Interferon, part of the standard treatment for hepatitis C, is a major cause of depression in patients with the disease.

A new study has linked the high rate of suicide among hepatitis C patients to side-effects of interferon, which is usually taken together with ribavarin.

These findings will increase clinicians’ interest in alternatives to interferon in the treatment of the life-threatening infectious disease.

Researchers at Loyola University, Chicago, observed: “Depression is a relatively frequent and potentially serious complication of interferon therapy for hepatitis C virus infection.”

Hepatitis C is an increasingly widespread infection worldwide, causing pain, fatigue, disability and death.

The standard treatment is a combination of ribavirin and pegylated interferon. The latter can relieve muscle and joint pain and reduce fatigue.

However, interferon affects serotonin levels and is consequently associated with depression. The study reports that between 10% and 40% of hepatitis C patients receiving interferon experience depression and may be at risk of suicide.

The study authors recommend that patients with a personal or family history of depression or suicide attempts should be carefully assessed and possibly treated for that condition before treatment with interferon begins.

There is conflicting evidence about the effectiveness of antidepressants in patients who are receiving interferon – they may help to reduce the symptoms, but do not seem reliably able to prevent the condition.

Interferon also has flu-like symptoms, and the new study will increase the pressure to develop alternative treatments such as the combination therapy involving drugs from Gilead and BMS that recently demonstrated strong clinical efficacy in a phase II trial.

The combination of two oral drugs from Gilead Sciences and Bristol-Myers Squibb (BMS) has the potential to offer a faster cure for hepatitis C.

Gilead’s GS-7977 and BMS’s daclatasvir, taken daily for six months, cured almost all patients in a phase II clinical trial while sparing them the side-effects of interferon.

However, the lack of a partnership between the two companies could delay patient access to the drug combination.

The companies said that all 88 trial participants who took the two-drug combination had undetectable virus levels after four weeks, and 84 had undetectable virus levels four weeks after the end of the 24-week trial.

The most common side-effects of the combination were fatigue, headache and nausea; the non-ribavirin treatment group also showed low phosphorus and high cholesterol levels.

Gilead also reported two 12-week phase II trials: one where GS-7977 and ribavirin cured 22 of 25 hepatitis C patients (with undetectable virus levels a month after the trial end); and and one where GS-7977, ribavirin and interferon cured 90% of patients.

Hepatitis C is a chronic blood-borne infection than can cause life-threatening liver damage. No complete oral treatment for the infection currently exists.

In 2011, Vertex and Merck introduced oral medications that increased the cure rate from 60% to 80% – but these need to be used alongside alpha interferon, which is injected weekly for up to a year and has flu-like side-effects.

As yet Gilead and BMS have not agreed to collaborate in order to bring the new combination therapy to market.

Dr Douglas J. Manion, a Senior VP at BMS, said the company was “keen” to work with Gilead but the latter was “unwilling to engage in that collaboration.”

Norbert W. Bischofberger, Executive VP for Research and Development at Gilead, said the company wanted to wait for further clinical trial data: “We told them it’s too early to jump wildly into this collaboration.”

In particular, he noted, Gilead wanted to establish whether the combination of GS-7977 with the generic ribavarin would be as clinically effective as using daclatasvir. If so, not only would the combination be cheaper, but Gilead could increase its profits by using its own ribavarin.

Finally, Bischofberger observed that if no collaboration took place, doctors would still be able to use GS-7977 and daclatasvir together.