Praziquantel ( CAS: 55268-74-1)

Praziquantel (Biltricide) is an anthelmintic effective against flatworms. Praziquantel is not licensed for use

in humans in theUK; it is, however, available as a veterinary anthelmintic, and is available for use in humans

on a named-patient basis.

It is on the World Health Organization’s List of Essential Medicines, a list of the most important medications

needed in a basic health system.

Medical uses

Praziquantel is used to treat diseases in humans, mammals, and fish that are caused by infection with several

types of internal/gastrointestinal, and external parasites including the following:

•     Salmon poisoning disease

•     Hydatid disease caused by infection of various organs with larval stages of tapeworms of the genus Echinococcus

•     Cysticercosis caused by infection of the brain and/or muscles with the eggs and larvae of the pork tapeworm

Taenia solium (though it has been judged less effective than albendazole in treatment of neurocysticercosis)

•     Feline taeniasis caused in cats by gastrointestinal infection with adult tapeworms of the species Taenia

taeniaeformis; used either alone or in combination with pyrantel pamoate

•     Toxocariasis in cats and dogs whose gut is infected with the roundworms/nematodes Toxocara cati or

Toxocara canis respectively; use is often combined with pyrantel

•     Schistosomiasis caused by trematodes of the genus Schistosoma. As of 2005, praziquantel is the

primary treatment for human schistosomiasis, for which it is usually effective in a single dose.

•     Clonorchiasis brought on by the Chinese liver fluke Clonorchis sinensis

•     Paragonimiasis caused by infection with lung flukes, mostly of the species Paragonimus westermani.

•     Fasciolopsiasis caused by intestinal fluke Fasciolopsis buski.

•     Diplozoon paradoxum and other Trematoda infections of many fish species.  

Mechanism of action

The mode of action is not exactly known at present, there is experimental evidence that praziquantel increases

the permeability of the membranes of schistosome cells towards calcium ions. The drug thereby induces

contraction of the parasites, resulting in paralysis in the contracted state. The dying parasites are dislodged

from their site of action in the host organism and may enter systemic circulation or may be destroyed by host

immune reaction (phagocytosis). Additional mechanisms including focal disintegrations and disturbances of

oviposition (laying of eggs) are seen in other types of sensitive parasites.

Another hypothesis concerning the mechanism of action of praziquantel has been recently reported. The drug

seems to interfere with adenosine uptake in cultured worms. This effect may have therapeutical relevance

given that the schistosome, as the taenia and the echinococcus (other praziquantel sensitive parasites), is

unable to synthesize purines such as adenosine de novo.

Bayer’s Animal Health Division website states, “Praziquantel is active against cestodes (tapeworms). Praziquantel

is absorbed, metabolized in the liver and excreted in the bile. Upon entering the digestive tract from the bile,

cestocidal activity is exhibited. Following exposure to praziquantel, the tapeworm loses its ability to resist digestion

by the mammalian host. Because of this, whole tapeworms, including the scolices (plural of “scolex”), are very

rarely passed after administration of praziquantel. In many instances only disintegrated and partially digested pieces

of tapeworms will be seen in the stool. The majority of tapeworms are digested and are not found in the feces.”

Praziquantel is administered as a racemate, but only the (R)-enantiomer is biologically active; the enantiomers may

be separated using a resolution of an amine obtained from praziquantel.

Pharmacokinetics

Praziquantel is well absorbed (approximately 80%) from the gastrointestinal tract. However, due to extensive first-pass

metabolism, only a relatively small amount enters systemic circulation. Praziquantel has a serum half-life of 0.8 to 1.5

hours in adults with normal renal and liver function. Metabolites have a half-life of 4 to 5 hours. In patients with

significantly impaired liver function (Child Pugh classes B ll///d C), the serum half-life is increased to 3 to 8 hours.

Praziquantel and its metabolites are mainly excreted renally; within 24 hours after a single oral dose, 70 to 80% is

found in urine, but less than 0.1% as the unchanged drug. Praziquantel is metabolized through the cytochrome P450

pathway via CYP3A4. Agents that induce or inhibitCYP3A4 such as phenytoin, rifampin, and azole antifungals

will affect the metabolism of praziquantel.

Praziquantel has a particularly dramatic effect on patients with schistosomiasis. Studies of those treated have shown

that within six months of receiving a dose of praziquantel, up to 90% of the damage done to internal organs due to

schistosomiasis infection can be reversed.