Masitinib
Masitinib is a **protein tyrosine kinase inhibitor** primarily used in veterinary medicine for the treatment of non-resectable mast cell tumours in dogs, particularly those with a confirmed mutated c-KIT receptor. It is also being investigated for use in other inflammatory and neoplastic conditions such as atopic dermatitis, inflammatory bowel disease, osteosarcoma, and haemangiosarcoma. > **Clinical Warning:** Masitinib is a **cytotoxic drug**. Strict safety and handling protocols must be followed by both veterinary staff and pet owners to prevent accidental exposure.
Mechanism: Masitinib acts as a **protein tyrosine kinase (TK) inhibitor**. It selectively and effectively binds with high affinity to mutated forms of the **c-KIT tyrosine kinase receptor**. **c-KIT receptor** → Inhibition blocks the TK receptor pathways that are essential for cell replication, survival, and differentiation, thereby halting tumor growth and progression.
Dosing by species
- Non-resectable mast cell tumours (Patnaik grade 2 or 3) · See Appendix for chemotherapy protocols · PO · unknown · unknown · Preferably with a confirmed mutated c-KIT tyrosine kinase receptor.
- Injection site sarcoma, asthma (investigational) · Limited evidence: administered to healthy cats · PO · unknown · unknown · Not licensed in cats. Further clinical trials required. Monitor closely.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Pregnant or lactating bitches
- Dogs < 24 months old
- Dogs < 7 kg body weight
- Pre-existing signs of myelosuppression
- Previous hypersensitivity to masitinib
Adverse effects
- Diarrhoea (mild to moderate)
- Vomiting (mild to moderate)
- Hair coat changes or alopecia
- Renal toxicity
- Anaemia
- Protein loss (protein-losing nephropathy/enteropathy)
- Myelosuppression
- Increased liver enzyme activity
- Lethargy
- Cough
- Lymphadenomegaly
Drug interactions
- Highly protein-bound drugs · May displace masitinib or be displaced, increasing the risk of adverse side effects · moderate
- Cytochrome P450 inhibitors or inducers · May alter the metabolism of masitinib, increasing the risk of toxicity or reducing efficacy · moderate
Monitoring
- Blood pressure (baseline and monthly)
- Urinalysis (baseline and monthly)
- Haematology (baseline and monthly)
- Biochemistry (baseline and monthly)
- Coagulation profiles (if adverse signs witnessed)
- Faecal occult blood tests (if adverse signs witnessed)
- Weekly owner check-ins for the first 6 weeks to monitor for side effects
Overdose
No specific overdose information is provided in the monograph. > **Clinical Pearl:** Overdose of tyrosine kinase inhibitors typically exacerbates gastrointestinal toxicity (severe vomiting, diarrhea) and myelosuppression. Treatment is symptomatic and supportive. Monitor renal and hepatic parameters closely.
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.