Chemistry - The prototypic benzimidazole, thiabendazole occurs as an odorless or nearly odorless, tasteless, white to practically white powder. It has a melting range of 296°-303°C and a pKa of 4.7. Thiabendazole is practically insoluble in water and slightly soluble in alcohol.
Storage/Stability/Compatibility - Thiabendazole tablets, boluses and oral suspension should be stored in tight containers.
Uses/Indications - Thiabendazole has been used for the removal of the following parasites in dogs: ascarids (Toxocara canis, T. leonina), Strongyloides stercoralis, and Filaroides. It has also been used systemically as an anti-fungal agent in the treatment of nasal aspergillosis and penicillinosis. Topical and otic use of thiabendazole for the treatment of various fungi is also commonly employed.
Thiabendazole is indicated (labeled) for the removal of the following parasites in cattle: Haemonchus spp., Ostertagia spp., Trichostrongylus spp., Nematodirus spp., Cooperia spp. and Oesophagostomum radiatum.
Thiabendazole is indicated (labeled) for the removal of the following parasites in sheep and goats: Haemonchus spp., Ostertagia spp., Trichostrongylus spp., Nematodirus spp., Cooperia spp., Chabertia spp., Bunostomum spp. and Oesophagostomum spp.
Thiabendazole is indicated (labeled) for the removal of the following parasites in horses: Strongylus spp., craterstomum spp., Oesphagodontus spp., Posteriostomum spp., Cyathostomum spp., Cylicocylus spp., Cylicostephanus spp., Oxyuris spp., and Parasacaris spp..
Thiabendazole is indicated (labeled) for the removal or prevention of the following parasites in swine: large roundworms (Ascaris suum) (prevention), and in baby pigs infested with Strongyloides ransomi.
Although not approved, thiabendazole has been used in pet birds and llamas. See the Dosage section for more information.
In many geographic areas, significant thiabendazole resistance problems have developed and for many parasites other anthelmintics would be a better choice for treatment.
Pharmacokinetics - Thiabendazole is relatively well absorbed (for a benzimidazole) and is distributed throughout body tissues. Peak levels occur in approximately 2-7 hours after dosing. Absorbed drug is rapidly metabolized in the liver by hydroxylation, glucuronidation and sulfate formation. Within 48 hours of dosing, 90% of the drug is excreted in the urine (as metabolites) and 5% in the feces. Less than 1% of the drug is excreted in the urine unchanged. Five days after a dose, the drug is virtually eliminated from the body.
Contraindications/Precautions - Thiabendazole has not been demonstrated to be a teratogen and is considered to be generally safe to use during pregnancy. However, in high doses it has been implicated in causing toxemia in ewes.
Adverse Effects/Warnings - At recommended doses, thiabendazole is usually well tolerated by approved species. In dogs, vomiting, diarrhea, hair loss and lethargy are possible side effects, notably with high dose or long-term therapy. Dachshunds have been reported to be particularly sensitive to thiabendazole. Toxic epidermal necrolysis (TEN) has been reported in dogs receiving thiabendazole, but the incidence appears to be very rare.
Overdosage/Toxicity - Thiabendazole has a safety margin of at least 20 times the recommended dose in horses. Doses of 800 - 1000 mg/kg are necessary to cause anorexia and depression in sheep. The minimum lethal dose is 700 mg/kg in cattle and 1200 mg/kg in sheep.
It is unlikely that a modest overdose would cause significant problems. If a massive overdose occurs, treat supportively and symptomatically. See the Adverse effects section for more information.
Drug Interactions - Thiabendazole may compete with xanthines (e.g., theophylline, aminophylline) for metabolizing sites in the liver, thereby increasing xanthine blood levels.
For susceptible parasites:
a) 44 mg/kg PO. (Robinson 1987)
b) 44 mg/kg; 88 mg/kg for ascarids. (Roberson 1988b)
c) 50 - 100 mg/kg PO (Brander, Pugh, and Bywater 1982)
a) 20 mg/kg orally as a single dose for helminthiasis (Chandrasekharan, 2002), (Chandrasekharan et.al., 1995), (Chandrasekharan, 1992).
b) 32 mg/kg orally for strongylosis resulted in a 84.6 – 95.3 % reduction in eggs per gram (EPG) (Chandrasekharan et.al., 1982).
Chandrasekharan,K. 2002. Specific diseases of Asian elephants.
