VA Class:AP200
Praziquantel is a synthetic anthelmintic agent2, 3, 4, 5 that is structurally unrelated to other currently available anthelmintic agents.5
Praziquantel is used for the treatment of schistosomiasis (bilharziasis) caused by all Schistosoma species pathogenic to humans.1, 14, 15, 16, 17, 18, 19, 20, 21, 24, 25, 26, 27, 28, 29, 30, 32, 33, 34, 35, 38, 40, 41, 42, 55, 56, 87, 88, 89, 128, 133, 134, 140 The drug has been used effectively for the treatment of individual patients3, 9, 12, 14, 16, 17, 21, 140 and in mass-treatment and control programs.3, 6, 9, 12, 15, 18, 19, 20, 89
Praziquantel is effective against all stages of Schistosoma infection including the acute phase3, 6, 9, 12, 14, 15, 17, 18, 19, 20, 140 and the chronic phase (which may be associated with hepatosplenic involvement).9, 12, 15, 16, 21, 27, 30, 81 The drug appears to be effective in the treatment of severe schistosomiasis (e.g., neuroschistosomiasis); however, to prevent substantial morbidity and long-term sequelae (e.g., paraplegia, persistent impotence) associated with this condition, therapy with praziquantel must be initiated promptly.140, 141 Drug therapy may be initiated in patients with suspected neuroschistosomiasis pending the results of confirmative tests.141 Adult schistosomes do not multiply within the human host; therefore, the worm load depends on the intensity and frequency of infection and the life-span of the worm.12, 38, 49, 50 Mature schistosomes constantly produce eggs, most of which are retained in host tissues eliciting an immunologic granulomatous response and tissue injury and scarring.12, 38, 49, 50, 51 The severity of disease is related to the intensity of infection.12, 38, 49, 50 Efficacy of antischistosomal drugs results from markedly reducing the worm load and thus preventing production of eggs.12, 38, 49, 50
Praziquantel has produced cure rates of 75-95% and/or egg reduction percentages of 80-98% in patients with schistosomiasis3, 4, 6, 9, 14, 15, 16, 17, 18, 19, 20, 21, 24, 27, 28, 29, 30, 32, 33, 34, 35, 38, 40, 41, 42, 89, 128, 133 and is considered the drug of choice for the treatment of infections caused by S. haematobium , S. japonicum , S. mansoni , or S. mekongi ;3, 4, 6, 9, 11, 14, 15, 16, 29, 32, 33, 34, 38, 55, 87, 88, 89, 128, 133, 134 the drug is the only currently available anthelmintic shown to be effective in the treatment of infections caused by S. intercalatum †11 or S. mekongi .4, 11, 87 Oxamniquine (no longer commercially available in the US) is considered an alternative to praziquantel in the treatment of infections caused by S. mansoni 4, 11, 55, 56, 87, 88, 133, 134 and may be effective in some areas in which praziquantel is less effective.134 Praziquantel has replaced niridazole or antimony salts (drugs not commercially available in the US) for the treatment of S. japonicum 4 infections because of decreased toxicity and increased efficacy.4, 65, 89 The efficacy of praziquantel in the treatment of schistosomiasis may vary as a function of patient age6, 38 and the degree of infection.6 Cure rates generally are lower in children6, 38 and in patients with massive infections.6
Travelers to endemic areas of the Caribbean, South America, Africa, Middle East, and Asia are at risk for schistosomiasis.56 Because there is no practical way for travelers to distinguish between infested and noninfested water, fresh-water wading or swimming in rural areas of endemic countries should be avoided.56 Outbreaks of schistosomiasis have occurred among adventure travelers participating in river trips in Africa as well as resident expatriates and Peace Corps volunteers in high-risk areas.56 Those at greatest risk are travelers who engage in wading, swimming, or bathing in fresh water in areas where poor sanitation and appropriate snail hosts are present.56
To minimize the risk of morbidity associated with delayed recognition of schistosomal infections, the US Centers for Disease Control and Prevention (CDC) recommends that travelers and expatriates with a history of fresh-water exposure (e.g., recreational) returning from Schistosoma -endemic areas undergo screening tests for the infection.56, 140 Because serologic tests can be more sensitive than microscopic examination of stool and urine for eggs, previously uninfected but potentially exposed travelers should be tested for antibodies to schistosomes if microscopic examination of stool and urine is negative or not available.56 Serologic tests available from the CDC may be more sensitive and specific than commercially available tests,56 and may be particularly helpful for detecting light infections or before eggs appear in stool or urine.55 Following thorough clinical evaluation, seropositive individuals should receive praziquantel therapy.140, 141 The possibility of neuroschistosomiasis should be suspected in any individual with CNS abnormalities who has returned from endemic areas.140, 141 Such infections can occur several months after exposure to infested water, and eggs may be undetectable or difficult to identify in urine and stool.140, 141 Presumptive praziquantel therapy should be initiated promptly whenever a strong suspicion of infection exists and should not be delayed pending confirmatory tests.140, 141
