KalVista Pharmaceuticals said on Monday the U.S. Food and Drug Administration has approved its drug for a type of hereditary swelling disorder, sending its shares up 33.3% in premarket trading.

The regulator's greenlight comes after it extended the review of the drug, Ekterly, due to heavy workload and limited resources.

With the approval, Ekterly becomes the first on-demand oral treatment for hereditary angioedema, offering a convenient alternative to injectable treatments.

The life-threatening condition causes sudden, dangerous swelling in the body, including the skin, digestive tract and upper respiratory system, due to deficiency in a protein known as C1 inhibitor.