Levamisole Hydrochloride — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	5-10 mg/kg	Once daily	Duration: 2-3 days for roundworms/hookworms; 5-7 days for lungworms Notes: For heartworm microfilariae: 5-10 mg/kg once daily for 6-10 days. Administer on an empty stomach for optimal absorption.
Cat	PO	5-10 mg/kg	Once daily	Duration: 2-3 days for roundworms/hookworms; 5-7 days for lungworms Notes: Use with caution in cats; narrow margin of safety. Administer with food to reduce GI upset.
Horse	PO	5-10 mg/kg	Once	Duration: Single dose Notes: May be repeated in 2-4 weeks for severe infections. Administer via stomach tube or as a paste.
Cattle	SC	5-7.5 mg/kg	Once	Duration: Single dose Notes: Injectable formulation is commonly used. For oral drench: 7.5 mg/kg. Withdrawal times must be observed.
Sheep/Goats	PO	7.5-12 mg/kg	Once	Duration: Single dose Notes: Oral drench or injectable (SC) at 7.5 mg/kg. Goats may require higher doses due to metabolism.
Rabbit	PO	10-20 mg/kg	Once daily	Duration: 3-5 days Notes: Use with caution; safety in rabbits is not well established. Monitor for adverse effects.
Poultry	PO	20-40 mg/kg	Once	Duration: Single dose Notes: Administer in drinking water or feed. Ensure adequate intake.
Reptiles	PO	5-10 mg/kg	Once daily	Duration: 3-5 days Notes: Dose based on limited studies; adjust based on species and severity.

Clinical Indications & Species Uses

General Indications

Treatment of susceptible nematode infections in various species

Dog (Canine)

Treatment of roundworms (Toxocara canis, Toxascaris leonina)
Treatment of hookworms (Ancylostoma caninum, Uncinaria stenocephala)
Treatment of lungworms (Filaroides osleri, Oslerus osleri)
Treatment of heartworm microfilariae (Dirofilaria immitis) (as adjunctive therapy)

Cat (Feline)

Treatment of roundworms (Toxocara cati)
Treatment of hookworms (Ancylostoma tubaeforme)
Treatment of lungworms (Aelurostrongylus abstrusus)

Horse (Equine)

Treatment of large strongyles (Strongylus vulgaris, S. edentatus, S. equinus)
Treatment of small strongyles (Cyathostomins)
Treatment of roundworms (Parascaris equorum)
Treatment of pinworms (Oxyuris equi)

Cattle (Bovine)

Treatment of gastrointestinal nematodes (Ostertagia, Haemonchus, Trichostrongylus, Cooperia, Nematodirus)
Treatment of lungworms (Dictyocaulus viviparus)

Small Ruminants (Sheep / Goat)

Treatment of gastrointestinal nematodes (Haemonchus, Teladorsagia, Trichostrongylus, Cooperia, Nematodirus)
Treatment of lungworms (Dictyocaulus filaria)

Rabbit & Small Mammals

Treatment of gastrointestinal nematodes (Passalurus ambiguus)
Treatment of lungworms (Protostrongylus spp.)

Avian & Poultry

Treatment of roundworms (Ascaridia galli)
Treatment of cecal worms (Heterakis gallinarum)
Treatment of gapeworms (Syngamus trachea)

Exotic & Other Species

Treatment of nematodes in reptiles (e.g., oxyurids, ascarids)
Treatment of nematodes in small mammals (e.g., guinea pigs, hamsters)

Pharmacology & Mechanism of Action

Drug Class: Anthelmintic | Pharmacological Group: Imidazothiazole

Mechanism of Action: Levamisole acts as a nicotinic acetylcholine receptor agonist at the neuromuscular junction of nematodes. It causes depolarizing neuromuscular blockade, leading to spastic paralysis of the parasite, which is then expelled by peristalsis. It also inhibits fumarate reductase, interfering with the parasite's energy metabolism. In addition, levamisole has immunomodulatory effects in mammals, stimulating T-cell function and phagocytosis.

Pharmacodynamics: Levamisole is rapidly acting against susceptible nematodes, causing paralysis and death within hours. It is effective against both adult and larval stages of many gastrointestinal and lung nematodes. Its immunostimulant properties are dose-dependent and are used in some adjunctive therapies, though the clinical significance in veterinary medicine is debated.

⚡ Pharmacokinetics Summary

Absorption: Levamisole is rapidly and almost completely absorbed after oral administration in most species. Peak plasma concentrations occur within 1-2 hours. It is also absorbed through the skin and mucous membranes.

Distribution: Levamisole is widely distributed throughout the body, with high concentrations in the liver, kidneys, and lungs. It crosses the blood-brain barrier to a limited extent. It is distributed into milk and crosses the placenta.

