By Puyaan Singh and Siddhi Mahatole

(Reuters) -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 FDA’s decision follows an extended review of the drug last month due to heavy workloads and limited resources at the regulator.

Ekterly, which offers a convenient alternative to injectable treatments, is expected to be available by mid-July, KalVista’s financial chief Nicole Sweeny said.

The wholesale acquisition cost for the drug will be $16,720 per dose compared to other on-demand treatments that cost between $11,000 and $17,000 per dose.

Other on-demand treatments for hereditary angioedema (HAE), which affects about 8,000 people in the United States, include CSL’s Berinert, Takeda’s Cinryze, and Pharming’s Ruconest, which are administered intravenously, as well as injectables such as Takeda’s Kalbitor and Firazyr.

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.

KalVista CEO Ben Palleiko said the company anticipates U.S. sales of "the on-demand segment of the HAE market will grow by 70% (to) $1.2 billion by 2030 ... fueled by the introduction of Ekterly."

TD Cowen analyst Stacy Ku estimates peak U.S. sales of the drug at over $750 million, adding the brokerage believes "there should be high demand for Ekterly’s convenience."

Approval of the drug was based on a trial in which it achieved the beginning of symptom relief in 1.6 hours, while a later study showed it could treat attacks in 10 minutes, the company said.