Portola tanks as blood clot drug trial disappoints

US biotech firm Portola Pharmaceuticals (Nasdaq: PTLA) saw its shares tumble 29% to $20.40 in active pre-market trading on Thursday after Phase III clinical trial results of its oral blood thinner betrixaban missed study thresholds.

Portola announced top-line data from the Phase III APEX (Acute Medically Ill VTE Prevention with Extended Duration Betrixaban) Study, which evaluated the superiority of extended-duration anticoagulation with oral betrixaban compared with standard of care anticoagulation with injectable enoxaparin for the prevention of venous thromboembolism (VTE), or blood clots, in acute medically ill patients. These are patients who are hospitalized for serious common medical conditions, such as heart failure, stroke, infection and pulmonary disease.

The primary efficacy and safety analysis consisted of three pre-specified patient groups of increasing sample size: Cohort 1 - patients with elevated D-dimer levels (62% of the overall study population), Cohort 2 - patients with elevated D-dimer levels or age ≥75 years (91% of the overall study population), and the overall study population. By protocol definition, primary efficacy analysis testing of Cohort 1 was done first and required a p value of 0.05 or less in order to test Cohort 2, which in turn required a p value of 0.05 or less in order to test the overall study population.