Thiabendazole

Anthelmintic Benzimidazole

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 50 mg/kg q24h Duration: 2-3 days
Notes: For roundworms and hookworms. For lungworms, 50 mg/kg q24h for 5 days.
Cat PO 50 mg/kg q24h Duration: 2-3 days
Notes: For roundworms and hookworms. For lungworms, 50 mg/kg q24h for 5 days.
Horse PO 44 mg/kg Once Duration: Single dose
Notes: For strongyles and ascarids. May repeat in 2 weeks for severe infections.
Cattle PO 66-110 mg/kg Once Duration: Single dose
Notes: For gastrointestinal nematodes. Higher dose for lungworms.
Sheep/Goat PO 44-66 mg/kg Once Duration: Single dose
Notes: For gastrointestinal nematodes.
Rabbit PO 50 mg/kg q24h Duration: 3 days
Notes: For pinworms.
Poultry PO 100-200 mg/kg Once Duration: Single dose
Notes: For ascarids and capillaria.

Clinical Indications & Species Uses

General Indications
  • Treatment of internal parasites in various species
Dog (Canine)
  • Gastrointestinal nematodes (roundworms, hookworms, whipworms)
  • Lungworms (Capillaria aerophila)
  • Cutaneous larva migrans (as adjunctive therapy)
Cat (Feline)
  • Gastrointestinal nematodes (roundworms, hookworms)
  • Lungworms (Aelurostrongylus abstrusus)
Horse (Equine)
  • Gastrointestinal nematodes (strongyles, ascarids, pinworms)
  • Lungworms (Dictyocaulus arnfieldi)
Cattle (Bovine)
  • Gastrointestinal nematodes (Ostertagia, Cooperia, Haemonchus, Trichostrongylus)
  • Lungworms (Dictyocaulus viviparus)
Small Ruminants (Sheep / Goat)
  • Gastrointestinal nematodes (Haemonchus, Teladorsagia, Trichostrongylus)
  • Lungworms (Dictyocaulus filaria)
Rabbit & Small Mammals
  • Gastrointestinal nematodes (Passalurus ambiguus)
Avian & Poultry
  • Gastrointestinal nematodes (Ascaridia, Capillaria)
Exotic & Other Species
  • Gastrointestinal nematodes in reptiles and small mammals

Pharmacology & Mechanism of Action

Drug Class: Anthelmintic | Pharmacological Group: Benzimidazole

Mechanism of Action: Thiabendazole exerts its anthelmintic effect by binding to tubulin, inhibiting microtubule polymerization. This disrupts cellular functions in the parasite, including glucose uptake and intracellular transport, leading to depletion of glycogen stores and eventual death of the parasite. It is effective against a broad spectrum of nematodes and some other parasites.

Pharmacodynamics: Thiabendazole is a broad-spectrum anthelmintic with activity against gastrointestinal and lung nematodes, as well as some cestodes and trematodes. It is particularly effective against strongyles, ascarids, hookworms, and whipworms. The drug is also active against some ectoparasites and has anti-inflammatory properties, which are utilized in certain dermatological conditions.

⚑ Pharmacokinetics Summary

Absorption: Thiabendazole is rapidly and well absorbed from the gastrointestinal tract after oral administration. Peak plasma concentrations are typically reached within 1-2 hours in most species.
Distribution: The drug is widely distributed throughout the body, including into tissues and body fluids. It crosses the blood-brain barrier and is distributed into milk. It is also present in the liver and kidneys.
Metabolism: Thiabendazole is extensively metabolized in the liver, primarily to 5-hydroxythiabendazole, which is also pharmacologically active. Metabolism may involve cytochrome P450 enzymes.
Excretion: Excretion occurs primarily via the kidneys, with metabolites and some unchanged drug eliminated in urine. A significant portion is also excreted in feces. In ruminants, a large fraction is excreted in the bile and undergoes enterohepatic circulation.
Half-Life: The elimination half-life is approximately 1-2 hours in dogs and cats, 2-4 hours in horses, and 4-6 hours in cattle.
Bioavailability: Oral bioavailability is high, estimated at 80-90% in most species, due to rapid and complete absorption.
Protein Binding: Thiabendazole is approximately 90% bound to plasma proteins.

Available Formulations & Strengths

Oral Powder 50% powder (PO)
Oral Paste 43% paste (PO)
Oral Suspension 10% suspension (PO)
Oral Bolus 2 g, 4 g boluses (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to thiabendazole or other benzimidazoles
  • Hepatic or renal disease (use with caution)
  • Pregnancy (especially first trimester) unless benefit outweighs risk
  • Do not use in animals with known bone marrow suppression
Warnings & Clinical Precautions:
  • Use with caution in debilitated or severely parasitized animals, as rapid kill of parasites may cause toxemia.
  • In cattle, do not administer within 3 days of slaughter; milk withdrawal is 96 hours.
  • In horses, do not use in mares during the last month of pregnancy unless directed by a veterinarian.
  • May cause inappetence and transient weight loss in some animals.
  • Avoid use in animals with liver dysfunction.
  • Wear gloves when handling the drug to avoid skin absorption.

Adverse Effects & Reactions

Common:

  • Vomiting
  • Diarrhea
  • Anorexia
  • Lethargy
  • Salivation

Serious / Severe:

  • Hepatotoxicity
  • Bone marrow suppression
  • Teratogenic effects
  • Neurological signs (ataxia, seizures)

Rare:

  • Allergic reactions
  • Hemolytic anemia
  • Stevens-Johnson syndrome

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Other benzimidazoles (e.g., fenbendazole, oxfendazole) Additive anthelmintic effects and potential for increased toxicity. Moderate
Cimetidine May increase plasma levels of thiabendazole by inhibiting its metabolism. Moderate
Phenytoin May decrease thiabendazole levels due to enzyme induction. Mild
Theophylline Thiabendazole may increase theophylline levels, leading to toxicity. High

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea
  • Ataxia
  • Tremors
  • Seizures
  • Respiratory depression
  • Hepatic necrosis

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide IV fluids, anticonvulsants (e.g., diazepam) for seizures, and monitor liver function. In severe cases, consider hemodialysis.

Food Animal Withdrawal Times

πŸ₯© Meat: 3 daysπŸ₯› Milk: 4 days

Withdrawal times are for cattle and sheep. For other species, consult local regulations. Not approved for use in poultry in some countries; check label.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (15-30Β°C)

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in cattle, sheep, goats, horses, dogs, and cats. Not approved for use in poultry in the US.

Extra-Label (Off-Label) Use: Extra-label use in food animals requires a valid veterinary-client-patient relationship and must comply with AMDUCA regulations. Withdrawal times may need to be extended.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Thiabendazole is an older benzimidazole anthelmintic with a relatively narrow spectrum compared to newer agents. It is still used in some species for specific parasites, but resistance is common in some nematode populations. It has anti-inflammatory properties and has been used topically for dermatophytosis in some species, though this is not a labeled indication. Due to its potential for toxicity and the availability of safer alternatives, it is not a first-line choice in many cases. Always confirm the diagnosis and susceptibility before use. In food animals, adhere strictly to withdrawal times.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)