Fluctuations in levels of serum creatinine with deferasirox therapy have also been the subject of concern. In a multicenter randomized phase 3 registration trial comparing deferasirox and deferoxamine therapy in patients with β-thalassemia major, mild, dose-dependent increases in serum creatinine were observed in 38% of patients receiving deferasirox at dosages of 20–30 mg/kg per day. These increases were sometimes transient, were mostly within the normal range, and did not exceed twice the upper limit of normal. Dose reductions were required in only 13% of patients receiving deferasirox. In about 25% of these patients, levels of serum creatinine returned to baseline, and in the remainder of patients it remained stable or fluctuated between baseline and the maximum increase observed before dose reduction.27 Safety data with deferasirox in children and adults with β-thalassemia major have now been reported for up to 5 years of treatment and confirm absence of progressive increases in serum creatinine over longer-term treatment,28 even in patients with heavy iron load who require dose escalation to >30 mg/kg per day.29 Studies on levels of cystatin C in patients with β-thalassemia major receiving deferasirox for up to 9 months also confirm that changes are stable over the treatment period.25