Retension Pharmaceuticals shares fell sharply in their trading debut after the clinical-stage biopharmaceutical company's upsized initial public offering was priced at the midpoint of expectations.

Shares of the Falls Church, Va., company were recently changing hands at $10.36, down nearly 14%, after opening at $10.

Retension sold 3.75 million shares at $12 apiece in the IPO, compared with prior plans to offer 3.3 million shares at between $11 and $13 each.