Quinacrine
Quinacrine HCl
Also known as: Mepacrine HCl
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
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Giardia or other susceptible protozoa (second-choice) | 6.6 mg/kg PO q12h | PO | q12h | 5 days | 🌎 NA |
| Giardia or other susceptible protozoa (second-choice) | 9 mg/kg PO q24h | PO | q24h | 6 days | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Giardia | 9 mg/kg PO once daily | PO | q24h | 6 days | 🌎 NA |
| Coccidiosis | 10 mg/kg PO once daily | PO | q24h | 5 days | 🌎 NA |
| Giardia | 11 mg/kg PO q24h | PO | q24h | 12 days | 🌎 NA |
| Coccidiosis | 10 mg/kg PO once daily | PO | q24h | 5 days | 🌎 NA |
Reptiles
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hemoprotozoal infections | 19-100 mg/kg PO q48h (every other day) | PO | q48h | 2-3 weeks | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Quinacrine is a synthetic acridine derivative primarily used as an antiprotozoal and anthelmintic agent.
Historically, it was utilized for the treatment of Giardia, Leishmania, and coccidia infections. However, its use in modern veterinary medicine has largely been superseded by safer and more effective alternatives (such as metronidazole or fenbendazole for giardiasis).
Clinical Pearls:
- May improve clinical signs of giardial infection but often fails to completely eliminate the organism.
- Can cause a harmless yellow discoloration of the skin and urine, which should not be confused with icterus/jaundice.
- Commercial availability is currently a significant issue; it typically must be compounded.
- Considered a potential teratogen and should be avoided in pregnant animals unless absolutely necessary.
Mechanism of action
The exact antiprotozoal mechanism against Giardia is not fully elucidated, but it involves multiple pathways:
- DNA Intercalation: Binds to DNA by inserting itself between adjacent base pairs → inhibits RNA transcription and translocation.
- Metabolic Inhibition: Interferes with electron transport and inhibits succinate oxidation.
- Enzyme Inhibition: Inhibits cholinesterase.
- In humans, it binds to nucleoproteins to suppress lupus erythematosus (LE) cell factor.
Safety & warnings
Contraindications
- Hepatic dysfunction (relative)
- Pregnancy (relative, potential teratogen)
- Psychotic disorders (in humans)
- Psoriasis (in humans)
- Porphyria (in humans)
Adverse effects
- Yellowing of skin and urine (benign)
- Anorexia
- Nausea and vomiting
- Diarrhea
- Abnormal behaviors ('fly biting', agitation)
- Lethargy
- Pruritus
- Fever
- Hypersensitivity reactions (rare)
- Hepatopathy (rare)
- Aplastic anemia (rare)
- Corneal edema (rare)
- Retinopathy (rare)
Precautions
Hepatic Impairment: Use with extreme caution in patients with hepatic dysfunction, as the drug concentrates heavily in the liver. Pregnancy: FDA Category C. Has caused fetal death in rats at high doses and is implicated in human birth defects. Weigh risks vs. benefits. Laboratory Interference: Can cause falsely elevated plasma and urine cortisol values due to interfering fluorescence.
Drug interactions
May cause a 'disulfiram-like' reaction if used concurrently.
Quinacrine concentrates in the liver; use with caution with other hepatotoxic agents.
Quinacrine increases the toxicity of primaquine; do not use simultaneously.
Monitoring
- Efficacy (fecal exams, reduction in diarrhea)
- Adverse effects (GI upset, behavioral changes)
Pharmacokinetics
Absorption
Absorbed well from the GI tract or after intrapleural administration.
Distribution
Distributed throughout the body, but CSF levels are only 15% of plasma levels. Concentrates in the liver, spleen, lungs, and adrenals. Highly bound to plasma proteins in humans (80-90%). Crosses the placenta.
Metabolism
Slowly metabolized.
Elimination
Eliminated very slowly, primarily by the kidneys. Acidifying the urine increases renal excretion. Detectable in urine up to 2 months after discontinuation.
Overdose
Acute Toxicity: Overdosage can be severe and potentially fatal.
- Clinical Signs: CNS excitation (including seizures), severe GI disturbances, vascular collapse, and cardiac arrhythmias.
- Treatment:
- Gut emptying protocols (emesis/lavage, activated charcoal).
- Supportive and symptomatic therapies.
- Urinary acidification (e.g., with ammonium chloride) and forced diuresis with adequate fluid therapy to enhance renal excretion.
Available products
Formulations
- Tablets (Compounded)
- Oral liquid (Compounded)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets in tight, light-resistant containers at room temperature. Not stable in solution for any length of time, but tablets may be crushed and mixed with food to mask the bitter taste immediately before administration.
Client information
- Administration: Give this medication after meals to reduce stomach upset. Ensure your pet has plenty of water available.
- Discoloration: You may notice your pet's skin or urine turning a yellow color. This is a harmless side effect of the drug and does not mean your pet has jaundice or liver disease.
- Side Effects: Watch for vomiting, diarrhea, lethargy, or unusual behaviors (like snapping at the air, known as 'fly biting'). Contact your veterinarian if these occur.
- Compliance: It is crucial to finish the entire prescribed course, even if your pet seems better.
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.