A somewhat controversial study has just been published in the Journal of Veterinary Emergency and Critical Care (Savigny et al 2010). The study looked at the use of Tamiflu (oseltamivir) for the treatment of parvovirus infection in dogs. Tamiflu is best known as a potentially important influenza drug in humans. It's a neuraminidase inhibitor that can prevent replication of some viruses, such as influenza. It actually has no effect on parvovirus, but has been used by some veterinarians based on the hypothesis that it can have an effect on bacteria and perhaps prevent secondary bacterial infections, which contribute to the severity of parvoviral disease.
The study examined a relatively small number of dogs (35) with parvovirus infection. Some dogs received Tamiflu along with standard treatments, while the others received a placebo and standard treatments. There was no difference in major outcomes between the two groups, but control dogs lost more weight during treatment.
The study has some weaknesses and doesn't tell us too much, but it's the first objective investigation of this drug in dogs. There was no significant difference in relevant outcomes, but was that because the drug doesn't work, because the dose was too low (as has been suggested by some) or because the study was too small to detect a real difference? That's the big question.
Some veterinarians are completely convinced Tamiflu works for parvovirus infections and disregard any suggestion that it doesn't. Currently, there is no scientific evidence whatsoever supporting its use, and this study doesn't help much one way or the other. There are abundant anecdotes, and it's plausible that this drug could be useful for treating this disease, but there are a few concerns:
- We really don't know whether it works. Continuing to use a treatment in the absence of objective information is not necessarily a good idea.
- We don't know the appropriate dosage and duration of treatment for dogs. We also don't know which animals Tamiflu might or might not help. It is probably most effective (or perhaps only effective) early in disease.
- Tamiflu is an important human influenza drug, and resistance is emerging in influenza. Can we justify using a drug that is a part of pandemic influenza control for the treatment of canine parvovirus, without any evidence that it is effective or needed?
The article's abstract concludes by saying "Based on these results, the true role of oseltamivir in the treatment of parvoviral enteritis remains speculative, although it is believed that further investigation is warranted." Very true.
We need two things:
- Rational discussion about whether use of drugs like this is justifiable in animals.
- Better studies to tell us whether it works, and if so, how to best use it.
If we end up using it, we also need surveillance to make sure routine use of this drug in animals doesn't contribute to resistance in humans. Unfortunately, the Tamiflu debate is too often full of anecdotes and arguments as opposed to logical discussion and sound evidence. Hopefully that won't get in the way of someone doing a more definitive study.