BOSTON (TheStreet) -- Merck's(MRK) - Get Report initial effort to developer a superior hepatitis C therapy and leapfrog over Gilead Sciences (GILD) - Get Report has fallen short.

A triple therapy combining two experimental Merck drugs with Gilead's Sovaldi yielded interim hepatitis C cure rates for genotype 1 patients ranging from 80% to 87% following six to eight weeks of treatment. A four-week treatment schedule of the same three-drug regimen resulted in a "sub-optimal" hepatitis C interim cure rate of only 39%, Merck reported Monday from the American Association for the Study of Liver Disease (AASLD) annual meeting.

Gilead's approved combination therapy Harvoni cures 94-99% of hepatitis C genotype 1 patients with eight or 12 weeks of treatment. 

Watch the video below for more on the results of Merck's Hepatitis C study:

From a competitive standpoint, the hurdle for Merck's hepatitis C therapy was to demonstrate that four or six weeks of treatment could match the efficacy of Gilead's eight or 12 week treatment schedule.

On this score, Merck missed. 

Merck's hepatitis C regimen is only disappointing because improvements in treatments for the viral liver disease have progressed at a rapid and remarkable rate. Five years ago, the best treatment for hepatitis C required weekly injections and twice-daily pills for one year. At best, about half of hepatitis C patients were cured but only after enduring debilitating side effects, including flu-like symptoms and anemia.

Three years ago, Vertex Pharmaceuticals(VRTX) - Get Report and Merck were the first companies to introduce new pills which for the first time, blocked enzymes used by the virus to make copies of itself. The addition of these new pills to the old standard of care, reduced treatment time to six months and improved cure rates to 70-80%. 

Today, Gilead's Harvoni is a single pill taken once per day. No injections are required. Almost every hepatitis C patient who takes the pill for eight or 12 weeks will be cured, with negligible side effects. With the bar for new hepatitis C therapies set so high, it becomes difficult for companies like Merck to improve upon already-approved treatments.

The price of hepatitis C treatment might become the next big competitive battleground. Abbvie(ABBV) - Get Report is expected to secure FDA approval for it's own, all-oral treatment regimen before the end of the year. While not as convenient as Gilead'd Harvoni, investors have speculated that Abbvie may price its own hepatitis C therapy at a discount. A lower-priced hepatitis C treatment option might win favor with insurance companies and state Medicaid agencies which have complained Gilead is charging too much. 

In the "C-Swift" study reported Monday, Merck enrolled 102 newly diagnosed patients with genotype 1 hepatitis C. The patients were first segmented by the presence of cirrhosis in their livers, and then randomized to receive four, six, or eight weeks of treatment with a combination of two Merck medicines -- grazoprevir and elbasvir formulated into a single pill -- plus Gilead's Sovaldi. 

Results reported Monday from the C-Swift study were interim in that patients were assessed for sustained viral response -- medical jargon for hepatitis C cure -- at four and eight weeks after treatment stopped. To be deemed fully cured of hepatitis C, patients must have no evidence of virus 12 weeks after treatment. Merck will present final results from the study at a later date, although the cure rates are not expected to change significantly. 

For hepatitis C patients without cirrhosis, six weeks of treatment with Merck's triple-drug regimen led to a cure rate of 87%. The four-week treatment yielded a cure rate of 39%.

For the hepatitis C patients with cirrhosis, the cure rate for eight weeks of treatment was 95%, although that omits two patients who discontinued treatment. Accounting for those two missing patients yielded a cure rate of 86%. The six-week course of treatment yielded a cure rate of 80%. 

Merck believes it has more potent hepatitis C drugs in its pipeline which may lead to higher cure rates. Building on the results from the C-Swift study, Merck will soon begin clinical trials of the grazoprevir-elbasvir pill combined with MK-3682. The latter drug is a potent hepatitis C "nuc" developed by Idenix Pharmaceuticals, which Merck acquired earlier this year for $3.9 billion.

Merck will also study a combination of MK-3682, grazoprevir and an earlier-stage but more potent compound known as MK-8408. Dr. Eliav Barr, Merck's vice president of infectious diseases, is hopeful that this latter "optimized" triple-drug regimen will yield shortest and most effective cure rates across different hepatitis C patient populations.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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