Tiny biotech stock Achillion Pharmaceuticals (NASDAQ: ACHN  ) reported what could be pretty big news for hepatitis C patients this week. The clinical stage biotechnology company released data showing that combining its ACH-3102 with Gilead Sciences' (NASDAQ: GILD  ) Sovaldi achieved 100% cure rates in as little as six weeks of treatment. The success of that combination is prompting Achillion to launch a study of the two drugs over an even shorter 4-week dosing period. If that study pans out, it could be the biggest advance in hepatitis C treatment since Sovaldi won approval in 2013.

Source: Achillion Pharmaceuticals

Blockbuster breakthrough
A decade ago, hepatitis C patients were treated with a combination of the drugs peg-interferon and ribavirin, which was dosed over 48 weeks, cured just 50% of patients, and came with a host of side effects. In 2011, treatment took a huge step forward when the FDA approved Vertex Pharmaceuticals' Incivek, a therapy that cured 80% of patients over a 24 week time period.

However, Incivek was still far from a perfect drug. It was injected, rather than taken as a pill. Additionally, Incivek was still dosed alongside the pesky and side effect-causing peg interferon and ribavirin mashup, a fact that hampered adherence rates.

As a result, the approval of Gilead Sciences' oral Sovaldi for the treatment of hepatitis C has arguably been the biggest leap forward in treatment for the disease. Sovaldi's once-daily oral dosing, 12-week treatment regimen, and 90% plus cure rates made a functional hepatitis C cure available to the vast majority of patients for the first time. Importantly, it did so while removing the need to dose peg interferon simultaneously in many patients. As a result, Sovaldi became the fastest drug to ever reach billion dollar blockbuster status, and the only drug to achieve $10 billion in sales during its first year on the market.

Improving adherence rates
Although Sovaldi was a breakthrough for patients, considerable room remains to improve hepatitis C treatment. Sovaldi still requires the dosing of ribavirin in many patients, and a 12-week treatment course still creates obstacles that can impact patient adherence rates, which in turn can significantly increase costs and reduce efficacy.

To address some of that problem, Gilead Sciences won approval of a single dose combination tablet of Sovaldi and ledipasvir, sold as Harvoni, in October of 2014. Harvoni casts aside peg interferon and ribavirin for the vast majority of patients, offers cure rates in the high 90% range, and can be dosed over as little as an 8-week period for roughly 45% of genotype 1 patients.

Removing the need to dose peg interferon and ribavirin, and shortening treatment periods by a third, means that Harvoni is a big improvement over Sovaldi in type 1 patients. But an even better solution could be coming from Achillion Pharmaceuticals.

Source: Achillion Pharmaceuticals

Shorter durations
With current treatments cure rates at the mid to high 90% levels, the next major advance in treatment could be delivering similarly effective treatments with far fewer doses.

A number of companies, including Gilead Sciences and Merck & Company, are developing shorter-duration treatments for hepatitis C, but it's Achillion that has reported the steadiest stream of recent success.

In November, Achillion announced that combining ACH-3102, a drug targeting the same protein as Gilead Sciences' ledipasvir, when dosed alongside Sovaldi for eight weeks successfully cleared the disease in 100% of the genotype 1 patients studied. That prompted Achillion to launch a study to evaluate treatment over a shorter six week period.

In late December, Achillion reported interim results from that six week study suggesting that matching up ACH-3102 with Sovaldi was equally effective in the shorter period. In February, Achillion released the full results from that six week trial, which showed that 100% of genotype 1 patients were indeed disease-free 12 weeks following treatment ending.

Now with success in both an eight week and a six week study, the company is launching another study that will evaluate the combination's efficacy over an even shorter four week treatment duration.

Looking ahead
Currently, Harvoni's eight week regimen is only available to genotype 1 patients who have a viral load that is below 6 million IU/ml. That means that the majority of patients are still being dosed with 12 weeks of Harvoni, and that there could be a compelling argument made that a shorter therapy could win over a significant share of the hepatitis C drug market; particularly given that Achillion's trial included patients with viral loads above that 6 million IU/ml level.

A six week therapy may or may not be a big enough differentiator to encourage the eventual use of Achillion's drug over other therapies. However, a four week regimen would clearly be a major advance, and that could mean that investors would be wise to keep an eye on this company over the coming months.