PRAZIQUANTEL

Praziquantel (Biltricide) is an anthelmintic effective against flatworms. Praziquantel is not licensed for use in humans in the UK; it is, however, available as a veterinary anthelmintic, and is available for use in humans on a named-patient basis.

USES

Praziquantel is used to treat diseases in humans and other mammals that are caused by infection with several types of internal/ gastrointestinal parasites including the following: 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.
Fascioliasis ("liver rot") brought on by either Fasciola hepatica (the common liver fluke) or Fasciola gigantica

HISTORY

Praziquantel was developed in the laboratories for parasitological research of Bayer AG and Merck KGaA in Germany (Elberfeld and Darmstadt) in the mid 1970s. The World Health Organization includes it on its Model List of Essential Medicines.

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 inhibit CYP3A4 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.

MODE OF ACTION

Although 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.

SIDE EFFECTS

The majority of side effects develop due to the release of the contents of the parasites as they are killed and the consequent host immune reaction. The heavier the parasite burden, the heavier and more frequent the side effects normally are. Central nervous system: Frequently occurring side effects are dizziness, headache, and malaise. Drowsiness, somnolence, fatigue, and vertigo have also been seen. Almost all patients with cerebral cysticercosis experience CNS side effects related to the cell-death of the parasites (headache, worsening of pre-existing neurological problems, seizures, arachnoiditis, and meningism). These side effects may be life-threatening and can be reduced by coadministration of corticosteroids. It is strongly recommended that all patients with cerebral cysticercosis are hospitalized during treatment. GI Tract: Approximately 90% of all patients have abdominal pain or cramps with or without nausea and vomiting. Diarrhea may develop and may be severe with colic. Sweating, fever, and sometimes bloody stools may occur together with diarrhea. Liver: Asymptomatic and transient increases of liver enzymes (AST and ALT) are noted frequently (up to 27%). No case of symptomatic liver damage has ever been seen so far. Sensitivity reactions: Urticaria, rash, pruritus and eosinophilia in white blood cell counts Other locations/body as a whole: Lower back pain, myalgia, arthralgia, fever, sweating, various cardiac arrhythmias, and hypotension.

DRUG INTERACTIONS

ANTIBIOTICS

A study found that the antibiotic rifampicin decreases plasma concentrations of praziquantel.

ANTIEPILEPTICS

Carbamazepine and phenytoin are reported to reduce the bioavailability of praziquantel.

ANTIMALARIALS

Chloroquine reduces the bioavailability of praziquantel

ANTACIDS / HISAMINE H2- ANTAGONISTS

At least 2 studies indicate the drug cimetidine heightens praziquantel bioavailability.

DOSAGE

For schistosomiasis, the dose is 20 milligrams/kilogram by mouth every 4–6 hours for one day. For tapeworms, the dose is 5–25 mg/kg by mouth once. For liver fluke, the dose is 25 mg/kg by mouth every 4–6 hours for one day. These dosages are for patients over 4 years old, and are to be taken with food or a few minutes before a meal.

BRAND NAMES

Biltricide (Bayer) 600 mg Tablets (for human use)
Cesol (Merck) Tablets
Cestoved (Vedco) both tablets and injectable for veterinary use Cysticide (Merck) Tablets
Droncit (Bayer) for veterinary use
Drontal (combination with pyrantel pamoate) (Bayer) for veterinary use
D-Worm (Farnum) for veterinary use; note that D-Worm also makes roundworm medicine containing piperidine which is not effective against tapeworms.
Kaicide (Taiwan)
Milbemax (combination with milbemycin oxime) (Novartis) for veterinary use
Popantel (Jurox)
PraziPro (Hikari) for aquarium use
Profender (combination with emodepside) (Bayer) for veterinary use
Tape Worm Tabs (Trade Winds) for veterinary use
Zentozide (Berich (Thailand) Co)
Distoside (Chandra Bhagat Pharma Pvt Ltd) 600mg tablet (for human use)

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