Metabolism: Levamisole is extensively metabolized in the liver, primarily by oxidative pathways. Metabolites include p-hydroxy-levamisole and other oxidation products.

Excretion: Levamisole and its metabolites are excreted primarily in the urine (about 70%) and feces (about 30%). In ruminants, a significant portion may be excreted in milk.

Half-Life: Dog: 1.8-4 hours; Cat: 2-3 hours; Horse: 2-4 hours; Cattle: 4-6 hours; Sheep: 2-3 hours.

Bioavailability: Oral bioavailability is high, ranging from 70-100% in most species, though it may be reduced in ruminants due to ruminal degradation.

Protein Binding: Approximately 20-30% bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 50 mg, 100 mg, 200 mg (PO)

Oral Solution/Drench 18.15 mg/mL (for cattle, sheep) (PO)

Injectable Solution 136.5 mg/mL (for cattle, sheep) (SC)

Feed Additive/Premix Various concentrations (e.g., 0.08% in feed) (PO)

Topical Pour-On 10% solution (for cattle) (Topical)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to levamisole
Concurrent use with organophosphate anthelmintics or cholinesterase inhibitors
Severe hepatic or renal impairment
Debilitated or severely parasitized animals (risk of endotoxic shock from dying parasites)
Use in animals with a history of seizures
Do not use in cats with heartworm disease (risk of pulmonary thromboembolism)

Warnings & Clinical Precautions:

Use with caution in animals with compromised liver or kidney function.
In cattle, avoid intravenous administration; use subcutaneous route only.
In horses, do not administer to pregnant mares unless benefits outweigh risks.
In dogs, use with caution in breeds sensitive to neurotoxicity (e.g., Collies) due to potential MDR1 mutation.
Do not use in animals with severe debilitation or malnutrition.
Monitor for signs of toxicity, especially in cats and small animals.
Wash hands after handling; avoid skin contact.
In food animals, observe withdrawal times.
Do not use in animals intended for breeding unless advised by a veterinarian.

Adverse Effects & Reactions

Common:

Vomiting
Diarrhea
Salivation
Anorexia
Lethargy
Muscle tremors

Serious / Severe:

Seizures
Ataxia
Respiratory distress
Pulmonary edema
Hepatotoxicity
Agranulocytosis (rare)
Anaphylaxis

Rare:

Hemolytic anemia
Thrombocytopenia
Skin reactions
Neurotoxicity

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Organophosphate anthelmintics (e.g., dichlorvos, trichlorfon)	Additive cholinesterase inhibition leading to increased risk of toxicity (muscle tremors, salivation, respiratory failure).	High
Pyrantel	Similar mechanism of action; concurrent use may increase toxicity.	Moderate
Piperazine	Antagonistic effect on neuromuscular blockade; may reduce efficacy of levamisole.	Moderate
Neuromuscular blocking agents (e.g., succinylcholine)	Additive neuromuscular blockade; increased risk of respiratory paralysis.	High
Corticosteroids	May reduce immunostimulatory effects of levamisole.	Mild
Warfarin	Levamisole may enhance anticoagulant effect; monitor for bleeding.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Excessive salivation
Vomiting
Muscle tremors
Ataxia
Seizures
Respiratory depression
Collapse
Coma

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent oral ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Control seizures with diazepam or barbiturates. Provide respiratory support (oxygen, ventilation) as needed. Atropine may be used to counteract cholinergic effects (e.g., bradycardia, salivation) but is not a specific antidote. Monitor vital signs and provide fluid therapy for shock.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 3 days

Withdrawal times vary by country and formulation. For cattle and sheep: meat 7 days, milk 3 days. For poultry: meat 5 days, eggs 0 days (if approved). Always follow label and local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light. Keep container tightly closed. Avoid freezing. Store in a dry place.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in cattle, sheep, and swine in the US. Not approved for use in horses, dogs, cats, or poultry, but may be used extra-label.

Extra-Label (Off-Label) Use: In the US, levamisole is approved for use in cattle, sheep, and swine. Extra-label use in other species is permitted under AMDUCA with a valid veterinarian-client-patient relationship. For food animals, extended withdrawal times may be required.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Levamisole is a broad-spectrum anthelmintic effective against many gastrointestinal and lung nematodes. It is generally well-tolerated in ruminants but has a narrow margin of safety in cats and some dogs. Due to its immunomodulatory properties, it has been used as an adjunctive therapy in some cancers and immune-mediated diseases, but evidence is limited. In food animals, strict withdrawal times must be observed. Resistance has been reported in some nematode populations, so rotational deworming strategies are recommended. Always confirm diagnosis and use appropriate dosing based on species and weight.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)