Annexon shares fall on clinical trial update

Shares of Annexon Inc. (NASDAQ: ANXN) fell 12% in midday trading on Friday after the biopharmaceutical company announced a temporary pause in dosing for a phase 2 clinical trial of its experimental therapy ANX005.

The company said the pause was implemented as a precautionary measure following an unexpected adverse event observed in one patient. Annexon did not disclose further details about the event or the trial's timeline, but stated that it is working closely with regulators and investigators to assess the situation.

The phase 2 trial, known as ARCHER-2, is evaluating ANX005 in patients with geographic atrophy, a leading cause of blindness. The therapy targets the complement system, a part of the immune system implicated in the progression of the disease. Annexon had previously reported positive interim data from the trial, which contributed to a 20% rally in its shares over the prior month.

Investors reacted swiftly to the news, with Annexon's stock declining to $18.50 by midday, down from $21.00 at Thursday's close. The drop erased nearly $80 million in market capitalization. Trading volume surged to more than 1.8 million shares, well above the 30-day average of 750,000 shares.

Annexon emphasized that the dosing pause does not indicate a failure of the therapy and that the company remains committed to advancing its pipeline. The pause is expected to last for at least several weeks as the company gathers additional data and consults with regulatory authorities.

Analysts at William Blair maintained their outperform rating on Annexon, citing the long-term potential of ANX005 despite the short-term setback. The firm reiterated a price target of $30, suggesting more than 60% upside from current levels.

The incident underscores the inherent risks in biotechnology investing, where clinical trial outcomes can significantly impact stock performance. Annexon's next update on the trial is expected in the coming months, pending regulatory feedback.