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Lysine

By Rania Gollakner, BS, DVM, MPH

Medications

What is lysine?

Lysine (brand names: Enisyl-F®, Incremin®, Viralys®, Felisyl®, Optixcare) is an amino acid supplement used to treat clinical signs associated with feline herpes virus infection in cats.

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

How effective is lysine?

Limited studies in client-owned cats have been performed, but there is anecdotal evidence that lysine works to suppress the symptoms of feline herpes virus.

How is lysine given?

Lysine is given by mouth in the form of a powder, crushed tablet, chewable tablet, or paste/gel. Mix the powder in a small amount of food unless otherwise directed.

This medication can take up to a few weeks before full effects are noted, but gradual improvements are usually noticeable after a few days.

What if I miss giving my pet the supplement?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects are uncommon, especially when the supplement is mixed with food. In humans, stomach pain and diarrhea have been reported, but the significance of this in veterinary patients is unknown. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this supplement?

There are no specific contraindications or risk factors for lysine. Use cautiously in pregnant and lactating pets as studies are limited, although use of this supplement is likely safe.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given lysine: arginine or oral calcium supplements.

Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this supplement?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working.

How do I store lysine?

Unless otherwise directed, store the powder at room temperature in a tight container, protected from moisture.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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