O-glucuronidation of chloramphenicol. Chen M, LeDuc B, Kerr S, Howe D, Williams DA. Drug Metab Dispos. 2010 Mar;38(3):368-75.

An in vitro study screened the effect of 55 molecules, representative of 20 different therapeutic classes, on 3'-azido-3'-deoxythymidine (AZT) glucuronidation by human liver microsomes. At high concentrations, chloramphenicol caused more than 90% inhibition of AZT glucuronidation, in vitro. For compounds that appeared to inhibit AZT glucuronidation, extrapolation to the clinical situation must take into account both the in vitro apparent Ki values and the usual expected plasma level for the coadministered drug. By considering these parameters, this work indicates that clinically relevant inhibition of AZT glucuronidation may be observed with chloramphenicol. Clinical and pharmacokinetic studies are required to validate these results.
3'-azido-3'-deoxythymidine drug interactions. Screening for inhibitors in human liver microsomes. Rajaonarison JF, Lacarelle B, Catalin J, Placidi M, Rahmani R. Drug Metab Dispos. 1992 Jul-Aug;20(4):578-84.

A study examined the effect of a number of drugs which themselves undergo glucuronidation on AZT conjugation by human liver microsomes in vitro. Inhibitory effects were seen with chloramphenicol, with enzyme activity decreased by 88.7% at a concentration of 10 mM. Further studies are necessary to characterise the inhibition observed but the method described enables a screen of potentially important drug interactions to be carried out.
The effect of various drugs on the glucuronidation of zidovudine (azidothymidine; AZT) by human liver microsomes. Sim SM, Back DJ, Breckenridge AM. Br J Clin Pharmacol. 1991 Jul;32(1):17-21.