Pfizer reported positive data from an open-label extension to the pivotal Phase II/III trial evaluating tafamidis in the treatment of transthyretin familial amyloid polyneuropathy (TTR-FAP). The 12-month extension study (Fx-006) in 87 patients showed that treatment with tafamidis slowed disease progression over 30 months.
The positive data come less than a week after FDA issued Pfizer a refusal to file letter for tafamidis, stating that the application, which was submitted in February, was not sufficiently complete to permit a substantive review. The company says that the additional information needed to support this filing is available without further clinical studies.
The original Fx-005 study evaluated oral tafamidis once-daily in comparison with placebo in 128 patients. This 18-month study missed its co-primary endpoints measured by the neuropathy impairment score—lower limb (NIS-LL) scale, and quality of life measured by the Norfolk Q@OL-diabetic neuropathy scale, in the intent to treat population. However, the study met statistical significance in a predefined secondary analysis (efficacy evaluable population), which was designed to adjust for the impact of patient attrition due to liver transplantation.
Patients treated with the investigational drug for the whole 30-month duration of the original 18-month placebo-controlled Phase II/III study (Fx-005) plus the 12-month extension study demonstrated less neurological deterioration than those who entered the extension trial having received placebo for the original Phase II/III study. Patients treated with tafamidis over 30 months also demonstrated better preservation of large and small nerve fiber function than those only treated for 12 months.
Benefits of tafamidis therapy in terms of slowed disease progression were also seen among patients with severe disease who started treatment with the Pfizer drug after an initial 18 months of initial placebo therapy.
TTP-FAP is a genetic neurodegenerative disease that affects about 8,000 patients worldwide, Pfizer notes. Life expectancy for untreated patients is about 10 years from the time of symptom onset. The disease results from destabilization of TTP that leads to the formation of misfolded proteins and subsequent amyloid fibrils in the peripheral and autonomic nerves, and in other organs including the GI tract, kidneys, and heart.