Time course of lepirudin plasma levels. The time course of lepirudin plasma levels from initiation of therapy until 72 hours in patients with serum creatinine levels of at least 88.4 μmol/L (10 mg/L) (▪; n = 36) or less than 10 mg/L (▴; n = 55) shows that patients with serum creatinine levels of at least 88.4 μmol/L (10 mg/L) required several days until the steady state at the aimed range was reached. Both groups were in a similar range 4 hours after start of lepirudin treatment. Therefore, aPTT should also be assessed in all patients 8 hours after start of treatment to identify those with drug accumulation.