Brand Name: Tamiflu® 

Available in 30 mg, 45 mg, and 75 mg capsules; oral suspension (liquid; 6 mg/ml when reconstituted as directed)

Oseltamivir is an antiviral drug used to treat infections caused by influenza viruses.

Viruses Must Infect a Host Cell to Live and Reproduce. 

Replication will continue until the cell is full. The viruses must then escape the cell so that nearby uninfected cells can be infected. When a sufficient number of cells are dead or dysfunctional, the host becomes ill. 

Most antiviral drugs work by slowing down the virus’s ability to replicate inside the host cell. They generally do this by blocking a protein necessary for the virus to enter, replicate within, or leave the host cell. Not all antiviral drugs work against all classes of viruses. Often, they target a protein that is found only in one class of viruses. This is the case for oseltamivir.

Oseltamivir for the Treatment of Viral Infections in Animals 

Oseltamivir is approved for use in humans to prevent and treat infections caused by the influenza virus, commonly referred to as the flu. It targets a specific enzyme called neuraminidase, which helps the newly formed virus escape from the host cell.

Because the virus cannot escape, it will be trapped in the host cell. Eventually, the host immune system will recognize the infected cell and destroy it.

Of all the viruses infecting humans or animals, only the influenza virus has the neuraminidase enzyme that oseltamivir targets. Because of this, oseltamivir will not inhibit viruses in other classes.

The use of oseltamivir for treating influenza in animals has not been studied.

In some cases of canine parvovirus, oseltamivir has been considered as a treatment. Because parvovirus is not an influenza virus, parvovirus does not have the neuraminidase enzyme targeted by oseltamivir. Oseltamivir will not inhibit parvovirus, and studies do not support its use for inhibiting parvovirus or preventing parvovirus infection.  

One study has reported on the use of oseltamivir (Tamiflu®) in dogs with parvovirus. In this study, 100% of dogs receiving oseltamivir survived. However, 81% of the dogs that did not receive oseltamivir also survived. The hospital stay was not shorter in treated dogs; however, some clinical signs were less severe in some of the oseltamivir-treated dogs. This study did not clearly show a positive effect of oseltamivir in dogs with parvovirus. 

However, if it does help treat parvovirus, it may work by decreasing the effect of gastrointestinal bacteria in the bloodstream (sepsis).

The use of oseltamivir in animals increases its presence in the environment. It has been detected in water. Exposure to even low levels of environmental oseltamivir helps the influenza virus become resistant to its antiviral effects. This has already been demonstrated in wild birds, such as the mallard duck, which serves as a natural reservoir for the influenza virus. This may decrease the drug's effectiveness for treating the human flu. Because of this, the use of oseltamivir in animals is controversial.

Side Effects   

Because oseltamivir has not been studied in dogs or cats, side effects cannot be identified. In humans, nausea, vomiting, and headaches are the most common side effects.

Interactions with Other Drugs   

Because it inhibits influenza viral replication, oseltamivir can interfere with the effectiveness of intranasal influenza vaccinations in humans. It does not interfere with the injectable vaccine. The effect of oseltamivir on influenza vaccinations in dogs has not been studied.

Concerns and Cautions   

Human flu, caused by the influenza virus, is a significant disease causing illness and, in some instances, death. Most drugs that target infectious agents promote the development of resistance in that agent to the specific drug. This is also true for antiviral drugs.

Unnecessary or unwarranted use of an anti-viral medication increases the risk of resistance.  Because of this, oseltamivir should only be used in the instance of life-threatening infections and only if there is a reasonable expectation that it will help in the treatment of the viral disease in your pet.