Patients w/ WHO class I functional pulmonary arterial HTN; not recommended in patients w/ moderate hepatic impairment. Obtain liver enzyme tests prior to initiation. Monitor mthly of ALT & AST & for signs of hepatic injury. Severe anaemia; measure Hb conc prior to initiation of treatment & repeat tests during treatment. Patients w/ veno-occlussive disease. Concomitant use w/ strong CYP3A4 inducers (eg, rifampicin, St. John's wort, carbamazepine & phenyotin) & strong CYP3A4 inhibitors (eg, itraconazole, ketoconazole, voriconazole clarithromycin, telithromycin, nefazodone, ritonavir & saquinavir). Galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption; hypersensitive to soya. May have a minor influence on the ability to drive & use machines. Elderly >75 yr.