Influence of pre-analytical sample preparation on drug concentration measurements in peritoneal tissue: an ex-vivo study.

Objectives: Biopsy morphology (surface/depth ratio) and sample processing might affect pharmacological measurements in peritoneal tissue.

Methods: This is an ex-vivo study on inverted bovine urinary bladders (IBUB). We compared cisplatin (CIS) and doxorubicin (DOX) concentration in 81 standardized transmural punch biopsies of different diameters (6 and 12 mm). Then, we assessed the effect of dabbing the peritoneal surface before analysis. After automatized tissue homogenization with ceramic beads followed by lyophilisation, DOX concentration was quantified by high-performance liquid chromatography (HPLC), CIS concentration by atomic absorption spectroscopy. Experiments were performed in triplicate; the analysis was blinded to the sample origin. Comparisons were performed using non-parametric tests.

Results: Concentrations are given in mean (CI 5-95%). Results were reproducible between experiments (for CIS p=0.783, for DOX p=0.235) and between different localizations within the IBUB (for CIS p=0.032, for DOX p=0.663). Biopsy diameter had an influence on CIS tissue concentration (6 mm biopsies: 23.2 (20.3-26.1), vs. 12 mm biopsies: 8.1 (7.2-9.2) ng/mg, p<0.001) but not on DOX: (0.46, 0.29-0.62) vs. 0.43 (0.33-0.54) ng/mg respectively, p=0.248). Dabbing the peritoneal surface reduced DOX tissue concentration (dry biopsies: 0.28 (0.12-0.43) vs. wet biopsies: 0.64 (0.35-0.93) ng/mg, p=0.025) but not CIS (23.5 (19.0-28.0) vs. 22.9 (18.9-26.9) ng/mg, respectively, p=0.735).

Conclusions: Measurements of drug concentration in peritoneal tissue can be influenced by the biopsy's surface/depth ratio and after drying the biopsy's surface. This influence can reach a factor three, depending on the drug tested. The biopsy technique and the pre-analytical sample preparation should be standardized to ensure reliable pharmacological measurements in peritoneal tissue.