Lysine
Lysine is a nutritional amino acid traditionally used in veterinary medicine with the intent of suppressing **Feline Herpesvirus-1 (FHV-1)** infections in cats. > **Clinical Controversy**: While historically popular, recent robust studies have cast significant doubt on its efficacy. Research indicates that lysine supplementation does not prevent or reduce the recurrence of upper respiratory tract infections in shelter cats. In some studies, cats receiving lysine actually showed an *increase* in disease severity and FHV-1 DNA detection. Consequently, many veterinary ophthalmologists and infectious disease experts no longer recommend its routine use.
Mechanism: Lysine is an amino acid that acts as a competitive antagonist to **arginine** during viral replication. * **Mechanism**: Herpesviruses require arginine to synthesize viral proteins and produce infective viral particles. * **Pathway**: Lysine competes with arginine → Lysine is erroneously incorporated into the viral structure instead of arginine → The resulting viral particles are defective and less infective. *Note: The clinical failure of this mechanism in cats may be due to the feline's strict dietary requirement for arginine; artificially lowering arginine activity via lysine supplementation can have detrimental systemic effects.*
Dosing by species
- To prevent or reduce recurrent feline herpesvirus ocular infections · 500 mg PO twice daily for life · PO · q12h · for life
- To prevent or reduce recurrent feline herpesvirus ocular infections · 500 mg mixed with food daily · PO · q24h
- To prevent or reduce recurrent feline herpesvirus ocular infections · 250 mg PO twice daily · PO · q12h
- As adjunctive therapy for feline herpesvirus dermatologic infections · 250 mg PO twice daily · PO · q12h
- As adjunctive therapy for feline herpesvirus dermatologic infections · 250 mg PO once to twice daily · PO · q12h-q24h
- Feline herpesvirus-1 (FHV-1) infection management · 500 mg · PO · q12-24h · Adults. Equivalent to 2 ml/2 pumps q12h.
- Feline herpesvirus-1 (FHV-1) infection management · 250 mg · PO · q12-24h · Kittens. Equivalent to 1 ml/1 pump q12h.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- No specific contraindications noted
- Preparations containing propylene glycol (toxic to cats)
Adverse effects
- Abdominal pain
- Diarrhea
- Nausea
- Vomiting
- Diarrhoea (mild, reversible)
Drug interactions
- Arginine · May negate the anti-herpesvirus effects of lysine
- Calcium (oral) · Concomitant use may increase calcium absorption from the gut and decrease calcium loss in the urine
Monitoring
- Clinical signs of herpesvirus infection (ocular and respiratory symptoms)
- Clinical signs of FHV-1 (ocular and respiratory signs)
- Gastrointestinal tolerance (monitoring for diarrhoea)
Overdose
Significant toxicity is highly unlikely. * **Clinical Signs**: Mild gastrointestinal effects such as **nausea, vomiting, and diarrhea** may occur with massive ingestions. * **Management**: Supportive care as needed; usually self-limiting.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.