Clonorchiasis and Opisthorchiasis
Praziquantel is used for the treatment of clonorchiasis caused by Clonorchis sinensis (Chinese liver fluke)1, 3, 4, 9, 11, 22, 25, 26, 31, 43, 87, 88, 90, 91, 92, 93, 102, 103, 104, 105, 118, 119, 128, 129, 134 and opisthorchiasis caused by Opisthorchis viverrini (Southeast Asian liver fluke).1, 3, 4, 9, 11, 25, 26, 29, 44, 87, 94, 95, 96, 97, 102, 104, 105, 118, 119, 126, 128, 130, 131, 132, 134 Praziquantel has produced a cure rate of 86-98% in patients with clonorchiasis or opisthorchiasis31, 126, 128, 129, 130 and currently is considered the drug of choice for the treatment of these infections.87, 88, 128, 130, 134
Praziquantel has been effective and is considered the drug of choice55, 87, 88, 134 for the treatment of other trematode (fluke) infections, including those caused by Fasciolopsis buski † (intestinal fluke),11, 87, 88, 107 Heterophyes heterophyes † (intestinal fluke),11, 87 Metagonimus yokogawai † (intestinal fluke),9, 11, 106 Metorchis conjunctus † (North American liver fluke), Nanophyetus salmincola † (formerly Troglotrema salmincola ) (intestinal fluke),135, 136 and Paragonimus westermani † (lung fluke).3, 4, 9, 11, 37, 55, 88, 98, 99, 100, 101
Praziquantel has been used in a limited number of patients for infections caused by Fasciola hepatica † (sheep liver fluke),87, 108 but the drug was inactive against the trematode in vitro in one study109 and treatment failures have been reported.88, 110, 134 Some clinicians recommend triclabendazole (not commercially available in the US) as the drug of choice and bithionol (not commercially available in the US; may be available from the CDC) or nitazoxanide as alternatives for the treatment of these infections.134, 146
Praziquantel also has been effective in a limited number of patients with infections caused by P. kellicotti † (American lung fluke),48 P. heterotrema † (lung fluke),111 and P. uterobilateralis † (African lung fluke).71
Praziquantel has been used for the treatment of cestodiasis (tapeworm infections) caused by certain cestodes pathogenic to humans, including Diphyllobothrium latum † (fish tapeworm),2, 4, 46, 47, 134 Dipylidium caninum † (dog and cat tapeworm),46, 134 Taenia saginata † (beef tapeworm),2, 4, 46, 134 and T. solium † (pork tapeworm).4, 11, 46, 87, 134, 142, 143, 144, 145 Praziquantel is considered the drug of choice and niclosamide (no longer commercially available in the US) is the alternative for treatment of infections caused by these cestodes.55, 87, 134
Praziquantel has been used for the treatment of infections caused by Hymenolepis nana † (dwarf tapeworm)2, 3, 4, 9, 11, 23, 46, 87, 134 and is considered the drug of choice for these infections;87, 134 nitazoxanide is recommended as an alternative.134
Praziquantel is effective against the adult, juvenile, and larval stages of susceptible cestodes.4, 46 Although niclosamide and paromomycin are effective for the treatment of cestodiasis caused by T. solium †, some clinicians consider praziquantel the drug of choice for this infection because niclosamide and paromomycin cause disintegration of worm segments and release of viable eggs, which may be associated with a theoretical risk for the development of cysticercosis; niclosamide is not effective against cysticerci.66, 67, 68
Praziquantel has been used for the treatment of cysticercosis†, including neurocysticercosis†, caused by the larval form of T. solium ( Cysticercus cellulosae ).3, 9, 11, 46, 52, 53, 72, 73, 74, 88, 113, 114, 115, 116, 121, 123, 124, 134
