In Arm B, Period 2, subjects will receive nitisinone for 15 consecutive days (14 days on nitisinone only and one day on nitisinone + substrate). No nitisinone steady state PK characterization will be conducted in this arm. On the last treatment day, the subjects will receive nitisinone together with the OAT1/OAT3 substrate. This will be followed by 8 hours of blood sampling for determination of substrate PK.