A Dose Escalation Study of the Pharmacokinetics, Safety & Efficacy of Deferitrin, an Oral Iron Chelator in Beta Thalassaemia Patients.

Iron accumulation and overload in beta thalassaemia patients are associated with significant morbidity and mortality. Iron chelators are used to manage iron accumulation but side effects and compliance issues restrict the use of available chelators. Deferitrin (Genzyme Corporation) is an orally available iron chelator intended for iron overload.

Method: Patients were dosed in 4 cohorts, receiving 5, 10, 15 and 25 mg/kg/day of deferitrin. Deferitrin dosing in cohorts 1–3 was once daily for 12 weeks. Cohort 4 received deferitrin twice daily (BD) for 48 weeks (12.5mg/kg BD, 25 mg/kg/day). Pharmacokinetics (PK) were assessed in a subset of up to 5 patients in each cohort, pre-dose and 1, 2, 4 and 8 hours post dose. All patients had trough levels assessed at weeks 1, 6 and 12 (all Cohorts) and additionally at weeks 24, 36 and 48 for Cohort 4. PK parameters were determined by model independent (non-compartmental) analyses. Safety was assessed by collection of adverse events and laboratory assessments with renal parameters measured weekly due to observations of renal toxicity in preclinical testing. Efficacy (change in liver iron concentration (LIC)) was assessed by SQUID (superconducting quantum interference device) in Turin, Italy, between screening and end of study. Iron excretion and intake were estimated by calculation:

1. Iron excretion due to deferitrin = Iron Intake (mg/kg/day) - TBI (mg/kg/day)

2. Iron Intake (mg/kg/day) = [total mL pRBC (exclude last BT×) × 1.08] / [Weight (kg) × Days (Between 1st & last BT×)]

3. TBI (mg/kg/day) = Change in LIC (mg Fe/g dry weight) × [10.6 (Angelucci Factor) / D (Days on deferitrin)] Key: pRBC = packed red blood cells, BT× = blood transfusion, TBI=Total Body Iron.

Results: PK: PK for deferitrin dosed once daily was linear and dose proportional. The serum half-life was 1.3–1.8 hrs, clearance was 226–340 mL/min and mean residence time was 2.8–3.4 hrs for once daily dosing. PK data from BD dosing is not yet available. Safety: Deferitrin dosed once daily was generally well tolerated (Cohorts 1–3). Slight rises in transaminases were seen at 10 and 15 mg/kg/day. A large proportion of enrolled patients were hepatitis C positive (73%). When dosed BD (12.5 mg/kg BD in Cohort 4), 3 patients developed renal toxicity after 4–5 weeks of treatment. Two patients experienced increased proteinuria (max 3.73 g/L & 3.29 g/L) and one patient suffered acute renal failure (peak serum creatinine 4.1 mg/dL, lowest GFR 27 mmol/L). All patients recovered normal renal function after stopping treatment. No patients were re-challenged with deferitrin. Dosing was terminated in all patients because of safety concerns. Efficacy: Mean iron excretion in mg/kg/day (S.D) for Cohort 1 was 0.22 (0.22), Cohort 2 was 0.45 (0.14) and Cohort 3 was 0.33 (0.12). The reasons for the lack of dose proportionality in iron excretion are unclear. Efficacy could not be assessed in Cohort 4 due to early termination of the study.

Conclusions: Deferitrin dosed once daily was generally well tolerated and associated with a mean iron excretion of 0.34 mg/kg/day. Deferitrin dosed BD (12.5mg/kg BD) was associated with unacceptable renal toxicity and led to study termination. Deferitrin does not appear to have an acceptable therapeutic margin to allow sufficient iron excretion for long-term administration.