Pastes and gels are ready-to-use formulations for oral administration that are broadly used as delivery forms of horse anthelmintics, together with feed additives. Whereas feed-additives are also broadly used for livestock, pastes and gels are not used on livestock at all.
Pastes and gels belong to the so-called semi-solid formulations (i.e. neither solid nor liquid, but inbetween). They are vastly used for ointments, creams and the like that are applied topically, i.e. to the skin of animals and also humans.
Most commercial RTU pastes and gels are sold in pre-charged syringes or tubes that are rather easy to handle and allow single or multiple, depending on horse weight and dose. These products are basically designed for treating one or a few animals, not herds as is always the case for livestock antiparasitics. On this regard, horse products resemble more pet than livestock products. And as pet products, they are also significantly more expensive than livestock products with comparable active ingredients and indications. Equine feed additives are usually the cheaper alternative to pastes and gels, but not all active ingredients are available as feed-additives too.
Pastes and gels are almost exclusively dewormers, i.e. use for controlling parasitic worms of horses, mainly roundworms and/or tapeworms. It is very unusual that flukes become a problem for horses, and for this reason, almost no equine dewormer contains an effective flukicide.
Many horse owners complain about the high prices of ivermectin formulations (mostly pastes or gels) for horses when compared with injectables for cattle and other livestock. Apparently, the reason why ivermectin livestock injectables are normally not used on horses is that shortly after introduction, it was noticed that horses were more prone to develop severe clostridial infections at the injection site (due to contamination of the needles) and other undesired side effects than cattle or sheep. In addition, the pharmacokinetic behavior of ivermectin on horses is different than in ruminants. For these reasons oral pastes (or gels) were developed for horses that do not show such side effects.
Active ingredients of oral pastes & gels
- Benzimidazoles: (e.g. fenbendazole, mebendazole, oxfendazole), broad-spectrum wormers mainly against roundworms
- Isoquinolines: mainly praziquantel, only against tapeworms
- Macrocyclic lactones: mainly abamectin, ivermectin & moxidectin: broad-spectrum wormers only against roundworms and stomach bots (Gasterophilus intestinalis)
- Tetrahydropyrimidines: (mainly pyrantel tartrate or pamoate, also morantel) only against some gastrointestinal roundworms and some tapeworm species.
Macrocyclic lactones used on horses (ivermectin & moxidectin) are usually not approved for the control of any external parasites such as mites & lice that can affect horses, against which they are theoretically effective as well. This is in contrast with many macrocyclic lactone formulations used on livestock (injectables, pour-ons). The reason is that for controlling such external parasites a higher dose would be required.
Correct administration is a must to ensure efficacy. It includes accurate determination of the animal's weight, and ensuring that the horse does actually swallow the delivered amount. To ensure this, the horse's mouth should be empty when dosing. Apply the syringe into the corner of the mouth at about 45 degrees to his head, (there are no teeth there). Slowly push the syringe into the mouth, press the plunger while gently wiggling the syringe to deposit the paste across the tongue, i.e. avoid depositing a large lump of paste at one place: this would make it easier for the horse to spit it out. Then lift the head of the horse until it has swallowed the paste. In any case follow the product use instructions.
For an overview and a list of the most used oral paste & gel brands click here.
Safety of orals pastes & gels
Oral pastes & gels wormers are usually save for horses. The active ingredients used are well tolerated and the safety margins of the products used are usually rather high, i.e., the risk of unexpected adverse reactions in case of slight overdosing is quite low.
However, each active ingredient has it own safety profile. For additional information in this site, read the safety profiles of particular active ingredients most used in equine pastes and gels:
- Abamectin safety
- Fenbendazole safety
- Ivermectin safety
- Mebendazole safety
- Morantel safety
- Moxidectin safety
- Oxfendazole safety
- Praziquantel safety
- Pyrantel safety
Parasite resistance to oral pastes & gels
Resistance of small strongyles (cyathostomins) is widespread and can be rather high, particularly to benzimidazoles (e.g. fenbendazole, oxibendazole, mebendazole, etc). In a recent survey resistance to benzimidazoles was confirmed in >80% of the investigated yards in UK and Germany. It is known to be also frequent in the US, Australia and in many other countries. Resistance to tetrahydropyrimidines (e.g. morantel, pyrantel) has also been reported in Europe and the USA, but not as high and frequent as to benzimidazoles, and often a useful degree of efficacy can be still achieved. Tolerance to macrocyclic lactones (e.g. ivermectin, moxidectin), manifested as a low but significant worm egg output after treatment (determined after fecal egg counts) is not yet widespread, but has been already reported in Europe (e.g. in the UK, Germany, Italy), the USA, and Brazil.
Resistance of Parascaris equorum to most commonly used anthelmintics is increasing. Resistance to macrocyclic lactones (e.g. ivermectin, moxidectin) has been reported in the USA, UK and Australia. Tolerance (i.e. reduced efficacy) to benzimidazoles (e.g. fenbendazole, oxibendazole, etc) has also been reported in the USA, and resistance to pyrantel is also known to occur in several countries (e.g. Australia, USA, Brazil, Japan). There are also reports on cases of multi-resistance to macrocyclic lactones and tetrahydropyrimidines, e.g. in the USA.