Journal of Pharmaceutical and Biomedical Analysis 29 (2002) 17–33 Determination of meropenem in plasma and filtrate-dialysate from patients under continuous veno-venous haemodiafiltration by SPE-LC C. Robatel a , T. Buclin a , P. Eckert b,1 , M.D. Schaller b , J. Biollaz a , L.A. Decosterd a, * a De ´partement de Me ´decine, Diision de Pharmacologie Clinique, Laboratoire BH 18 -218, Centre Hospitalier Uniersitaire Vaudois (CHUV), 1011 Lausanne, Switzerland b De ´partement de Me ´decine, Soins Intensifs de Me ´decine, Centre Hospitalier Uniersitaire Vaudois (CHUV), 1011 Lausanne, Switzerland Received 31 October 2001; received in revised form 29 November 2001; accepted 16 December 2001 Abstract Meropenem, a carbapenem antibiotic displaying a broad spectrum of antibacterial activity, is administered in Medical Intensive Care Unit to critically ill patients undergoing continuous veno-venous haemodiafiltration (CVVHDF). However, there are limited data available to substantial rational dosing decisions in this condition. In an attempt to refine our knowledge and propose a rationally designed dosage regimen, we have developed a HPLC method to determine meropenem after solid-phase extraction (SPE) of plasma and dialysate fluids obtained from patients under CVVHDF. The assay comprises the simultaneous measurement of meropenem’s open-ring metabolite UK-1a, whose fate has never been studied in CVVHDF patients. The clean-up procedure involved a SPE on C18 cartridge. Matrix components were eliminated with phosphate buffer pH 7.4 followed by 15:85 MeOH – phosphate buffer pH 7.4. Meropenem and UK-1a were subsequently desorbed with MeOH. The eluates were evaporated under nitrogen at room temperature (RT) and reconstituted in phosphate buffer pH 7.4. Separation was performed at RT on a Nucleosil 100–5 m C18 AB cartridge column (125 ×4 mm I.D.) equipped with a guard column (8 ×4 mm I.D.) with UV–DAD detection set at 208 nm. The mobile phase was 1 ml min -1 , using a step-wise gradient elution program: %MeOH/0.005 M tetrabutylammonium chloride pH 7.4; 10/90–50/50 in 27 min. Over the range of 5–100 g ml -1 , the regression coefficient of the calibration curves (plasma and dialysate) were 0.998. The absolute extraction recoveries of meropenem and UK-1a in plasma and filtrate-dialysate were stable and ranged from 88 – 93 to 72–77% for meropenem, and from 95–104 to 75–82% for UK-1a. In plasma and filtrate-dialysate, respectively, the mean intra-assay precision was 4.1 and 2.6% for meropenem and 4.2 and 3.7% for UK-1a. The inter-assay variability was 2.8 and 3.6% for meropenem and 2.3 and 2.8% for UK-1a. The accuracy was satisfactory for both meropenem and UK-1a with deviation never exceeding 9.0% of the nominal concentrations. The stability of meropenem, studied www.elsevier.com/locate/jpba * Corresponding author. Tel.: +41-21-314-4272; fax: +41-21-314-4288. E-mail address: laurentarthur.decosterd@chuv.hospvd.ch (L.A. Decosterd). 1 Present address: Hopital Re ´gional de Sion, CH-1950 Sion, Switzerland. 0731-7085/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0731-7085(02)00022-5