Pyrantel is an anthelmintic, which acts as an agonist of nicotinic receptors (AChRs) of nematodes and exerts its therapeutic effects by depolarizing their muscle membranes. It is used to treat a number of parasitic worm infections. This includes ascariasis, hookworm infections, enterobiasis (pinworm infection), trichostrongyliasis and trichinellosis. Common adverse reactions include diarrhea, nausea, vomiting, dizziness, headache and somnolence.

Praziquantel, (-)- is oxopyrazinoisoquinoline derivative and a levorotated isomer of Praziquantel patented by Merck Patent G.m.b.H. as anthelmintics agent. In rabbits infested with S. japonicum, the therapeutic effect of Praziquantel, (-)-was greater than that of dl-praziquantel as rated by the number of the worms in tissues and by liver damage. Histopathological examination showed that liver egg granulomas in the levo-praziquantel group were fewer in no. and smaller in size and were predominantly composed of Pseudotubercles instead of eosinophilic abscesses. Levo-praziquantel is therapeutically superior to praziquantel, while dextro-praziquantel is almost ineffective.

Praziquantel, (+)- is the dextrorotated (+) isomer of Praziquantel. Praziquantel (PZQ) is the drug of choice against schistosomiasis. Since exposure of schistosomes to the drug is associated with calcium influx and muscular contraction, calcium channels have been suggested as the target. It is a specific pharmacological effect seen exclusively with the active levo-R(-)stereo isomer of the drug. Praziquantel, (+)- apparently contributes little to the therapeutic efficacy of Praziquantel. In vivo, single 400-mg/kg oral doses of Praziquantel, (-)- and Praziquantel, (+)- achieved worm burden reductions of 100 and 19%, respectively. Moreover, worms treated in vivo with Praziquantel, (+)- displayed an only transient hepatic shift and returned to the mesenteric veins within 24 h.

Emodepside is a semi-synthetic product (originated by Astellas and out-licensed to Bayer for animal and human use); its precursor is synthesized by a fungus living in the leaves of Camellia japonica. It is a potent antihelminthic drug used in combination with praziquantel (as Profender®) and in combination with toltrazuril (as Procox®) for the treatment of parasitic worms in cats and dogs. Emodepside, a semi-synthetic derivative of PF1022A, belongs to a new class of anthelmintic drugs, the cyclooctadepsipeptides, and shows good efficacy against macrocyclic lactone-, levamisole- or benzimidazole-resistant nematode populations. Although putative receptors for emodepside have already been discovered, its mode of action is still not fully understood. It has being suggested that GABA(A)-receptor UNC-49 is associated with the emodepside mode of action. It has also being shown that Emodepside binds to a presynaptic latrophilin receptor in nematodes. The following presynaptic signal transduction occurs via activation of Gqalpha protein and phospholipase-Cbeta, which leads to mobilization of diacylglycerol (DAG). DAG then activates UNC-13 and synaptobrevin, two proteins which play an important role in presynaptic vesicle-functioning. This finally leads to the release of a currently unidentified transmitter. The transmitter (or modulator) exerts its effects at the postsynaptic membrane and induces a flaccid paralysis of the pharynx and the somatic musculature in nematodes.

Fenbendazole (FBZ) is a broad-spectrum benzimidazole antiparasitic drug currently approved for use in numerous animal species, including rodents. Although nematodes, and in particular pinworms, are the main endoparasites of concern in laboratory rodents, FBZ also is indicated for use in other animal species against a wide spectrum of nematodes, tapeworms, flukes, and protozoa (Giardia duodenalis, Encephalitozoon intestinalis). The molecular mode of fenbendazole action consists in
binding of beta-tubulin monomer prior to dimerisation with alfa-tubulin which blocks subsequent microtubule formation. These microtubules are important organelles involved in the motility, the division and the secretion processes of cells in all living organisms. In the worms the blocking of microtubules perturbs the uptake of glucose, which eventually empties the glycogen reserves. This blocks the whole energy management mechanism of the worms that are paralyzed and die or are expelled. FBZ have a greater binding to nematode as compared to mammalian tubulin at 37°C. The oral LD50 of p-OH fenbendazole was >10 000 mg/kg b.w. in mice and rats.

Moxidectin is a semi-synthetic methoxime derivative of LL F-2924α, commonly referred as F-alpha or nemadectin F-alpha is a product of fermentation of Streptomyces cyaneogriseus subsp. noncyanogenus, a bacterial organism isolated in 1983 from a sample of sand from Victoria, Australia. Moxidectin is a potent, broad-spectrum endectocide with activity against a wide range of nematodes, insects and acari. The compound acts by binding to ligand-gated chloride channels, more specifically the subtypes that are gamma-aminobutyric (GABA) mediated and glutamate-gated. The consequence of Moxidectin binding and activation is an increased permeability, leading to an influx of chloride ions and flaccid paralysis of the parasite leading to death. The macrocyclic lactones probably act by binding to and opening glutamate-gated chloride channels found only in neurons and myocytes of invertebrates. Because moxidectin is very lipophilic, it becomes highly concentrated in the serum. When the concentration of moxidectin in the serum is high, moxidectin is able to cross the blood-brain barrier. Once it is in the central nervous system, a macrocyclic lactone stimulates the synaptic secretion of the inhibitory neurotransmitter, GABA. By binding at the receptor site, GABA causes influx of chloride ions into neurons, causing the neurons to become hyperpolarised, which in turn, causes diminution in neuronal activity, resulting in sedation and relaxation of the skeletal muscles. Signs displayed by foals with moxidectin toxicity included dyspnoea, depression, ataxia, weakness, coma and seizures. In a Phase 3 study compared the efficacy, safety and tolerability of moxidectin and ivermectin in subjects infected with Onchocerca volvulus, which is the parasite that causes river blindness.