Primaquine
Primaquine is an 8-aminoquinoline **antiprotozoal** agent primarily utilized in veterinary medicine as the drug of choice for treating ***Babesia felis*** in cats. - **Clinical Pearl**: While highly effective at managing clinical signs, it typically does not achieve complete parasitological cure (sterilization of the infection), and relapses may occur requiring repeated courses of therapy. - It also has potential utility against ***Hepatozoon canis*** in dogs and ***Plasmodium spp.*** (avian malaria) in birds. - **Caution**: Primaquine has an exceptionally narrow therapeutic index (safety margin) in felines, necessitating extreme precision in dosing.
Mechanism: The exact antiprotozoal mechanism of action is not fully elucidated. - It is believed to **bind and alter protozoal DNA**. - **Pharmacological Pearl**: As an 8-aminoquinoline, it likely interferes with the parasite's mitochondrial function. It generates **reactive oxygen species (ROS)** → disrupts electron transport → causes severe cellular and oxidative damage to the protozoa.
Dosing by species
- Babesia felis · 0.5 mg (as base)/kg PO once daily · PO · q24h · 1-3 days · Dose is for primaquine base.
- Babesia felis · 1 mg (total dose per cat) primaquine phosphate PO every 36 hours for 4 treatments, then 1 mg (total dose) per cat every 7 days for 4 treatments · PO · q36h then q7d · 4 treatments each · The drug does not sterilize the infection.
- Babesia felis · Primaquine phosphate 1 mg/kg IM one time · IM · once · 1 time · IM dosage form must be compounded.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Known hypersensitivity to primaquine
- Concurrent use of bone marrow suppressant medications
- Patients susceptible to granulocytopenia (e.g., lupus, rheumatoid arthritis)
- Glucose-6-Phosphate Dehydrogenase (G-6-PD) deficiency
- Pregnancy
- Lactation
Adverse effects
- Vomiting (most common in cats)
- Nausea
- Myelosuppression
- Methemoglobinemia
- Hemolysis
Drug interactions
- Quinacrine · May potentiate the toxicity of one another; use of primaquine within 3 months of quinacrine is not recommended.
- Bone Marrow Depressants (e.g., amphotericin B, azathioprine, chloramphenicol, antineoplastics) · Concurrent use may cause an increased risk for toxicity and severe myelosuppression.
- Hemolytic Drugs (e.g., acetohydroxamic acid, sulfonylureas, quinidine, sulfonamides) · Concurrent use may cause an increased risk for toxicity and hemolysis.
Monitoring
- CBC (mandatory, monitor weekly while treating)
- Improved clinical signs (increased appetite and body weight)
- Improvement in anemia
Overdose
> **CRITICAL**: In cats, dosages **greater than 1 mg/kg** can be lethal. - **Management**: Overdoses should initially be handled aggressively using standardized protocols for removal of the drug from the gut (emesis, activated charcoal) to prevent absorption. - Provide intensive supportive care for potential methemoglobinemia, hemolysis, and myelosuppression. - Because of the potential seriousness of overdoses, it is strongly recommended to contact an animal poison control center for guidance immediately.
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.