Lamivudine
**Lamivudine** (also known as **3TC**) is an antiviral medication primarily used in veterinary medicine for the management of **Feline Immunodeficiency Virus (FIV)**. In asymptomatic cats, it may delay the onset of the clinical phase. In symptomatic cats, it is often used as part of a combination therapy to improve recovery. > **Clinical Warning:** Lamivudine can cause bone marrow suppression; regular hematological monitoring is essential. **Clinical Pearl:** Combining lamivudine with zidovudine (AZT) has been shown to be more effective at reducing viral load and improving CD4/CD8 ratios over a 1-year period than zidovudine monotherapy.
Mechanism: Lamivudine is a **nucleoside reverse transcriptase inhibitor (NRTI)**. It acts as an analogue of cytidine. Once phosphorylated to its active triphosphate form intracellularly, it competes with natural substrates and incorporates into viral DNA. This causes **chain termination** → inhibits the **viral reverse transcriptase** enzyme → prevents viral replication.
Dosing by species
- Treatment of FIV-positive cats · 25 mg/kg · PO · q12h · May be combined with zidovudine for enhanced efficacy.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Anaemia
- Pre-existing severe bone marrow suppression
Adverse effects
- Cytopenias (predicted)
- Anaemia
- Leukopenia
Drug interactions
- Zidovudine · Synergistic therapeutic effect; more effective at reducing viral load and increasing CD4/CD8 ratios than zidovudine alone.
Monitoring
- Complete Blood Count (CBC) regularly to monitor for cytopenias
- CD4/CD8 ratios
- Viral load
Overdose
Information on overdosage in veterinary species is limited. Overdose is likely to exacerbate hematological toxicities such as **severe cytopenias** (anemia, leukopenia). Treatment should be supportive and symptomatic.
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.