Feline Viral Rhinotracheitis (FVR) Treatment with L-Lysine

L-Lysine is an essential amino acid that may be used to help manage Feline Viral Rhinotracheitis, or FVR. Also known as feline influenza or cat flu, this widespread and highly contagious infection affects the feline upper respiratory system. Cats suffering the effects of the airborne FHV-1 virus may experience a host of uncomfortable and harmful symptoms, like sneezing, watery eyes and nasal discharge. Vaccines are available that may reduce the effects of the virus, however, it may not necessarily prevent a cat from becoming infected with FVR.

For owners of cats with FVR, the outbreak and effects of the virus may seem difficult to control. A growing number of animal medical professionals recommend L-Lysine supplements to help suppress the growth of FHV-1 in felines. Learning how this common supplement works, including recommendations and precautions regarding its use, may provide owners with a relatively affordable and accessible way to manage FVR in their pets.

What Is L-Lysine?

L-Lysine, or Lysine, is of one of several protein molecules, or protein building blocks, that are crucial for healthy function in humans, felines and other animals. Although they play an important role in proper physical development, essential amino acids like L-Lysine do not occur naturally in animals. They must be obtained through food and sometimes supplements. L-Lysine is key to growth and helps convert fatty acid into energy by contributing to the production of carnitine. This amino acid is also thought to be an important part of calcium absorption, as well as bone, cartilage and tendon formation.

How Does It Help Treat FVR?

Many animal care experts believe that concentrated amounts of L-Lysine may help suppress the growth of the herpesvirus responsible for FVR. This is due to the inhibiting effect L-Lysine has on the amino acid Arginine, which is required for virus like FHV-1 to reproduce. The two amino acids are thought to have competing effects, so increasing the amount of L-Lysine may help reduce the presence of Arginine in cats infected with FVR. Lower levels of Arginine in the system may then slow the growth of the herepes virus and reduce uncomfortable symptoms in an affected animal.

Guidelines for L-Lysine Use

As with any supplement, cat owners should consult with their veterinarian or other animal care expert before giving their cats L-Lysine. Although the supplement is believed to be generally safe for use in most cats with FVR, a trusted professional who is familiar with an individual animal's medical history and physical condition may have suggestions for specific L-Lysine dosages and formulas. 

There are many varieties of L-Lysine supplements available, including products designed for general use in people and those targeting cats. Human-grade L-Lysine supplements are sometimes preferred over feline varieties because they tend to be cheaper and more readily available. With this option, owners may want to avoid products containing propylene glycol. This compound solvent, used in a number of household and pharmaceutical products, has been associated with anemia in cats.

Some of the most common forms of L-Lysine supplements available for feline oral use include:

  • Pressed tablets (available as L-Lysine or Lysine in many drugstores and other retailers).
  • Flavored paste designed for cats (sold as Enisyl-F by veterinary pharmaceutical company Vetoquinol).
  • Flavored chew treats (sold as Enisyl-F by Vetoquinol and Vetri-Lysine by Vetri-Science Laboratories).