AbbVie, Bristol-Myers Squibb, Merck, Johnson & Johnson and others are also developing all-oral regimens for hepatitis C that could reach the market in the next one to three years.

Some analysts expect Sovaldi to become one of the best-selling drugs in the world. Matthew Roden, an analyst at UBS, said in a note on Friday that annual sales could surpass the record of around $13 billion achieved by Lipitor, from Pfizer, in its peak year.

Sales are expected to be strong from the start, because many patients, on the advice of their doctors, have been putting off starting treatment until Sovaldi became available.

One person waiting is Tom Espinosa, a building inspector in Oakland, Calif. He has tried the existing drugs and some experimental ones, without success, so this drug might be his last chance. His liver is already deteriorating badly, but he is hoping the new drug will stop the progression.

Other companies are trying to get at least a little piece of Gilead’s bounty. Merck, Roche and Idenix Pharmaceuticals are separately claiming that Sovaldi infringes on patents they hold. Should any of those companies prevail, it is expected they will receive royalties, not keep the drug off the market.

Until two years ago, the treatment for hepatitis C consisted of 24 to 48 weeks of weekly injections of interferon alfa combined with daily tablets of ribavirin. Neither drug was developed specifically to treat hepatitis C. The combination cured about half of patients, but the side effects, including flulike symptoms, anemia and depression, could be severe.

Sovaldi and newer drugs work by inhibiting enzymes produced by the hepatitis C virus. This is the same approach that was used to make drugs for H.I.V. As in H.I.V., two or more of these drugs for hepatitis C must be used together, to prevent the virus from developing resistance.