Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Overview
Fenbendazole is a broad-spectrum benzimidazole anthelmintic used in dogs and cats for the treatment of a wide range of gastrointestinal and respiratory parasites. It is commonly administered orally and is available in multiple formulations including granules, suspensions, and pastes.
It is effective against several nematodes, some cestodes, and certain protozoal infections such as Giardia. Fenbendazole is widely used due to its safety profile and flexibility in dosing regimens, including use in young and pregnant animals.
Mechanism of Action (MOA): Fenbendazole inhibits the fumarate reductase system in parasites, disrupting the citric acid cycle and impairing energy metabolism. It also reduces glucose uptake by the parasite, leading to energy depletion and death.
Indications
Fenbendazole is used in dogs and cats for the treatment of a wide range of gastrointestinal and respiratory parasitic infections, including nematodes, some cestodes, and certain protozoal infections.
- Gastrointestinal nematodes: Effective against roundworms (ascarids), hookworms, and whipworms, including some larval stages.
- Tapeworms (Taenia spp.): Used for treatment of certain cestodes; efficacy against Dipylidium caninum is partial and may be inconsistent.
- Protozoal infections (Giardia): Commonly used for management of giardiasis in both dogs and cats.
- Respiratory parasites: Used in the treatment of lungworm infections such as Aelurostrongylus abstrusus in cats and Oslerus osleri in dogs.
- Cardiopulmonary parasites: Used in dogs for infections such as Angiostrongylus vasorum.
- Other parasitic infections: May be used for parasites such as Capillaria aerophila and certain gastric nematodes (e.g., Physaloptera spp.) depending on clinical context.
Dosage (Reference)
Dog
In dogs, fenbendazole is used for treatment of gastrointestinal and respiratory parasites with dosing depending on parasite type, age, and clinical condition.
| Indication | Route | Dose | Notes |
|---|---|---|---|
| Roundworms / Tapeworms (<6 months) | PO | 50 mg/kg q24h for 3 days | Young dogs protocol. |
| Roundworms / Tapeworms (>6 months) | PO | 100 mg/kg single dose | Repeat every 3 months. |
| Capillaria spp. | PO | 50 mg/kg q24h | May require extended treatment up to 10 days. |
| Angiostrongylus vasorum | PO | 50 mg/kg q24h ≥10 days | Minimum duration; may vary clinically. |
| Oslerus osleri | PO | 50 mg/kg q24h for 7 days | Repeat course may be needed. |
| Aelurostrongylus abstrusus | PO | 20 mg/kg q24h for 3 days | Used in specific lungworm infections. |
| Giardiasis | PO | 50 mg/kg q24h for 5 days | Common protocol for Giardia. |
| Pregnant bitches | PO | 25 mg/kg q24h (day 40 → 2 days postpartum) | Approx. 25 days total course. |
• Dose and duration depend on parasite species and severity of infection.
• Some infections require extended or repeated courses.
• Routine deworming may be repeated every 3 months in some cases.
Cat
In cats, fenbendazole is used for treatment of intestinal and respiratory parasites, with dosing protocols varying based on indication and age.
| Indication | Route | Dose | Notes |
|---|---|---|---|
| Roundworms / Tapeworms (<6 months) | PO | 20 mg/kg q24h for 5 days | Young cats protocol. |
| Roundworms / Tapeworms (>6 months) | PO | 100 mg/kg single dose | Standard adult dosing. |
| Aelurostrongylus abstrusus | PO | 20 mg/kg q24h for 5 days | For lungworm infections. |
| Giardiasis | PO | 20 mg/kg q24h for 5 days | Common Giardia protocol. |
• Dose varies depending on parasite type and age.
• Multi-day regimens are commonly required for effective treatment.
• Monitor clinical response and repeat treatment if necessary.
Warnings & Precautions
Fenbendazole is generally considered a safe anthelmintic in dogs and cats, but appropriate dosing and monitoring are important to ensure effective and safe use.
- Product variability: Multiple formulations and concentrations are available; ensure accurate dosing based on the specific product used.
- Off-label use: Many indications and dosing regimens are extra-label and should be used under veterinary guidance.
- Incomplete efficacy (certain parasites): Activity against some cestodes (e.g., Dipylidium caninum) may be limited; alternative or additional treatment may be required.
- Bone marrow effects (rare): Bone marrow hypoplasia has been reported in dogs, although this appears to be uncommon.
- Pregnancy safety: Considered safe for use in pregnant animals when used at recommended doses.
- Extended treatment courses: Some infections require prolonged or repeated dosing; ensure compliance to achieve effective parasite control.
- General handling: Standard precautions should be followed when handling the drug.
Drug Interactions
No clinically significant drug interactions have been reported for fenbendazole in dogs and cats based on available data.
- No known interactions: Fenbendazole is generally considered safe to use alongside other medications without documented interaction concerns.
Side Effects & Overdose
Side Effects
Fenbendazole is generally well tolerated in dogs and cats, and adverse effects are uncommon.
- Bone marrow hypoplasia: Rarely reported in dogs; clinical significance appears low but should be considered if unexplained hematologic changes occur.
Overdose
Specific information regarding acute overdose in dogs and cats is limited, and clinically significant toxicity appears uncommon.
- Limited data: No well-documented overdose syndromes reported in small animals.
- Management: Supportive care and monitoring are recommended if excessive dosing is suspected.
Key Notes
Practical clinical points to optimize the use of fenbendazole in dogs and cats:
- Broad-spectrum coverage: Effective against multiple parasite groups, making it a versatile choice in mixed infections.
- Larval stage activity: Has activity against certain larval stages of parasites, which can improve treatment outcomes.
- Giardia role: Commonly included in treatment protocols for giardiasis as an alternative or adjunct to other therapies.
- Flexible formulations: Available in multiple oral forms (granules, suspensions, paste), allowing easier administration across different patient types.
- Targeted treatment approach: Selection of dose and duration should be based on the specific parasite involved rather than using a single universal regimen.
- Monitoring efficacy: Clinical improvement and, when needed, follow-up fecal examinations help confirm treatment success.
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