In a limited number of patients with neurocysticercosis caused by T. solium , praziquantel therapy has been shown to cause a long-term decrease in the frequency of seizures and the frequency and severity of episodes of increased intracranial pressure and has produced radiographic evidence of a reduction in the number and size of cysts.52, 53, 72, 113, 115, 116, 121, 123, 124 However, use of antiparasitic therapy in patients with neurocysticercosis, especially those with seizures, has been controversial.55, 134, 147, 148 Adverse nervous system effects (CSF reaction syndrome) occur frequently during praziquantel therapy for neurocysticercosis.52, 53, 72, 73, 74, 76, 114, 115, 116, 121 (See Cautions: Nervous System Effects.) Corticosteroids may be indicated; anticonvulsants (possibly long term) may be required.52, 55, 65, 73, 74, 76, 114, 115, 116, 121, 123, 134
Treatment of neurocysticercosis† must be individualized based on the location, number, and viability of cysticerci; specialized references should be consulted regarding current recommendations for treatment of these infections.55, 134, 147, 148 In some patients, the risks of severe adverse effects associated with antiparasitic therapy may outweigh the potential benefits.147, 148
Praziquantel has been ineffective in patients with intraocular cysticercosis†, 85, 117 and the manufacturer and some clinicians state that praziquantel should not be used in the treatment of this condition because of the risk of irreversible intraocular lesions secondary to killing of the cysts.1, 88 An ophthalmic examination should be performed to rule out intraocular cysts before use of praziquantel.55, 134
Although praziquantel has been effective in the treatment of adult Echinococcus infections in dogs, studies in rodents and sheep have failed to demonstrate any efficacy of the drug in the treatment of larval Echinococcus infections (hydatid cysts), and it is unlikely that these infections in humans will respond to the drug.4, 60, 61 Surgical resection of the cysts or, when surgery is contraindicated or the cysts rupture spontaneously during surgery, mebendazole or albendazole is currently considered the treatment of choice.83, 134 Because praziquantel can kill Echinococcus (e.g., protoscoleces),122 the drug may be useful for perioperative prophylaxis or in case of spilling of cyst contents during surgery.122, 134
Praziquantel is administered orally.1 The tablets should not be chewed but can be halved or quartered to allow administration of individualized doses.1 Patients should be instructed to immediately swallow the praziquantel tablets, halves, and/or quarters with a sufficient amount of water during meals.1 Retention of the tablets or tablet segments in the mouth may cause gagging or vomiting as a result of the drug's bitter taste.1 Some clinicians state that regurgitation during administration of the tablets may theoretically predispose the patient to the development of cysticercosis during therapy for Taenia solium † infections.65
For the treatment of schistosomiasis caused by all species of Schistosoma pathogenic to humans, the usual dosage of praziquantel recommended by the manufacturer in adults and children 4 years of age and older is 20 mg/kg 3 times daily for 1 day; the 3 doses should be given at intervals of not less than 4 hours and not more than 6 hours.1
Some clinicians recommend that adult or pediatric patients with schistosomiasis caused by Schistosoma haematobium or S. mansoni receive praziquantel in a dosage of 40 mg/kg given in 2 equally divided doses on the same day and that those with infections caused by S. japonicum or S. mekongi receive a dosage of 60 mg/kg given in 3 equally divided doses on the same day.134 Other clinicians recommend the lower dosages (40 mg/kg given as a single dose or in 2 equally divided doses) for any patient with schistosomiasis since such dosages have been effective in some patients.3, 6, 9, 12, 14, 15, 16, 17, 19, 20, 128, 133
Clonorchiasis and Opisthorchiasis
For the treatment of clonorchiasis caused by Clonorchis sinensis or opisthorchiasis caused by Opisthorchis viverrini , the usual dosage of praziquantel in adults and children 4 years of age or older is 75 mg/kg given in 3 equally divided doses on the same day.1, 11, 25, 26, 31, 43, 44, 87, 88, 90, 91, 92, 94, 95, 96, 102, 104, 105, 128, 129, 130, 134 The manufacturer recommends that the 3 doses be given at intervals of not less than 4 hours and not more than 6 hours.1
Lower dosages (40-50 mg/kg given as a single dose) have been effective in the treatment of C. sinensis or O. viverrini infections in some patients;31, 126, 131, 132 however, these dosages may be associated with lower cure rates.31
For the treatment of trematodiasis caused by Fasciolopsis buski †, 11, 87, 88, 134 Heterophyes heterophyes †, 11, 87, 134 or Metagonimus yokogawai †, 11, 87, 134 the usual dosage of praziquantel in adults and children is 75 mg/kg given in 3 equally divided doses on the same day.
