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%.

The company had blamed FDA "resource constraints" for the delay, while a rival drug for hereditary angioedema received an on-time approval.

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.