Gilead (NASDAQ:GILD) has an unquestioned lead in hepatitis C treatment with the first mover advantage of Sovaldi. But three other companies are showing positive results. Are any a serious threat to Gilead?

Sovaldi is a cash cow                                                                                           Gilead has a blockbuster drug with Sovaldi. The drug produced $2.3 billion in sales in the first quarter of 2014. Some forecasts peg the drug to generate over $9 billion in 2017.

The company is also close to marketing a single pill combination drug for the treatment of a strain of hepatitis that makes up roughly 75% of hepatitis cases in the U.S. Ledispasvir/sofosbuvir (Sovaldi) is expected to win FDA approval by October of this year. This drug avoids using interferon or ribavirin, both of which produce negative side effects in patients.

Competitors playing catch-up                                                                           The success of Sovaldi and eventually of the dual combination drug may leave competitors such as AbbVie (NYSE:ABBV) and Bristol-Myers Squibb (NYSE:BMY) far behind.

AbbVie's drug cocktail consists of three anti-virals: ABT-450/ABT-267/ABT-333. The drug has shown impressive results in many phase 3 clinical trials, producing similarly impressive cure rates to Sovaldi.

The company filed with the FDA in mid April of this year and plans on marketing the drug before the end of 2014, which means its combination will likely be the second to market and puts it in an advantage over other competitors.

But the biggest problem for AbbVie's therapy is that it requires patients to use multiple pills each day. This lack of convenience could hurt the therapy's chances of making large inroads on Gilead.

Bristol-Myers Squibb appears to be forming a more specific strategy with its hepatitis C treatment regimen. Results from trials look on the surface to be less successful than those of competitors-showing a cure rate of 80% in certain populations. But these patients make up a harder-to-treat sample.

Furthermore, the company is clearly engaged in a strategy of targeting the Asian market. The drug will be the first to market in Japan, for instance, a full year ahead of Gilead. The drug also has had success in treating 1b genotype patients, a fact that analysts predict will make it more attractive in the Asian market, where that particular genotype is more common.

Merck is in line for silver                                                                                       Merck (NYSE:MRK) has produced a single pill therapy with its drug cocktail of MK-5172/MK-8742. The convenience of this therapy is in line with Gilead's treatment. It has also produced great results in trials -- similar to Sovaldi and AbbVie's combo.

This makes Merck, in my opinion, the most likely top challenger to Gilead in the market. There has been a great deal of trouble raised over Gilead's price -- $1,000 per day, which translates to $84,000 per treatment of its Sovaldi regimen. There is no doubt that this leaves an opening for Merck when it markets its therapy, despite the claim that there will not be much fight over price.

Everyone a success?                                                                                          Gilead will remain the undisputed leader in the treatment of hepatitis C patients. But investors should take note that competitors do have some strengths. Bristol-Myers Squibb looks prepared to capture a large part of the Asian market as well as hard-to-treat populations. Merck and Abbvie have effective drugs that should be able to find a lucrative market.