What happened
No biotech investor likes when a large percentage of patients walk away from an important clinical trial. After Annexon (ANNX -10.36%) revealed that this occurred in an otherwise encouraging study of its ANX005, a pipeline drug aimed at treating Huntington's disease, the company's shares tumbled by over 34% on the day.
So what
After market hours on Tuesday, Annexon reported interim results from an ongoing, open-label Phase 2 clinical trial of ANX005. The data concerned patients who completed the full 24-week course of treatment and revealed that the drug demonstrated "full target engagement of C1q in both serum and cerebrospinal fluid observed in evaluable patients through the dosing period."
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Annexon's pipeline programs center around autoimmune and neurodegenerative disorders triggered by errors with C1q, a key protein.
The biotech added that ANX005 was generally well-tolerated, although two recipients experienced drug-related serious adverse events.
For the most part, though, according to Annexon, "Evaluable patients maintained clinical function, as measured by changes in mean Composite Unified Huntington's Disease Rating Scale (cUHDRS), relative to baseline after six months of treatment, and improvement in cUHDRS was observed in more than half of all evaluable patients and in 75% of evaluable patients who showed excess complement activity at baseline."
Now what
The very big "but" in Annexon's report is that five patients in the 28-participant trial discontinued the treatment during the trial, and three of those defections were because of a drug-related adverse event (including the two people that experienced serious adverse events). That's a high percentage by any standard.
Annexon said that it expects full data from the Phase 2 study to be available in Q2.
