Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Available forms7 forms · 13 strengths documentedShow all ↓
Tablet 50 mgBolus 0.184 g livestockBolus 2.19 g livestock
Oral solution 25 mg/mL compounded
Soluble drench powder 46.8 g packet livestockSoluble drench powder 362.7 g bottle livestockSoluble drench powder 544.5 g bottle livestockSoluble powder 18.15 g bottle livestockPacket 9 gPacket 11.7 gPacket 18.15 g
136.5 mg/mL levamisole phosphate182 mg/mL levamisole phosphate
Overview
Levamisole is a broad-spectrum anthelmintic with antinematodal and immune-stimulating activity. Its use in veterinary medicine is currently limited because many oral products are no longer commercially marketed, mainly because of increasing parasite resistance and the potential for adverse effects.
In dogs, levamisole was historically used as a microfilaricide for the treatment of Dirofilaria immitis infection but is rarely used for this purpose today. It has also been used as an immunostimulant in the adjunctive treatment of certain neoplasms and in combination with glucocorticoids for systemic lupus erythematosus.
Mechanism of Action (MOA): Levamisole produces nicotine-like stimulation of the parasympathetic and sympathetic ganglia of susceptible nematodes. At higher concentrations, it interferes with carbohydrate metabolism by blocking fumarate reduction and succinate oxidation, causing paralysis and subsequent expulsion of the living worm. Its immune-stimulating mechanism is not fully understood but may involve restoration of cell-mediated immune function in peripheral T lymphocytes and stimulation of monocyte phagocytosis, particularly in immunocompromised animals.
Levamisole is absorbed from the gastrointestinal tract after oral administration, although its bioavailability is variable. It is distributed throughout the body and primarily metabolized, with less than 6% excreted unchanged in urine. Metabolites are eliminated mainly in urine and also in feces. The plasma elimination half-life in dogs is approximately 1.8–4 hours.
Indications
In dogs, levamisole has been used for the following indications:
- Heartworm infection: Historically used as a microfilaricide for Dirofilaria immitis infection, although it is rarely used for this purpose today.
- Neoplasia: Adjunctive immunostimulant therapy for various neoplasms.
- Systemic lupus erythematosus: Adjunctive treatment in combination with glucocorticoids.
- Endoparasites: Treatment of nematode infections, including the lungworm Crenosoma vulpis.
Dosage (Reference)
Dog
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Systemic lupus erythematosus (adjunctive therapy; extra-label) | PO | Levamisole: 2–5 mg/kg Maximum: 150 mg/dog Prednisone: 0.5–1 mg/kg every 12 hours |
Every 48 hours (levamisole) | Administer levamisole in combination with prednisone. Gradually taper the prednisone dose over 1–2 months.
Continue levamisole for 4 months or longer if relapse occurs. |
| Endoparasites | PO | 5–8 mg/kg | Once | Up to 10 mg/kg for 2 days. |
| Crenosoma vulpis (lungworm) | SC | 7.5 mg/kg | Every 48 hours | Two doses; few studies confirm the efficacy of anthelmintics for respiratory parasites, and most data are anecdotal. |
| Heartworm microfilaricide | PO | 10 mg/kg | Every 24 hours | For 6–10 days; macrocyclic lactones are recommended instead. |
| Immunostimulant | PO | 0.5–2 mg/kg | Three times per week | Reports of efficacy are lacking. |
| Hookworms | PO | 10 mg/kg per day | – | For 2 days. |
Cat
Levamisole dosages for cats are listed below.
| Clinical use | Route | Dose | Frequency | Notes |
|---|---|---|---|---|
| Endoparasites | PO | 4.4 mg/kg | Once | |
| Lungworms | PO | 20–40 mg/kg | Every 48 hours | For five treatments. |
Warnings & Precautions
Levamisole requires accurate dosing and careful patient selection because excessive doses may cause serious toxicity.
- Debilitated animals: Use cautiously in severely debilitated dogs and cats.
- Hepatic impairment: Use cautiously in animals with significant hepatic impairment.
- Accurate dosing: Accurately determine body weight before calculating the dose. Underdosing may result in ineffective treatment and encourage parasite resistance, while excessive dosing may cause toxicity.
- Feline viral infections: Contraindicated in cats with FIV or FIP and likely ineffective in cats with FeLV.
- Pregnancy and nursing: Safety has not been established. Use only when the potential maternal benefits outweigh the possible risks to the offspring.
- Human exposure: Avoid skin contact with liquid preparations because levamisole can be absorbed through the skin.
- Medication errors: Do not confuse levamisole with leucovorin, levetiracetam, or levocarnitine.
- High microfilaria burden: Use cautiously in animals with high heartworm microfilaria burdens, because reactions are possible from the heavy kill of microfilariae; check for microfilariae before treatment.
Drug Interactions
The following interactions have been reported or are theoretical. Concomitant use is not necessarily contraindicated unless otherwise stated; assess the potential risks and provide additional monitoring when appropriate.
- Anticholinesterases (e.g., neostigmine and organophosphates): May enhance the toxic effects of levamisole; use together with caution.
- Aspirin: Levamisole may increase salicylate concentrations.
- Chloramphenicol: Fatalities have been reported with concurrent administration; avoid using these drugs together.
- Nicotinic drugs (e.g., diethylcarbamazine, morantel, and pyrantel): May enhance the toxic effects of levamisole; use together with caution, although combining levamisole with pyrantel or morantel is not recommended because of similar mechanisms of action and toxicity.
- Warfarin: Concurrent administration may increase the risk of bleeding.
Side Effects & Overdose
Side Effects
- Dogs: Vomiting, diarrhea, panting, shaking, agitation or other behavioral changes, lethargy, dyspnea, pulmonary edema, immune-mediated anemia, agranulocytosis, and immune-mediated skin reactions, including erythroedema, erythema multiforme, and toxic epidermal necrolysis; thrombocytopenia has also been reported.
- Cats: Hypersalivation, excitement, mydriasis, and vomiting.
Overdose
Levamisole toxicity may resemble organophosphate poisoning. Signs may include hypersalivation, hyperesthesia, irritability, clonic seizures, CNS depression, dyspnea, defecation, urination, collapse, and cardiac arrhythmias. Acute overdose may cause death from respiratory failure.
- Treatment: Provide supportive care; affected animals generally recover within hours after dosing, and atropine sulfate can alleviate the clinical signs, although in an experimental study in dogs it was not sufficient on its own.
- Respiratory failure: Initiate artificial ventilation with oxygen and continue until recovery.
- Oral ingestion: Gastrointestinal decontamination and/or activated charcoal with a cathartic may be indicated.
- Toxic doses in dogs: A single oral dose of 12 mg/kg was believed responsible for bradycardia, tachypnea, hypothermia, cerebrocortical depression and diarrhea in one dog, and in an experimental study, 25 mg/kg given orally daily for 3 days caused severe neurological signs, gastric hemorrhage, bloody vomiting and deaths.
Keynotes
- When levamisole is administered orally to dogs, giving it with food may help prevent vomiting.
- Monitor treatment efficacy using appropriate clinical assessment; fecal flotation or a fecal egg count reduction test may be used when treating parasitic infections.
- A compounded 25 mg/mL oral solution prepared from levamisole hydrochloride retains more than 97% potency for 90 days when stored at 4°C or 25°C and protected from light; the solution is made by triturating 2.5 g of levamisole hydrochloride powder with 100 mL of sterile water.
