Brand Name: Tamiflu  

Available in 30 mg, 45 mg, and 75 mg capsules; oral suspension (liquid)

Background

What a miracle the development of antibiotics truly was! The commercial development of penicillin and the sulfa antibiotic class represented the first readily available medications that could kill the microorganisms responsible for bacterial infections. Since then, a myriad of antibiotics has become available that exploit the biological differences between the host animal and invading organism systems. But none of these medications made any difference to the viruses. 

This is the canine parvovirus. Reprinted with permission by Jean-Yves Sgro. © 1994 JY. Sgro UW-Madison.

A virus is the simplest organism that can technically be called living. Its structure is simple, often just a cluster of DNA inside a protein coat. The virus has no protein metabolism or other systems that a medication might target. A virus simply acts like a syringe attaching to a host cell, injecting its genetic material inside, and tricking the host cell into transcribing this material. In other words, it injects its own DNA into the host cell, attaching its own DNA to the host's DNA. The viral DNA instructs the cell to stop what it is doing and start mass-producing more virus. Soon the host cell becomes a virus factory, replicating thousands of new viral organisms to go forward and infect new cells.

Viruses are responsible for herpes, influenza, HIV, the common cold, and numerous other infections with which we are familiar. It has only been relatively recently that we have had the technology to attack viral biology. Oseltamivir represents such an effort.   

Oseltamivir specifically targets the influenza virus. This virus bears an attachment enzyme on its surface called neuraminidase. This enzyme allows the flu virus to bud from the host cell in which it was created and then happily pass through the mucus of the respiratory tract to any cell in the tract it wishes to infect. Inhibiting neuraminidase effectively locks the new viral organisms within their host cell, imprisoning them so that they cannot infect new cells. The immune system will recognize the infected cell and kill it along with its infective contents. When it comes to the flu, oseltamivir is felt to cut a couple of days out of a sickness period. All this, of course, has virtually nothing to do with pets.

Recently, veterinary interest has turned to oseltamivir in the treatment of canine parvovirus, a life-threatening infection characterized by vomiting and bloody diarrhea. Because the parvovirus does not use neuraminidase in its replication, one might not expect oseltamivir to have value, but it turns out that neuraminidase is an important enzyme used by pathogenic bacteria invading through the protective mucous barrier of the GI tract. This invasion through the mucous barrier is biochemically similar to the budding of virus from the cell membrane, and oseltamivir is able to inhibit it.  Invasion of intestinal bacteria into the bloodstream is an important cause of death in parvoviral infection, and this is where oseltamavir appears to be helpful, though there is still controversy surrounding its use. Using oseltamivir in parvovirus infection has been shown to improve both weight gain, and white blood cell counts in parvo-infected dogs.

How this Medication is Used   

The medication should be obtained as soon as the diagnosis is confirmed.

To assist in treating canine parvovirus infection, oseltamivir is typically given by mouth twice a day for approximately 5 days. The medication should be obtained as soon as the parvovirus diagnosis is confirmed. If a puppy has been exposed to canine parvovirus but is not ill, it may be possible to avoid the clinical disease by giving a course of oseltamivir. Consequently, if the puppy is more than 40 hours into the infection, oseltamivir may not be as helpful in treatment as the damage is already well underway.

If a dose is accidentally skipped, do not double up on the next dose. Simply give the dose when it is remembered and time the next dose accordingly. Tamiflu suspension should be refrigerated and is only good for 10 days after it has been reconstituted. Capsules may be stored at room temperature. 

In recent years, canine influenza infection has become an important infectious disease of dogs in the U.S. At this time, oseltamivir use has been discouraged for this infection for two reasons. First, canine influenza infection is not readily detectable early enough in its course to be vulnerable to oseltamivir. Second, oseltamivir is considered part of the first line of defense in human influenza pandemic, and overuse or inappropriate use could create influenza drug resistance, potentially leading to human influenza death. Oseltamivir is not approved for use in animals.

Side Effects   

In pets, side effects have not been appreciated; however, veterinary experience is limited. The following is taken from human patient information sheets on oseltamivir.

Side effects that you should report to your prescriber or healthcare professional as soon as possible:   

• difficulty breathing or shortness of breath  
• ear ache or infection  
• infection and inflammation of the sinuses (nose) and chest  
• skin rash    

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):   

• coughing  
• diarrhea  
• difficulty sleeping  
• dizziness  
• headache  
• nausea and vomiting  
• nose bleed  

We include this information as general information but if you are using oseltamivir on a pet and think you may be seeing indications of any of the above, report them to your veterinarian.

Interactions with other Drugs   

Oseltamivir can interfere with concurrent influenza vaccinations.

Concerns and Cautions   

The most important caution is to recognize that canine parvovirus is a life-threatening infection for which there is no substitute for hospitalization. You should never attempt to diagnose parvovirus infection on your own nor treat it without veterinary supervision. Puppies that have advanced parvo symptoms (such as septicemia or severe dehydration) may not respond to oseltamivir, or to any treatment for that matter.

Remember, the goal of using oseltamivir is to minimize the amount of virus in the patient so that the immune system will have an easier job eradicating the infected cells.

Reconstituted oseltamivir does not last longer than 10 days and must be disposed of thereafter.

If a patient seems to have an upset stomach on oseltamivir, give the medication with food.

This medication works best early in the course of infection before the patient is already combating large amounts of infectious organisms. If pathogenic bacteria have already invaded, the effectiveness of oseltamavir will be blunted. Animals that have advanced symptoms such as septicemia, severe dehydration, and pneumonia may not respond to oseltamivir.

It is important to remember that human influenza is a significant disease with the potential to cause human death under certain circumstances. Unnecessary use of anti-viral medications leads to resistance within the influenza virus population, so it is important that medications such as oseltamivir not be used for infections that are not life-threatening in nature or that are likely to resolve with routine supportive care.

It is our policy not to give dosing information over the Internet.