Closantel is an antiparasitic active ingredient used in veterinary medicine against internal parasites (e.g. blood-sucking roundworm species, liver flukes) and some external parasites (e.g. sheep nasal bots, cattle grubs, sheep keds, etc.) of livestock. It is ineffective against lungworms or other roundworms outside the gastrointestinal tract. It belongs to the chemical class of the salicylanilides.
Closantel is used mainly in ruminants, often in combination with other nematicides (e.g. benzimidazoles, macrocyclic lactones, levamisole) mainly in drenches and injectables for cattle, sheep, goats and Southamerican camelids. It is also available as pastes or gels for horses (mainly in Latin America) and as a pour-on for cattle. So far it is not used in pigs, poultry, or companion animals. It is not used either against agricultural or household pests.
Although it is a rather old active ingredient introduced in the 1970's, usage of closantel in ruminants has increased in the last years in order to encounter increasing resistanceof gastrointestinal roundworms to other nematicides such as benzimidazoles, macrocyclic lactones and levamisole.
In contrast with many other anthelmintics (e.g. imidazothiazoles, benzimidazoles, tetrahydropyrimidines), closantel does have a residual effect, i.e. it not only kills the parasites present in the host at the time of treatment, but protects against re-infestation for a period of time (up to several weeks) that depends on the dose and the specific parasite.
Resistance to closantel has been reported for Haemonchus roundworms and liver flukes (Fasciola hepatica) in sheep, but so far seems not to be widespread in most countries.
The table below indicates some usual dosing recommendations for closantel issued by manufacturers or documented in the scientific literature. They may not be approved in some countries.
| Dosing recommendations for CLOSANTEL |
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| CATTLE | ||
| Delivery | Parasites | Dose (against closantel-susceptible parasites) |
| Oral | Gastrointestinal roundworms | 5-10 mg/kg |
| Oral | Hypoderma spp | 10 mg/kg |
| Subcutaneous | Gastrointestinal roundworms | 3 mg/kg |
| Subcutaneous | Fasciola hepatica | 5 mg/kg |
| Topical | Gastrointestinal roundworms | 20 mg/kg |
| SHEEP | ||
| Delivery | Parasites | Dose (against closantel-susceptible parasites) |
| Oral | Gastrointestinal roundworms | 5-10 mg/kg |
| Oral | Oestrus ovis | 5 mg/kg |
| Oral | Fasciola hepatica | 10 mg/kg |
| Subcutaneous | Gastrointestinal roundworms | 5-10 mg/kg |
| GOATS | ||
| Delivery | Parasites | Dose (against closantel-susceptible parasites) |
| Oral | Gastrointestinal roundworms | 10 mg/kg |
| Subcutaneous | Gastrointestinal roundworms | 5 mg/kg |
| HORSES | ||
| Delivery | Parasites | Dose (against closantel-susceptible parasites) |
| Oral | Gastrointestinal roundworms | 10 mg/kg |
| Oral | Fasciola hepatica | 10 mg/kg |
| Oral | Anaplocephala spp | 10 mg/kg |
| SOUTHAMERICAN CAMELIDS |
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| Delivery | Parasites | Dose (against closantel-susceptible parasites) |
| Oral | Gastrointestinal roundworms | 5 mg/kg |
| Subcutaneous | Gastrointestinal roundworms | 4-8 mg/kg, rep 10-14 days later |
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In most finished products, efficacy and safety depend not only on the amount of active ingredient(s) but also on their formulations (i.e. the type and amount of so-called inert ingredients), particularly in injectables and in topical pour-ons and spot-ons. These inert ingredients can significantly affect the pharmacokinetic behavior (e.g. absorption through the skin or from the injection site, distribution within the body, spreading throughout the body surface, etc). Generic products usually contain the same amount of active ingredient(s) as the original product, but often in quite different formulations. In many cases, the curative (therapeutic) efficacy of the different formulations is quite comparable, but the protective (prophylactic) efficacy that determines the length of protection against re-infestations may be rather different.
Dosing recommendations for antiparasitics depend on national regulations. National regulatory authorities determine whether a product is approved for a given indication, i.e. use on a particular host at a specific dose and against a specific parasite. Check the labels of the products available in your country for specific information on approved indications.
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