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Antimicrobial Agents and Chemotherapy, September 1998, p. 2259-2261, Vol. 42, No. 9
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Influence of Assay Methodology on the Measurement of Free Serum Ceftriaxone Concentrations

Sue J. Kohlhepp,1,* David N. Gilbert,1,2 and James E. Leggett1,2

Earle A. Chiles Research Institute, Providence Portland Medical Center,1 and Oregon Health Sciences University,2 Portland, Oregon

Received 21 July 1997/Returned for modification 31 January 1998/Accepted 10 June 1998

The influence of assay methodology on the measurement of the active free fraction of ceftriaxone in plasma was determined. The free fraction was measured by three methods: agar diffusion bioassay, precipitation of plasma protein with methanol followed by high-performance liquid chromatography (HPLC) of the supernatant, and ultrafiltration of plasma followed by HPLC of the filtrate. In human serum, the free ceftriaxone levels were significantly lower (P = 0.03) when measured on ultrafiltrates compared to the other two methods. This difference disappeared when dolphin serum was studied. After ultrafiltration, human serum was shown, by Scatchard plot analysis, to have two ceftriaxone binding sites. Species differences were also demonstrated. Hence, in humans, determination of free plasma ceftriaxone varies with the assay method employed.

* Corresponding author. Mailing address: Earle A. Chiles Research Institute, Providence Portland Medical Center, 4805 NE Glisan, Portland, OR 97213. Phone: (503) 215-6140. Fax: (503) 215-6052. E-mail: sue_kohlhepp{at}phsor.org.

Antimicrobial Agents and Chemotherapy, September 1998, p. 2259-2261, Vol. 42, No. 9
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.




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