THE MERCK VETERINARY MANUAL
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Tetrahydropyrimidines

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Pyrantel was first introduced as a broad-spectrum anthelmintic against GI nematodes of sheep and has also been used in cattle, horses, dogs, cats, and pigs. It is available as a citrate, tartrate, embonate, or pamoate salt.

Aqueous solutions are subject to isomerization on exposure to light, with a resultant loss in potency; therefore, suspensions should be kept out of direct sunlight. It is not recommended for use in severely debilitated animals because of its levamisole-type pharmacologic action.

Pyrantel is used PO as a suspension, paste, drench, or tablets. Both pyrantel and morantel are effective against adult gut worms and larval stages that dwell in the lumen or on the mucosal surface.

Pyrantel tartrate is effective as a broad-spectrum anthelmintic in ruminants; however, its activity is mainly limited to the adult GI nematodes.

Pyrantel is effective against adult ascarids, large and small strongyles, and pinworms. At double the recommended dose, it has limited activity against the ileocecal tapeworm Anoplocephala perfoliata.

Pyrantel tartrate is used in swine for the treatment of Ascaris and Oesophagostomum.

Pyrantel pamoate or embonate is effective against the common GI nematodes, except for whipworms. Oxantel, a phenol analog of pyrantel, is combined with pyrantel in some anthelmintic preparations for dogs (and people) to increase activity against whipworms.

Last full review/revision September 2014 by Jozef Vercruysse, DVM; Edwin Claerebout, DVM, PhD, DEVPC

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