Patients relapse after Gilead hepatitis C treatment

Hopes that a new Gilead Sciences drug could be the solution to a hard-to-treat form of hepatitis C have been hindered, with patients on the drug quickly relapsing after therapy stopped.

GS-7977 was one of the main assets behind Gilead's $10.8bn acquisition of Pharmasset last year, and has been at the forefront of a wave of enthusiasm for new direct-acting antivirals that promise an alternative to interferon-based therapy for the disease.

The latest data reveal that eight patients with hepatitis genotype 1 who were non-responders to prior treatment with pegylated interferon and ribavirin relapsed within four weeks of stopping treatment with GS-7977 plus ribavirin.

Two other patients have not yet relapsed but are still only two weeks from finishing the 12-week therapy regimen.

The results are particularly disappointing because the objective of hepatitis C therapy is generally not to effect a cure - but to drive levels of the virus down to such a level that the infection is effectively eliminated and therapy can stop.

The latest data suggest that continuous treatment with GS-7977 would be needed to sustain this virologic response, or more likely that additional agents will have to be added to the regimen to improve efficacy.

Shares in Gilead closed 14 per cent down on Friday at $47 on the back of the announcement.

"These data answer an important question about the use of GS-7977 and ribavirin for the treatment of genotype 1 null responder patients, suggesting that additional direct acting antivirals may be necessary to effectively treat this patient population," commented Gilead's chief scientific officer Norbert Bischofberger.

Some analysts suggest that the decline in Gilead's share price could be an over-reaction given that there are a number of other oral direct-acting antivirals that could be used to boost the efficacy of GS-7977 in this hard-to-treat population.

The drug may also still prove to be effective in hepatitis C cases which are less resistant to therapy.

Morningstar analysts pointed out that a longer, 24-week regimen with GS-7977 or combination with other antivirals from Gilead's own portfolio - or indeed other companies such as Johnson & Johnson and Bristol-Myers Squibb - could prove effective.

They still give GS-7977 a 75 per cent chance of reaching the market - initially in genotype 2 and 3 hepatitis C - and expect it to capture around 17 per cent of a market worth $22bn by 2020.