Monitoring of RXA concentration (conc.) is generally not required because of its stable pharmacokinetic and pharmacodynamic profile, even in patients with renal insufficiency. However, there are several clinical situations, in which it may be desirable to measure the RXA plasma conc. The range of RXA conc. is wide among individuals with typical peak levels of median 244 µg/L (IQR 175-360) and trough levels of median 32 µg/L (IQR 19-60) with once daily doses of 20 mg RXA.