Praziquantel


Praziquantel, sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat schistosomiasis, clonorchiasis, opisthorchiasis, tapeworm infections, cysticercosis, echinococcosis, paragonimiasis, fasciolopsiasis, and fasciolosis. It should not be used for worm infections of the eye. It is taken by mouth.
Side effects in humans may include poor coordination, abdominal pain, vomiting, headache, and allergic reactions. While it may be used during pregnancy, it is not recommended for use during breastfeeding. Praziquantel is in the anthelmintic class of medications. It works partly by affecting the function of the worm's sucker.
Praziquantel was approved for medical use in the United States in 1982, and in the European Union in April 2025. It is on the World Health Organization's List of Essential Medicines.

Medical uses

Praziquantel is used to treat diseases caused by infection with several types of internal/gastrointestinal, and external parasites, including:
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.
The WHO states praziquantel is safe during pregnancy. Animal studies have failed to reveal evidence of fetal harm. Praziquantel is effective in reducing schistosomiasis during pregnancy. Another trial found that treatment with praziquantel did not increase the rates of low birthweight, fetal death, or congenital anomalies.

Drug interactions

Co-administration of drugs that inhibit the activity of drug metabolizing liver enzymes such as, e.g., cimetidine, ketoconazole, itraconazole, erythromycin, and ritonavir, may increase plasma concentrations of praziquantel.
The antibiotic rifampicin, a strong CYP450 inducer, decreases plasma concentrations of praziquantel.
Carbamazepine and phenytoin are reported to reduce the bioavailability of praziquantel. Chloroquine also reduces its bioavailability.

Mechanism of action

Experimental evidence indicates praziquantel increases the permeability of the membranes of schistosome cells towards calcium ions. The drug thereby induces contraction of the parasites' muscle, resulting in paralysis in the contracted state. Another early effect of praziquantel on schistosomes is morphological disruption of the tegumental surface of the worm, exposing parasite antigens to the host immune system, and likely rendering the parasite more susceptible to host immune attack. 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. Additional mechanisms including focal disintegrations and disturbances of oviposition are seen in other types of sensitive parasites.
Praziquantel is administered as a racemate; the -enantiomer has greater antiparasitic activity than the -enantiomer, both in vitro and in vivo; the enantiomers may be separated using a resolution of an amine obtained from praziquantel, as well as by other methods.
Praziquantel is not effective against juvenile mammalian-stage schistosomes, a property that has implications for efficacy and timing of drug treatment.
The primary molecular target of the drug appears to be TRPMPZQ, a Ca2+-permeable transient receptor potential (TRP) ion channel that is found in schistosomes and other praziquantel-sensitive platyhelminths. TRPMPZQ is a voltage-independent channel that is a member of the TRPM family of the TRP ion channel superfamily. The active -enantiomer of praziquantel activates Schistosoma mansoni TRPMPZQ with an EC50 of 597 nM ; the EC50 for the less biologically active -enantiomer is 27.9 μM. TRPMPZQ is also found in the praziquantel-insensitive liver fluke, Fasciola hepatica, but exhibits a critical amino acid change in the praziquantel binding pocket from asparagine to threonine, resulting in insensitivity to activation of the channel by praziquantel. Schistosomes selected for diminished sensitivity to praziquantel exhibit reduced levels of TRPMPZQ expression. The physiological role of TRPMPZQ in the parasite is currently unknown.
Interestingly, the inactive -enantiomer of praziquantel activates a human TRPM8 channel, and it has been suggested that this interaction may enhance a praziquantel-induced elimination of schistosomes by increasing vascular contraction in host mesenteric vessels, where parasites may reside.
Although TRPMPZQ appears to be the primary target of praziquantel, it is clear that praziquantel also interacts with other targets. These include a platyhelminth-specific voltage-gated calcium channel β subunit that, when paired with an α1 subunit, results in activation of the expressed channel by 100 nM praziquantel. Praziquantel is also an inhibitor of, and a likely substrate for, a schistosome P-glycoprotein-like multidrug resistance transporter. Increased expression of this or another schistosome multidrug resistance transporter correlates with reduced sensitivity to praziquantel, while inhibition or knockdown of expression of these proteins increases worm responsiveness to praziquantel. Another hypothesis for praziquantel mode of action is that it interferes with adenosine uptake in schistosomes. This effect may have therapeutic relevance given that schistosomes, as well as Taenia and the Echinococcus, are unable to synthesize purines, such as adenosine, de novo.
Bayer's Animal Health Division website states, "Praziquantel is active against cestodes. 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, 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."

Pharmacokinetics

Praziquantel is well absorbed 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, the serum half-life is increased to 3 to 8 hours. Praziquantel and its metabolites are mainly excreted renally; within 24 h 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.

History

Praziquantel was developed in the laboratories for parasitological research of Bayer AG and Merck KGaA in Germany in the mid-1970s.

Society and culture

Brand names

  • Biltricide Tablets
  • Cesol Tablets
  • Cestoved both tablets and injectable for veterinary use
  • Cysticide Tablets
  • Distocide tablet
  • Distoside tablet
  • Droncit for veterinary use
  • Drontal for veterinary use
  • D-Worm for veterinary use; note that D-Worm also makes roundworm medicine containing piperidine which is not effective against tapeworms.
  • Fish Tapes for aquarium use
  • Interceptor Plus chewable tablets for veterinary use. Note regular Interceptor only has milbemycin and does not contain praziquantel.
  • Kaicide
  • Milbemax for veterinary use
  • Popantel
  • PraziPro for aquarium use
  • Praz-Tastic for aquarium use
  • Pure Prazi for aquarium use
  • PraziPure for aquarium use
  • Profender for veterinary use
  • Tape Worm Tabs for veterinary use
  • Zentozide

    Regulatory approval

Praziquantel is on the World Health Organization's List of Essential Medicines.
Praziquantel is not licensed for use in humans in the UK, but it can be imported when necessary on a named-patient basis. It is available in the UK as a veterinary anthelmintic.
Praziquantel is approved in the US for the treatment of schistosomiasis and liver flukes, although it is effective in other infections.

Veterinary medicine

In March 2025, the Committee for Veterinary Medicinal Products of the European Medicines Agency adopted a positive opinion, recommending the granting of a marketing authorization for the veterinary medicinal product 'Prazivetin premix for medicated feeding stuff' intended for sea bream. The applicant for this veterinary medicinal product is Vethellas S.A. The main benefit of Prazivetin is its efficacy against infestations of the gills caused by the monogenean Sparicotyle chrysophrii. Praziquantel was authorized for veterinary use in the European Union in April 2025.