Praziquantel

Praziquantel (Biltricide) is an anthelmintic effective against flatworms. As of 2005, praziquantel is the primary treatment for human schistosomiasis, for which it is usually effective in a single dose. It is also used to treat echinococcosis, cysticercosis, intestinal tapeworms and the liver flukes except for fascioliasis. In veterinary medicine it is widely used against tapeworms, going by the trade name of Droncit®.

Praziquantel is not licensed for use in humans in the UK; it is however available as a veterinary antibiotic, and is available for use in humans on a named-patient basis.

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History

Praziquantel was developed in the laboratories for parasitological research of Bayer AG in Germany (Elberfeld) in the mid 1970s. Since then it has proven indispensable in more and more indications and is recognized as such by the World Health Organization.

Pharmacokinetics

Praziquantel is well (approximately 80%) absorbed from the gastrointestinal tract. Due to extensive first-pass metabolization only relatively small amounts enter systemic circulation. Praziquantel has a serum halflife of 0.8 to 1.5 hours (metabolites 4 to 5 hours) in adults with normal renal and liver function. In patients with significantly impaired liver function (Child Pugh classes B and C) the serum halflife is increased to 3 to 8 hours. Praziquantel and its metabolites are mainly excreted in the urine, and within 24 hours after a single oral dose, 70 to 80% are found in urine, but less than 0.1% are found as the unchanged drug. Praziquantel is metabolized through the cytochrome P450 pathway 3A4. Agents that induce or inhibit Cyp450 3A4 (ie phenytoin, rifampin, azole antifungals) will have an effect the metabolism of praziquantel.

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 parasite cells (certain schistosomes) for 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 — focal disintegrations and disturbances of oviposition (laying of eggs) — are seen in other types of sensitive parasites.

Another hypothesis on 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 de novo.

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 preexisting 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 colicky. 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 Counts.
• Other locations/Body as a whole: Lower back pain, myalgia, arthralgia, fever, sweating, various cardiac arrhythmias, and hypotension.

Dosage

According to special dosing schedules for each different indication. Sometimes one single dose or a one-day treatment with divided doses may be sufficient.

Brand names

• Biltricide® (Bayer) 600mg Tablets
• Cesol® Tablets
• Cysticide® Tablets
• Profender® (Bayer) for veterinary use
• Droncit® (Bayer) for veterinary use
• D-Worm™ (Farnum) for veterinary use
• Tape Worm Tabs™ (Trade Winds) for veterinary use
• Cestoved® (Vedco) both tablets and injectable for veterinary use
• PraziPro™ (Hikari®) for aquarium use

External references

• AHFS Database