Functional testing of tranexamic acid effects in patients undergoing elective orthopaedic surgery

Tranexamic acid (TXA) can reduce blood loss and transfusion rates in orthopaedic surgery. In this regard, a new viscoelastometric test (TPA-test, ClotPro), enables the monitoring of TXA effects. This prospective observational study evaluated and correlated TXA plasma concentrations (cTXA) following intravenous and oral administration in patients undergoing elective orthopaedic surgery with lysis variables of TPA-test. Blood samples of 42 patients were evaluated before TXA application and 2, 6, 12, 24 and 48 h afterwards. TPA-test was used to determine lysis time (LT) as well as maximum lysis (ML) and cTXA was measured using Ultra-High-Performance-Liquid-Chromatography/Mass-Spectrometry. Data are presented as median (min-max). LT_TPA-test and ML_TPA-test correlated with cTXA (r = 0.9456/r = 0.5362; p < 0.0001). 2 h after intravenous TXA administration all samples showed complete lysis inhibition (LT_TPA-test prolongation: T1: 217 s (161-529) vs. T2: 4500 s (4500-4500);p < 0.0001), whereas after oral application high intraindividual variability was observed as some samples showed only moderate changes in LT_TPA-test (T1: 236 s (180-360) vs. T2: 4500 s (460-4500); p < 0.0001). Nevertheless, statistically LT_TPA-test did not differ between groups. ML_TPA-test differed 2 h after application (i.v.: 9.0% (5-14) vs. oral: 31% (8-97); p = 0.0081). In 17/21 samples after oral and 0/21 samples after intravenous administration cTXA was < 10 µg ml^-1 2 h after application. TPA-test correlated with cTXA. ML_TPA-test differed between intravenous and oral application 2 h after application. Most patients with oral application had TXA plasma concentration < 10 µg ml^-1. The duration of action did not differ between intravenous and oral application. Additional studies evaluating clinical outcomes and side-effects based on individualized TXA prophylaxis/therapy are required.