Morantel (1,4,5,6-tetrahydro-1-methyl-2-[2-(3-methyl-2-thienyl)ethenyl pyrimidine) is a tetrahydro-pyrimidine anthelmintic, differing from the related analogue pyrantel by the presence of a methyl group on the thiophene ring. Morantel tartrate, manufactured by Pfizer, Inc., was approved in the United States for use in cattle in 1981, and entered the market in early 1982. Three formulations have been approved in the United States: RUMATEL® Medicated Premix-88; RUMATEL Cattle Wormer Bolus, and PARATECT FLEX™ Diffuser, a sustained release bolus. It is intended to treat roundworms and tapeworms. Morantel is administered in lactating and non lactating cattle as morantel tartrate as a slow-release bolus (11.8 g morantel base per animal) or as a single oral dose of 6 to 7.5 mg morantel base/kg bw and in pigs at a single dose equivalent to 7.5 mg base/kg bw. In sheep, the citrate salt is administered at a single dose equivalent to 5 to 6 mg morantel base/kg bw. Morantel acts as a potent agonist at the acetylcholine receptors on the muscle cells of nematodes. Activation of the acetylcholine receptors induces a prolonged, spastic paralysis of the worms and expulsion from the host. It also been reported to block neurotransmission in vertebrates, to possess nicotine-like properties and to mimic acetylcholine at receptors in autonomic ganglia, adrenal medullae and respiratory tissues. Morantel and its salts are not used in human medicines.