Monday, December 12, 2005

Not a walk in the park with Fido

We have our doubts about Tamiflu as the magic bullet for bird flu (actually we don't have doubts; it isn't). However it may be useful in some specific situations. For example, if you have been in close contact with someone who is infectious (e.g., a close family member) or work in a high risk occupation (e.g., health care worker). Some essential personnel may also be put on prophylactic dosage. For current seasonal flu viruses it is quite effective, although whether it will have the same effectiveness for H5N1 is unknown. Some evidence suggests that the current dosage is inadequate for H5N1 and might promote drug resistance. There is still a shortage and if a pandemic occurs soon it almost certainly rationed. Its use therapeutically is more limited, as it must be given soon after onset of symptoms and even then is not a cure but at best only shortens the duration and reduces severity.

Recently WHO and others suggested Roche's recommended dosage schedule (75 mg/day prophylactically and 150 mg/day in divided doses for threatment) may need to be doubled for H5N1 and the Vietnamese, who have seen the most cases, are increasing the duration of treatment from five days to seven:
"The virus is multiplying to higher levels than normal human viruses, therefore it may take more drug to control this higher level of virus,'' said Jennifer McKimm-Breschkin, a virologist at Australia's Commonwealth Science and Industrial Research Organization (CSIRO) in Melbourne.

"Some H5N1-infected patients treated with Tamiflu have had resistant virus emerge during the treatment, hence the theory is that higher doses may prevent resistance emerging,'' McKimm- Breschkin said. (Bloomberg)
Thus assuming the drug will work for this virus (there are arguments to suggest it might and others that it might not), the doubling of recommended dosage essentially cuts the available supply in half. So it is interesting to observe that available supplies are making their way into veterinary practice and being used for dogs.
The same drug has veterinarians buzzing about its use against the newly identified canine influenza and against more threatening diseases such as parvovirus. Vets are offering their findings on their Web sites and swapping Tamiflu anecdotes on the Veterinary Information Network, a members-only site for animal doctors.

Although the prevalence of canine influenza is not yet known, researchers at one university found a 15 percent infection rate among 2,000 symptomatic dogs tested. (Sacramento Bee)
The uncertainties about the efficacy of Tamiflu in human H5N1 are even greater for the H3N8 virus now more prevalent in dogs. Canine influenza is clinically similar to kennel cough (although the vaccine for kennel cough won't protect against influenza, of course). It has about a 5% mortality. Little is known about the pharmacokinetics of the drug in dogs, how long it should be given or whether use in domestic animals might promote viral resistance (although the canine subtype is different than H5N1, so unless there were recombination between N8 and N1 this seems unlikely). But with supplies short for a pandemic, there is concern about whether this is the best use of the available inventory:
"We would hope that vets would follow the recommendations and policy for this drug because they are part of the health care system in society, and it's in their interest to make sure humans have adequate supplies of antiviral drugs," said Dr. Howard Backer, chief of the immunization branch at the state [California] Department of Health Services.
Americans and Europeans are very attached to their dogs. Some people probably lost their lives in Hurricane Katrina because they wouldn't leave their pets. It is a human emotion and no use to express dismay. Having to make a strategic choice between their fellow citizens and their household pets is just another one of the nasty little non-medical surprises this nasty little virus may have in store for us.

If it happens, this won't be a walk in the park. With or without your dog.