KalVista Pharmaceuticals said on Monday the U.S. Food and Drug Administration has approved its drug, the first on-demand oral treatment for a type of hereditary swelling disorder, sending its shares up more than 18%.

KalVista Pharma has finally received FDA approval for its oral kallikrein inhibitor sebetralstat, becoming the first treatment in the US that can provide oral, on-demand treatment of hereditary angioedema (HAE) attacks.

KalVista's journey to FDA approval wasn't smooth sailing, with an unexpected delay and alleged behind-the-scenes drama at the regulatory agency.