Chemistry:Praziquantel

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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.[1] In humans specifically, it is used to treat schistosomiasis, clonorchiasis, opisthorchiasis, tapeworm infections, cysticercosis, echinococcosis, paragonimiasis, fasciolopsiasis, and fasciolosis.[1] It should not be used for worm infections of the eye.[2] It is taken by mouth.[1]

Side effects in humans may include poor coordination, abdominal pain, vomiting, headache, and allergic reactions.[2] While it may be used during pregnancy, it is not recommended for use during breastfeeding.[2] Praziquantel is in the anthelmintic class of medications.[1] It works partly by affecting the function of the worm's sucker.[1]

Praziquantel was approved for medical use in the United States in 1982,[1] and in the European Union in April 2025.[3][4] It is on the World Health Organization's List of Essential Medicines.[5]

Medical uses

Praziquantel is used to treat diseases caused by infection with several types of internal/gastrointestinal, and external parasites, including:

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.[24]

  • Central nervous system (CNS): 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. All patients with cerebral cysticercosis are strongly recommended to be hospitalized during treatment.
  • Gastrointestinal tract: About 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. Praziquantel also has a bitter taste that can result in gagging or vomiting.[25]
  • Liver: Asymptomatic and transient increases of liver enzymes (AST and ALT) are noted frequently (up to 27%). No case of symptomatic liver damage has 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

Pregnancy

The WHO states praziquantel is safe during pregnancy (although does not recommend use during the first trimester).[26][27] Animal studies have failed to reveal evidence of fetal harm. Praziquantel is effective in reducing schistosomiasis during pregnancy.[28] Another trial found that treatment with praziquantel did not increase the rates of low birthweight, fetal death, or congenital anomalies.[29]

Drug interactions

Co-administration of drugs that inhibit the activity of drug metabolizing liver enzymes such as (CYP450), e.g., cimetidine[30], ketoconazole, itraconazole, erythromycin, and ritonavir, may increase plasma concentrations of praziquantel.[31]

The antibiotic rifampicin, a strong CYP450 inducer, decreases plasma concentrations of praziquantel.[32]

Carbamazepine and phenytoin are reported to reduce the bioavailability of praziquantel.[33] Chloroquine also reduces its bioavailability.[34]

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.[35] 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.[36]

Praziquantel is administered as a racemate; the (R)-enantiomer has greater antiparasitic activity than the (S)-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.[37]

Praziquantel is not effective against juvenile (3-4 week post-infection) mammalian-stage schistosomes, a property that has implications for efficacy and timing of drug treatment.[38]

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.[39] TRPMPZQ is a voltage-independent channel that is a member of the TRPM family of the TRP ion channel superfamily.[40][41] The active (R)-enantiomer of praziquantel activates Schistosoma mansoni TRPMPZQ with an EC50 of 597 nM (154 nM at 37°C); the EC50 for the less biologically active (S)-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.[39] The physiological role of TRPMPZQ in the parasite is currently unknown.[39]

Interestingly, the inactive (S)-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 (the interaction with TRPM8 may as well be responsible for the unpleasant taste of the drug).[42]

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.[43] 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.[44][45] Another hypothesis for praziquantel mode of action is that it interferes with adenosine uptake in schistosomes.[46] This effect may have therapeutic relevance given that schistosomes, as well as Taenia and the Echinococcus (other praziquantel-sensitive parasites), are unable to synthesize purines, such as adenosine, de novo.[47]

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."[48][49]

Pharmacokinetics

Praziquantel is well absorbed (about 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 score B and C), 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.[31][50]

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.[15]

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.[51]

Society and culture

Brand names

  • Biltricide (Bayer) Tablets (for human use)[52]
  • Cesol (Merck) Tablets
  • Cestoved (Vedco) both tablets and injectable for veterinary use
  • Cysticide (Merck) Tablets
  • Distocide (Shin Poong Pharm. Co., Ltd.) tablet (for human use)
  • Distoside (Chandra Bhagat Pharma Pvt Ltd) tablet (for human use)
  • 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.
  • Fish Tapes (Thomas Labs) for aquarium use
  • Interceptor Plus chewable tablets (combination with milbemycin) (Elanco) for veterinary use. Note regular Interceptor only has milbemycin and does not contain praziquantel.
  • Kaicide (Taiwan)
  • Milbemax (combination with milbemycin oxime) (Novartis) for veterinary use
  • Popantel (Jurox)
  • PraziPro (Hikari) for aquarium use
  • Praz-Tastic (NFP/National Fish Pharmaceuticals) for aquarium use
  • Pure Prazi (COTS Koi/Children of the Sun Koi) for aquarium use
  • PraziPure (J.K.O., Inc. d/b/a Kodama Koi Farm & Kodama Koi Garden; licensed by COTS Koi) for aquarium use
  • Profender (combination with emodepside) (Bayer) for veterinary use
  • Tape Worm Tabs (Trade Winds) for veterinary use
  • Zentozide (Berich (Thailand) Co)

