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255 ENZYMATIC & GAS CHROMATOGRAPHY/MASS SPECTROMETRY ANALYSIS OF CHLORAMPHENICOL IN NEWBORN INFANTS

Enzymatic and gas chromatography/mass spectrometry (GC/MS) assays for chloramphenicol (CM) were developed to assist in study of the pharmacology of CM and to establish parameters for monitoring its use. An enzymatic assay based on the specific acetylation of CM with a radioactively labeled acetyl group derived from (14C) acetyl coenzyme A and catalyzed using acetyltransferase prepared by two different methods was established. Results were similar when acetyltransferase enzyme prepared by either method was used. Standard curves were linear to 100 μg/ml. Six other antibiotics did not accept an acetyl group or inhibit acetylation of CM when incubated with CM at 37°C for 3 days. The enzymatic assay was compared to the GC/MS method for determination of CM in over 150 serum and CSF samples obtained from patients receiving CM. A significant correlation existed between the GC/MS and the acetylation assay (y=1.05 × -0.20, r=0.998). The sensitivity of the assays was 1 μg/ml and the precision was ±3%. Infants had dosing adjustments made to achieve peak and trough concentrations in serum of approximately 20 and 10 μg/ml. Therapeutic monitoring of CM provides a means for increasing therapeutic efficacy and avoiding toxicity in newborn infants and in patients with hepatic and renal dysfunction.