OSELTAMIVIR - Mar Vista Animal Medical Center

OSELTAMIVIR

(for veterinary information only)

BRAND NAME: TAMIFLU

AVAILABLE IN
30 mg, 45 mg and 75 mg CAPSULES
or
ORAL SUSPENSION

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 have become available exploiting the biological differences between host animal and invading organism systems. But none of these medications made any difference to the viruses.

A virus is the simplest organism that can technically be called “living.” Its structure is very 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.

This is the actual canine parvovirus

This is the actual canine parvovirus
(image by JY Sgro, UW-Madison)

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 a special 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. Oseltamivir is felt to cut a couple of days out of one’s sickness period when it comes to the flu.

All this, of course, has virtually nothing to do with pets.

Tamiflu

(original graphic by marvistavet.com)

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. Use of oseltamivir in parvovirus infection has shown to improve both weight gain and white blood cell counts in parvo infected dogs.

HOW THIS MEDICATION IS USED

To assist in the treatment of canine parvovirus infection, oseltamivir is typically given orally 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 circumvent the clinical disease by giving a course of oseltamivir. Usually an oral suspension is compounded or the human product is given.

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 Canine influenza infection has become an important infectious disease of dogs in the U.S. At the present 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 administration.

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. One should never attempt to diagnose parvovirus infection on one's 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). 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..

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, this effect can be mitigated by giving the medication with food.

It is important to remember that human influenza is a significant disease with 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 which are not life-threatening in nature or which are likely to resolve with routine supportive care.

For more details on canine parvovirus, see the Parvovirus Information Center on this site.

Short version (to help us comply with "Lizzie's Law")

Page last updated: 9/4/2020