Regulatory approval

Praziquantel is on the World Health Organization's List of Essential Medicines.[5]

Praziquantel is not licensed for use in humans in the UK, but it can be imported when necessary on a named-patient basis.[53] 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.[54]

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.[3] The applicant for this veterinary medicinal product is Vethellas S.A.[3] The main benefit of Prazivetin is its efficacy against infestations of the gills caused by the monogenean Sparicotyle chrysophrii.[3] Praziquantel was authorized for veterinary use in the European Union in April 2025.[3][4]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "Praziquantel". The American Society of Health-System Pharmacists. https://www.drugs.com/monograph/praziquantel.html. 
  2. ↑ 2.0 2.1 2.2 WHO Model Formulary 2008. World Health Organization. 2009. pp. 88, 593. ISBN 978-92-4-154765-9. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 "Prazivetin EPAR". 13 March 2025. https://www.ema.europa.eu/en/medicines/veterinary/EPAR/prazivetin.  Text was copied from this source which is copyright European Medicines Agency. Reproduction is authorized provided the source is acknowledged.
  4. ↑ 4.0 4.1 "Prazivetin PI". 28 April 2025. https://ec.europa.eu/health/documents/community-register/html/v340.htm. 
  5. ↑ 5.0 5.1 The selection and use of essential medicines 2023: web annex A: World Health Organization model list of essential medicines: 23rd list (2023). Geneva: World Health Organization. 2023. WHO/MHP/HPS/EML/2023.02. 
  6. ↑ "Albendazole versus praziquantel in the treatment of neurocysticercosis: a meta-analysis of comparative trials". PLOS Neglected Tropical Diseases 2 (3). March 2008. doi:10.1371/journal.pntd.0000194. PMID 18335068. 
  7. ↑ "CDC - Taeniasis - Resources for Health Professionals". 20 May 2020. https://www.cdc.gov/parasites/taeniasis/health_professionals/index.html. 
  8. ↑ "CDC - Diphyllobothrium - Resources for Health Professionals". 20 May 2020. https://www.cdc.gov/parasites/diphyllobothrium/health_professionals/index.html. 
  9. ↑ "CDC - Hymenolepis - Resources for Health Professionals". 20 May 2020. https://www.cdc.gov/parasites/hymenolepis/health_professionals/index.html. 
  10. ↑ "CDC - DPDx - Bertiella infection - Treatment Information". 29 November 2013. https://www.cdc.gov/dpdx/bertiella/tx.html. 
  11. ↑ 11.0 11.1 11.2 Drontal Data Sheet; Drontal Cat & Cat XL Film-coated Tablets, Bayer plc, Newbury, England: Bayer plc, Animal Health Division, p. 2, https://www.drontal.com/static/drontal/DrontalCat&CatXLFilm-coatedTablets.pdf, retrieved 23 September 2015 
  12. ↑ 12.0 12.1 Feline clinical parasitology (First ed.). Ames, Iowa: Iowa State University. 2002. p. 275. ISBN 978-0-8138-0333-3. https://books.google.com/books?id=mvpsA9dGdpAC&q=%22toxocara+cati%22&pg=PA278. 
  13. ↑ "Efficacy of praziquantel against Schistosoma haematobium infection in children". The American Journal of Tropical Medicine and Hygiene 71 (6): 778–782. December 2004. doi:10.4269/ajtmh.2004.71.778. PMID 15642971. 
  14. ↑ CDC (2025-01-31). "Clinical Care of Schistosomiasis" (in en-us). https://www.cdc.gov/schistosomiasis/hcp/treatment/index.html. 
  15. ↑ 15.0 15.1 "Schistosomiasis Control Program". http://www.cartercenter.org/health/schistosomiasis/index.html. 
  16. ↑ "Collection of Clonorchis sinensis adult worms from infected humans after praziquantel treatment". The Korean Journal of Parasitology 45 (2): 149–152. June 2007. doi:10.3347/kjp.2007.45.2.149. PMID 17570980. PMC 2526309. http://www.parasitol.or.kr/kjp/abstracts/2007_149.html. 
  17. ↑ "Opisthorchiasis - Treatment Information". 29 November 2013. https://www.cdc.gov/dpdx/opisthorchiasis/tx.html. 
