Shares of Gilead Sciences (NASDAQ:GILD) got knocked down last week after CVS Health (NYSE:CVS) released data showing higher discontinuation rates for hepatitis C patients taking Sovaldi than Gilead Sciences saw in its clinical trials.

Sovaldi

Source: Gilead Sciences

On one hand, discontinuations are clearly bad news for Gilead Sciences. If patients aren't taking Sovaldi for 12 weeks, Gilead Sciences isn't getting the full $84,000 for the full course of treatment.

But a higher discontinuation rate isn't really all that surprising. It stands to reason that if you're willing to be a guinea pig for an unapproved medication, you're more dedicated to ridding yourself of the virus than the average infected hepatitis C user. Increasing discontinuation rates from around 2% seen in clinical trials to 8.7% in real life is somewhat to be expected.

And with all of that negativity, there's a surprising silver lining in CVS's data.

Different courses
Sovaldi can be taken with interferon and ribavirin, only ribavirin, or off-label with Johnson & Johnson's (NYSE:JNJ) Olysio. CVS found the discontinuation rates were wildly different with 10.2% of patients taking Sovaldi with interferon and ribavirin discontinuing treatment, but just 4.2% of patients taking Sovaldi with Olysio discontinuing treatment. Sovaldi plus just ribavirin came in between the two at 9%.

Interferons -- Roche's Pegasys or Merck's (NYSE:MRK) PegIntron -- have nasty side effects that makes patients feel like they have the flu. A whopping 11% of hepatitis C patients taking Pegasys in clinical trials stopped taking the drug. Of course those patients knew they'd have to be on Pegasys for almost a year, so their tolerance for side effects was understandably lower than clinical-trial patients taking Sovladi and interferon scheduled for just three months of treatment.

Gilead has its own Sovaldi cocktail drug under Food and Drug Administration review that doesn't require interferon. It seems reasonable to assume that the interferon-free combination is likely to have a low discontinuation rate close to the 4.2% that CVS saw with Sovaldi-Olysio. So the report very much seems to validate CVS' decision to push forward into the all-oral combination.

Competition
Making the drugs easy to take -- whether that's through less severe side effects or by making the regimen more convenient -- should encourage doctors to prescribe the drugs since discontinuations hamper the likelihood of a cure.

The convenience factor could be a detriment to Abbvie (NYSE:ABBV), which will have its own hepatitis C combo approved around the same time Gilead Sciences' Sovaldi combination is approved, but Abbvie's regimen isn't as convenient because it requires more pills.

Only time will tell how much convenience is a factor in doctors' prescription habits for hepatitis C regimens, but it should be noted that for HIV -- where medication adherence is critical -- all-in-one HIV regimens have become the mainstay treatments.

Insurance companies may even be willing to pay more for hepatitis C drugs with a lower discontinuation rate. Discontinuations are an issue for insurance companies because they're wasting money if the patients aren't cured with the partial treatment. The patients will have to be treated later on with a full course and could develop resistance to the drugs making them harder to treat.

The next obvious move to increasing adherence further is to shorten the treatment duration. Whether it's side effects or a lack of motivation to stay on the drugs, if a treatment was effective after just one or two months, patients should be more willing to stay on the medication for the entire treatment regimen.

Bristol-Myers Squibb (NYSE:BMY) is testing a combination of Sovaldi with two of its hepatitis C drugs to see if four weeks is sufficient to rid patients of the virus. And Merck, which is late to the cocktail-treatment party, recently purchased Idenix Pharmaceuticals in hopes that combining Idenix's drugs with its own could decrease the treatment time.

Sovaldi is clearly the dominant player and I'm not sure the CVS report is going to change that much in the short term. In the long term, it underlines the importance of discontinuation rates and stresses where competition might find a niche to break into the hepatitis C market.

Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends CVS Health, Gilead Sciences, and Johnson & Johnson. The Motley Fool owns shares of Gilead Sciences and Johnson & Johnson. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.