Journal of Indian Veterinary Association Kerala 7:(3):31-34
a) Chandrasekharan,K., 1992. Prevalence of infectious diseases in elephants in Kerala and their treatment. In: Silas,E.G., Nair,M.K., and Nirmalan,G. (Editors), The Asian Elephant: Ecology, Biology, Diseases, Conservation and Management (Proceedings of the National Symposium on the Asian Elephant held at the Kerala Agricultural University, Trichur, India, January 1989). Kerala Agricultural University, Trichur, India pp. 148-155
b) Chandrasekharan,K., Cheeran,J.V., Nair,K.N.M., Ramanujam,K.N., and Radhakrishnan,K. 1982. Comparative efficacy of 6 anti-helminthics against strongylosis in elephants. Kerala Journal of Veterinary Science 13:15-20 Summary: Anthelmintic efficacy of six drugs was compared under field conditions against strongylosis in elephants. Mebendazole at 3 and 4 mg/kg, Levamisole 3 mg/kg and Morantel tartrate 5 mg/kg were proved to be 100% effective. Mebendazole at 2 mg/kg and 2.5 mg/kg, Thiabendazole at 32 mg/kg. Bephenium hydroxynaphthoate at 25 mg/kg and Disophenol at 3 mg/kg were found to be effective only in 79.1 to 92.2 %, 88.1 to 100%, 84.6 to 95.3 %, 85.9 to 100% and 68.3 to 84 % cases respectively.
Client Information - Shake suspension well before using. Follow veterinarian’s or label directions carefully.
Dosage Forms/Preparations/FDA Approval Status/Withdrawal Times- Food residue tolerances: 0.1 ppm in uncooked meat of cattle, pheasants, swine, sheep and goats. 0.05 ppm in milk.
Thiabendazole Oral Suspension 4 g/fl. oz. (135 mg/ml)
Equizole® Suspension (MSD); (OTC) Approved for use in dairy and beef cattle, sheep, goats, and horses. Milk withdrawal = 96 hours. Slaughter withdrawal = 3 days (cattle); 30 days (sheep & goats)
Thiabendazole Oral Suspension 6 g/fl. oz. (203 mg/ml)
Omnizole®-Six Wormer Suspension (MSD); (OTC) Approved for use in dairy and beef cattle, sheep, goats, and horses. Milk withdrawal = 96 hours. Slaughter withdrawal = 3 days (cattle); 30 days (sheep & goats)
Thiabendazole Oral Suspension (Drench) 25 g/fl. oz. (845 mg/ml)
TBZ® Cattle Wormer (Drench) (MSD); (OTC) Approved for use in dairy and beef cattle. Milk withdrawal = 96 hours. Slaughter withdrawal = 3 days
Thiabendazole Oral Suspension 17.5 g/fl. oz. (592 mg/ml)
Thibenzole® Sheep and Goat Wormer (MSD); (OTC) Approved for use in sheep and goats. Milk withdrawal = 96 hours. Slaughter withdrawal = 30 days
Thiabendazole Oral Paste 50% (500 mg/g), 43% (430 mg/g), 20% (200 mg/g)
TBZ® Cattle Wormer Paste 50%, TBZ® Wormer Paste 43% (MSD); (OTC) Approved for use in dairy and beef cattle. Milk withdrawal=96 hours. Slaughter withdrawal = 3 days
Thiabendazole Oral Boluses (Tablets) 15 g (cattle), 2 g (calf, sheep, goat)
TBZ® Calf, Sheep, and Goat Wormer (MSD); (OTC) Approved for use in non-lactating dairy and beef cattle, goats, and sheep. Slaughter withdrawal = 3 days (calves); 30 days (goats, sheep)
Thiabendazole Medicated Premixes are available in: 22%, 44.1%, 66.1%, 88.2% concentrations. A thiabendazole medicated block (15 g/lb) is also available. An oral suspension of thiabendazole (2 g/oz) in combination with piperazine (2.5 g/oz) is available for use in horses. It is a prescription only medication (Rx) with the proprietary name: Equizole® A (MSD).
Thiabendazole Oral Chewable Scored Tablets 500 mg; Mintezol® (Merck); (Rx)
Thiabendazole Oral Suspension 100 500 mg/5 ml, 120 ml bottle; Mintezol® (Merck); (Rx)
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