  18. ↑ "CDC - Paragonimiasis - General Information - Frequently Asked Questions (FAQs)" (in en-us). 19 April 2019. https://www.cdc.gov/parasites/paragonimus/gen_info/faqs.html. 
  19. ↑ "CDC - Paragonimiasis - Resources for Health Professionals" (in en-us). 24 May 2019. https://www.cdc.gov/parasites/paragonimus/health_professionals/index.html. 
  20. ↑ "Fascioliasis and other plant-borne trematode zoonoses". International Journal for Parasitology 35 (11–12): 1255–1278. October 2005. doi:10.1016/j.ijpara.2005.07.010. PMID 16150452. 
  21. ↑ 21.0 21.1 "Neglected food-borne trematodiases: echinostomiasis and gastrodiscoidiasis". Parasitology 149 (10): 1319–1326. September 2022. doi:10.1017/s0031182022000385. PMID 35343418. 
  22. ↑ "[Anthelmintic Effects Of Various Drugs Against Metagonimiasis]". Kisaengch'unghak Chapchi. The Korean Journal of Parasitology 16 (2): 117–122. December 1978. doi:10.3347/kjp.1978.16.2.117. PMID 12902772. 
  23. ↑ "Effects of praziquantel on human intestinal flukes (Fasciolopsis buski and Heterophyes heterophyes)". Zentralblatt Fur Bakteriologie, Mikrobiologie, und Hygiene. Series A, Medical Microbiology, Infectious Diseases, Virology, Parasitology 262 (4): 542–550. November 1986. doi:10.1016/s0176-6724(86)80148-1. PMID 3799097. 
  24. ↑ "Praziquantel". Parasitology Research 90 Supp 1: S3-S9. June 2003. doi:10.1007/s00436-002-0751-z. PMID 12811543. 
  25. ↑ "The little we know about the pharmacokinetics and pharmacodynamics of praziquantel (racemate and R-enantiomer)". The Journal of Antimicrobial Chemotherapy 69 (4): 863–870. April 2014. doi:10.1093/jac/dkt491. PMID 24390933. 
  26. ↑ "WHO } Guideline". https://www.who.int/schistosomiasis/strategy/en/. 
  27. ↑ "WHO } Strategy". https://www.ncbi.nlm.nih.gov/books/NBK578392/pdf/Bookshelf_NBK578392.pdf. 
  28. ↑ "Effect of praziquantel treatment of Schistosoma mansoni during pregnancy on intensity of infection and antibody responses to schistosome antigens: results of a randomised, placebo-controlled trial". BMC Infectious Diseases 9 (32). March 2009. doi:10.1186/1471-2334-9-32. PMID 19296834. 
  29. ↑ "Efficacy and safety of praziquantel for the treatment of human schistosomiasis during pregnancy: a phase 2, randomised, double-blind, placebo-controlled trial". The Lancet. Infectious Diseases 16 (2): 199–208. February 2016. doi:10.1016/S1473-3099(15)00345-X. PMID 26511959. 
  30. ↑ "Effect of cimetidine, bicarbonate and glucose on the bioavailability of different formulations of praziquantel". Arzneimittel-Forschung 45 (4): 516–518. April 1995. PMID 7779153. 
  31. ↑ 31.0 31.1 "DailyMed - BILTRICIDE- praziquantel tablet, film coated". https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=34ce1cdd-648e-4f1e-8512-bf3d4cc22eb9. 
  32. ↑ "Rifampin markedly decreases plasma concentrations of praziquantel in healthy volunteers". Clinical Pharmacology and Therapeutics 72 (5): 505–513. November 2002. doi:10.1067/mcp.2002.129319. PMID 12426514. 
  33. ↑ "Drug interactions of clinical importance. An updated guide". Drug Safety 12 (6): 393–452. June 1995. doi:10.2165/00002018-199512060-00005. PMID 8527014. 
  34. ↑ "The effect of chloroquine on the pharmacokinetics and metabolism of praziquantel in rats and in humans". Biopharmaceutics & Drug Disposition 15 (1): 33–43. January 1994. doi:10.1002/bdd.2510150103. PMID 8161714. 
  35. ↑ "Chemotherapy and Drug Resistance in Schistosomiasis and Other Trematode and Cestode Infections" (in en). Antimicrobial Drug Resistance: Mechanisms of Drug Resistance. 1. Cham: Springer International Publishing. 2017. pp. 705–734. doi:10.1007/978-3-319-46718-4_47. ISBN 978-3-319-46718-4. 
  36. ↑ "Praziquantel decreases fecundity in Schistosoma mansoni adult worms that survive treatment: evidence from a laboratory life-history trade-offs selection study". Infectious Diseases of Poverty 6 (1): 110. June 2017. doi:10.1186/s40249-017-0324-0. PMID 28622767. 
