Primaquine
Primaquine phosphate
Also known as: Generic (Sanofi Winthrop) · primachina · primachinum · primaquina · SN 13272
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Babesia felis | 0.5 mg (as base)/kg PO once daily | PO | q24h | 1-3 days | 🌎 NA |
| 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 | 🌎 NA |
| Babesia felis | Primaquine phosphate 1 mg/kg IM one time | IM | once | 1 time | 🌎 NA |
- Babesia felis: Dose is for primaquine base.
- Babesia felis: The drug does not sterilize the infection.
- Babesia felis: 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.
Overview
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 of action
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.
Safety & warnings
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
Precautions
WARNING: Primaquine has an extremely narrow therapeutic index in cats.
- Dosing Confusion: Commercially available human tablets are usually too concentrated for domestic cats. A specialized compounding pharmacy is highly recommended. Prescribers must be explicitly clear whether the dose is based on primaquine base or primaquine phosphate (26.3 mg primaquine phosphate = 15 mg primaquine base).
- G-6-PD Deficiency: Contraindicated in humans (and theoretically animals) with Glucose-6-Phosphate Dehydrogenase deficiency due to severe risk of hemolytic anemia.
- Avoid use during pregnancy and lactation due to the risk of hemolytic anemia in fetuses/nursing neonates.
Drug interactions
May potentiate the toxicity of one another; use of primaquine within 3 months of quinacrine is not recommended.
Concurrent use may cause an increased risk for toxicity and severe myelosuppression.
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
Pharmacokinetics
Absorption
No pharmacokinetic information located for small animals. In humans, it is rapidly absorbed with high (96%) systemic bioavailability.
Distribution
Extensively distributed (human data).
Metabolism
Rapidly metabolized in the liver to carboxyprimaquine. It is unknown if this metabolite possesses antiprotozoal activity.
Elimination
Elimination half-life is around 6 hours for primaquine; 24 hours for carboxyprimaquine (human data).
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.
Available products
Formulations
- Oral tablets
- Compounded oral suspensions
- Compounded IM injection
Human-labeled
- Primaquine Phosphate Oral Tablets: 26.3 mg (equivalent to 15 mg primaquine base)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Primaquine phosphate tablets should be stored in a tight, light-resistant container below 40°C, preferably between 15-30°C.
Client information
- Strict Dosing: This medication has a very low safety margin when used in cats. Exact adherence to the prescribed dosage is extremely important. Never double-up the next dose if a dose was previously missed.
- Administration: Give the dose with food to reduce the chance of gastrointestinal problems, particularly vomiting.
- Monitoring: Watch your pet closely for signs of lethargy, pale or discolored gums, or breathing difficulties, and report any abnormalities to your veterinarian 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.