06 May Chemical Structure of Salicylanilides and its Uses in Everyday Life
Salicylanilides are a group of chemicals having a molecular structure that are effective against some roundworms, tapeworms, and/or flukes. Each salicylanilide has a specific range of activity and only works against particular parasites. They are rarely used on horses or pets, and are primarily utilized on cattle and sheep.
Several pharmaceutical companies introduced anthelmintic salicylanilides in the 1960s and 1970s.
All salicylanilides are seasoned anthelmintics that long ago lost their ability to be patented. Generic versions of those still in use are readily available and produced by various chemical companies (typically in China, India, Israel, Brazil, etc.).
Salicylanilides are the most pertinent for any use:
Effective against certain roundworms and flukes, Closantel widespread use in livestock, particularly in sheep, goats, and cattle. Not suitable for horses or pets.
Effective against different types of tapeworms and against rumen flukes is niclosamide (Paramphistomum spp) rarely used in horses, animals, and pets.
Effective against specific flukes is oxyclozanide. Nowadays, livestock rarely uses. Not suitable for horses or pets.
Effective against some roundworms and flukes is rafoxanide. Rarely applied to livestock. Not suitable for horses or pets.
Brotianide (effective against specific flukes) and resorantel are two more seasoned salicylanilides that have been utilized in the past as livestock anthelmintics (effective against various tapeworms and against rumen flukes). Nowadays, both have been largely abandoned.
The case of Closantel is intriguing. It is one of the few true endectocides, meaning that at the standard therapeutic dose, it inhibits a variety of endoparasites and ectoparasites. But unlike macrocyclic lactones, which have a broad spectrum of activity, it has a restricted spectrum. A few external parasites include screwworms (Cochliomyia spp., Chrysomya spp.), sheep nasal bots (Oestrus ovis), and sheep keds. Closantel is extremely effective against adult and immature liver flukes (Fasciola hepatica), several gastrointestinal roundworms (e.g., Bunostomum spp., Haemonchus spp., Oe (Melophagus ovinus). The most widely used salicylanilide without a doubt.
Although niclosamide is effective against certain blood flukes (Schistosoma spp.), rumen flukes (Paramphistomum spp.), and various tapeworms (e.g. Taenia spp., Moniezia spp.), it is rarely used on livestock and pets. In some nations, it is authorized for use as a human medicine. To manage the snails that spread schistosomiasis, also known as bilharziosis or snail fever, a deadly human illness in many tropical areas, it was first introduced as a molluscicide, or snail killer. Niclosamide is sometimes utilized as its sodium or lithium counterparts, which are a little more efficient.
Fasciola hepatica adult liver fluke is susceptible to oxyclozanide, while late immature stages are only partially resistant. Effectiveness against Paramphistomum spp. rumen flukes is likewise constrained. Animals are hardly ever given it.A few roundworms, including Haemonchus species and Bunostomum species, as well as adults and late immature stages of the liver fluke (Fasciola hepatica), are very susceptible to the drug rafoxanide. There are still a few products for cattle that include rafoxanide.
However, brotianide is ineffective against rumen flukes. It only works against adults and late immature stages of the liver flukes Fasciola hepatica and Fasciola gigantica (Paramphistomum spp). It has been superseded with substances that are more effective.
When treating rumen flukes and some types of livestock tapeworms, such as Moniezia spp. and Avitellina spp (Paramphistomum spp). Additionally, it has been substituted with more effective substances.
Combinations with other anthelmintics are fairly frequent. To increase the flukicidal efficacy of nematicides (such as ivermectin, levamisole, fenbendazole, albendazole, etc.) and to overcome resistance to important gastrointestinal roundworms to those nematicides, Closantel is frequently combined with them.
Salicylanilide action mechanism
Salicylanilides’ molecular method of action is not entirely understood. They are all uncouplers of oxidative phosphorylation, which disrupts the process by which ATP, the cellular “fuel,” is produced in the mitochondria of the cell. The parasite’s motility is affected, along with possibly other processes.
Oxyclozanide is primarily found in the liver, kidneys, and stomach after oral ingestion. It is progressively broken down and eliminated through bile and feces.
Following administration, rafoxanide and closantel are promptly absorbed into the circulation. They have a strong blood protein binding affinity, which keeps them in the blood for weeks. This explains their exceptional effectiveness against migratory fluke larvae that come into contact with blood in the tissues prior to reaching the bile ducts. The half-life in the host is around 15 days, which helps to explain why liver fluke and Haemonchus spp. roundworms are resistant for up to 60 days after treatment.
Niclosamide is eliminated through the feces almost entirely as the unmodified parent component since it is poorly absorbed in the gut. This could account for why it isn’t hazardous to pets and cattle.
Salicylanilides are often very well tolerated by livestock and pets. For brotianide, the safety margins are as low is 3, as high as 6 for closantel and rafoxanide, and as high as 20 for niclosamide.
Humans are permitted to consume niclosamide, even during pregnancy.
Closantel and rafoxanide often have one-month meat withholding periods, and their use is typically prohibited in breastfeeding dairy cows whose milk is intended for human consumption.