Doctors struggling to cure patients with C. difficile diarrhea have a new weapon in their armoury.

A new antibiotic specifically developed to treat C. difficile infections has been approved for the Canadian market, the drug's maker, Optimer Pharmaceuticals Canada, announced Thursday.

The drug, to be sold under the brand name Dificid, has an advantage over the existing drug of choice. It has been shown to cut the risk of recurrent bouts of diarrhea in some people suffering from C. difficile.

In fact, a clinical trial done in Canada showed that about 15 per cent of people on fidaxomicin (the drug's generic name) had a relapse, as compared with 25 per cent among people given the standard treatment, an antibiotic called vancomycin.

But fidaxomicin's price tag, a whopping $2,200 for a 10-day course of treatment, means it will probably have a battle on its hands to supplant vancomycin as the treatment option doctors reach for first.

"If the cost were equivalent, I think it would be a no-brainer. We would all be considering this as first-line therapy," said Dr. Andrew Simor, head of microbiology at Toronto's Sunnybrook Health Sciences Centre and an expert on C. difficile.

Simor disclosed that he had served as a member of an advisory board for Optimer on fidaxomicin.

"[But] given the cost, that's going to be a challenge. And certainly I wouldn't see it as first-line therapy at this cost because it's hard to justify."

Vancomycin costs somewhere between $150 and $300 for a 10-day course of therapy.

More and better drugs for C. difficile diarrhea are badly needed. While most patients who contract the infection are cured with a course of antibiotics, between 20 per cent and 30 per cent of patients will suffer a recurrence.

In a portion of those patients, the infection will resist repeated courses of antibiotics, leaving patients frantic and their doctors desperate to find ways to cure a condition that can tether people suffering from it to their bathrooms.

Often those recurrent cases are caused by a virulent strain of the bacterium that has been circulating over the past decade or so, the so-called NAP-1 strain. It is also sometimes referred to as the 027 strain.

But Dificid doesn't appear to be as successful at reducing the risk of relapses with cases caused by the NAP-1 strain as it is with other C. difficile strains.

In the Canadian study, led by Calgary researcher Dr. Tom Louie, fidaxomicin was as effective as vancomycin in treating NAP-1 cases. But the rate of recurrence was similar between the two drugs for these cases, according to the trial, which was published last year in the New England Journal of Medicine.

Dr. Christine Lee, an infectious diseases specialist from St. Joseph's Health Care in Hamilton, said she believes the drug will be particularly useful in patients at high risk of having recurrent bouts of C. difficile — people over the age of 65, those with suppressed immune systems, and others with known risk factors.

But Lee — who was involved in clinical trials of the drug and agreed to speak about it for Optimer — was cautious not to over hype the role the drug will play in the care of C. difficile patients.

"I think it is promising but we don't know until the medication is marketed and widely used," she said in an interview.

Among other things, Lee noted the organism can change — as it did with the emergence of the NAP-1 strain — and that might have an impact on the efficacy of the drug.

"We have to be a little cautious," she said. "The key message is prevention — to prevent as many cases from happening in the first place."

Simor agreed preventing cases needs to be the goal. But he said it's good to have an alternative treatment.

"Our current treatment options are limited and less than ideal. This is not the final answer, because it's not a perfect drug, but it does offer another very valuable treatment option. And that's going to be hugely important."