- Two times of venous blood sampling will be carried out at steady state. Three ml of venous blood is sampled right before the morning dose (trough sampling). The second sampling is carried out at any time point within 2-4 hours after the morning dose (peak sampling). To obtain the exact dose and sampling history, at least three dosing times around the trough and peak sampling will be recorded to the minute. Sampling time will also be recorded as clock time.