  37. ↑ "Praziquantel Fifty Years on: A Comprehensive Overview of Its Solid State". Pharmaceutics 16 (1): 27. December 2023. doi:10.3390/pharmaceutics16010027. PMID 38258039. 
  38. ↑ "Development of a Novel Compound Effective Against Juvenile, Adult, and Drug-Resistant Schistosoma Species". Pharmaceutics 17 (10): 1268. September 2025. doi:10.3390/pharmaceutics17101268. PMID 41155906. 
  39. ↑ 39.0 39.1 39.2 "Progress interrogating TRPMPZQ as the target of praziquantel". PLOS Neglected Tropical Diseases 18 (2). February 2024. doi:10.1371/journal.pntd.0011929. PMID 38358948. 
  40. ↑ "TRP (transient receptor potential) ion channel family: structures, biological functions and therapeutic interventions for diseases". Signal Transduction and Targeted Therapy 8 (1). July 2023. doi:10.1038/s41392-023-01464-x. PMID 37402746. 
  41. ↑ "TRP channels". Annual Review of Biochemistry 76 (1): 387–417. 2007. doi:10.1146/annurev.biochem.75.103004.142819. PMID 17579562. Bibcode: 2007ARBio..76..387V. 
  42. ↑ "The Molecular Drug Target of Praziquantel" (in en). Praziquantel: Discovery and Development of an Anthelmintic Drug. Cham: Springer Nature Switzerland. 2026. pp. 85–105. doi:10.1007/978-3-031-97397-0_5. ISBN 978-3-031-97397-0. 
  43. ↑ "Voltage-gated calcium channel subunits from platyhelminths: potential role in praziquantel action". International Journal for Parasitology 36 (6): 625–632. May 2006. doi:10.1016/j.ijpara.2006.02.002. PMID 16545816. 
  44. ↑ "Pharmacology and potential physiological significance of schistosome multidrug resistance transporters". Experimental Parasitology 132 (1): 2–6. September 2012. doi:10.1016/j.exppara.2011.03.004. PMID 21420955. 
  45. ↑ "Schistosome ABC multidrug transporters: From pharmacology to physiology". International Journal for Parasitology. Drugs and Drug Resistance 4 (3): 301–309. December 2014. doi:10.1016/j.ijpddr.2014.09.007. PMID 25516841. 
  46. ↑ "The anti-schistosomal drug praziquantel is an adenosine antagonist". Parasitology 134 (Pt 9): 1215–1221. August 2007. doi:10.1017/S0031182007002600. PMID 17428352. 
  47. ↑ "Purinergic signaling in schistosomal infection". Biomedical Journal 39 (5): 316–325. October 2016. doi:10.1016/j.bj.2016.06.006. PMID 27884378. 
  48. ↑ "Archived copy". http://bayer.naccvp.com/view_label.php. 
  49. ↑ "Resolution of praziquantel". PLOS Neglected Tropical Diseases 5 (9). September 2011. doi:10.1371/journal.pntd.0001260. PMID 21949890. 
  50. ↑ "Drug metabolism and pharmacokinetics of praziquantel: A review of variable drug exposure during schistosomiasis treatment in human hosts and experimental models". PLoS Neglected Tropical Diseases 14 (9). September 2020. doi:10.1371/journal.pntd.0008649. PMID 32976496. 
  51. ↑ "Praziquantel". Advances in Pharmacology and Chemotherapy. Advances in Pharmacology (Elsevier) 20: 219–238. 1984. doi:10.1016/s1054-3589(08)60268-9. ISBN 978-0-12-032920-5. PMID 6398968. 
  52. ↑ "BILTRICIDE- praziquantel tablet, film coated (NDC Code(s): 50419-747-01)". July 2015. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=34ce1cdd-648e-4f1e-8512-bf3d4cc22eb9. 
  53. ↑ "Antihelmintics - Medicines for Worms; threadword, roundworm". Patient. http://patient.info//health/antihelmintics-medicines-for-worms. 
  54. ↑ Goodman and Gilman's The Pharmacological Basis of Therapeutics, Twelfth Edition (12 ed.). New York: McGraw-Hill Education / Medical. 10 January 2011. ISBN 978-0-07-162442-8. 
  55. ↑ "Treatment of fish parasites. 2. Effects of praziquantel, niclosamide, levamisole-HCl, and metrifonate on monogenea (Gyrodactylus aculeati, Diplozoon paradoxum)". Parasitology Research 73 (4): 341–351. 1987. doi:10.1007/bf00531089. PMID 3615395. 



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