For the treatment of trematode infections caused by Nanophyetus salmincola †, the usual dosage of praziquantel in adults and children is 60 mg/kg given in 3 equally divided doses on the same day.134, 135, 136
For the treatment of trematodiasis caused by Fasciola hepatica †, a dosage of 25 mg/kg 3 times daily for 5-8 days has been used in a limited number of adults and children,87 but treatment failures have occurred.88, 110, 134 (See Other Trematode Infections under Uses: Trematode [Fluke] Infections.)
For the treatment of trematode infections caused by Paragonimus westermani †, the usual dosage in adults and children is 25 mg/kg 3 times daily for 2 days.134 For the treatment of trematodiasis caused by P. uterobilateralis †, a dosage of 25 mg/kg 3 times daily for 2 days has been effective.71
For the treatment of cestodiasis caused by Diphyllobothrium latum † (fish tapeworm), Dipylidium caninum † (dog and cat tapeworm), Taenia saginata † (beef tapeworm), or T. solium † (pork tapeworm), the usual dose of praziquantel in adults and children is a single dose of 5-10 mg/kg.134
For the treatment of cestodiasis caused by Hymenolepis nana † (dwarf tapeworm), the usual dose in adults and children is a single dose of 25 mg/kg.87, 134 Eradication may be difficult; if the infection persists, retreatment with praziquantel is recommended.55
For the treatment of cysticercosis, the usual dosage of praziquantel in adults and children is 50-100 mg/kg given in 3 divided doses daily for 30 days.134
A praziquantel dosage of 50 mg/kg given in 3 equally divided doses daily for 14-21 days has been used for the treatment of neurocysticercosis†.52, 53, 72, 74, 88, 113, 115, 116, 121 Because of the risk of praziquantel-induced adverse nervous system effects in patients with neurocysticercosis (see Cautions: Nervous System Effects), corticosteroids (e.g., dexamethasone 6-24 mg daily, prednisone 30-60 mg daily) often are administered concomitantly with praziquantel.52, 65, 73, 74, 76, 121 Although the potential benefit of additional courses of praziquantel therapy in adults with neurocysticercosis has not been determined, some clinicians suggest that repeated courses of therapy may be useful in patients who show only partial resolution of cysts 3 months after a course or whose condition deteriorates.53, 121, 123
Dosage adjustments are not necessary in patients with renal impairment.1
At recommended dosage, praziquantel generally is well tolerated.1, 2, 3, 4, 10, 17, 19, 27, 28, 29, 38, 112, 128, 129 Adverse effects associated with praziquantel therapy occur frequently but usually are transient, mild to moderate in severity, and do not require treatment.1, 4, 14, 15, 16, 38, 41, 89, 90, 91, 92, 93, 94, 96, 98, 99, 104, 105, 111, 112, 126, 130 Some adverse effects associated with praziquantel therapy may be secondary to the parasitic infection being treated and/or to dead and dying parasites rather than to the drug itself,1, 52, 53, 72, 73, 74, 76, 87, 100, 112, 113, 114, 115, 116, 121, 123 and such effects may be more frequent and/or severe in patients with a heavy worm burden.1, 87, 100, 121
Adverse nervous system effects occur frequently with praziquantel; however, most of these effects are mild and transient.1, 3, 4, 14, 15, 16, 18, 19, 40, 41, 42, 89, 91, 93, 94, 112 The most frequent adverse nervous system effects of praziquantel are dizziness,1, 3, 15, 16, 19, 41, 42, 89, 90, 91, 92, 93, 94, 98, 102, 103, 104, 107, 111, 112, 126, 128 headache,1, 4, 14, 16, 19, 41, 42, 89, 90, 91, 92, 93, 94, 96, 98, 100, 102, 103, 104, 107, 111, 112, 121, 126, 128, 130 and malaise.1, 4, 104, 121, 126 Other adverse nervous system effects of praziquantel include drowsiness,14, 16, 18, 94, 96, 102, 107, 112, 126, 130 somnolence,1 and lassitude (fatigue).14, 18, 42, 90, 91, 92, 93, 94, 96, 107, 128, 130 Vertigo1 and giddiness14 also have been reported.
Adverse nervous system effects (CSF reaction syndrome), including headache, exacerbation of neurologic signs and symptoms such as seizures, increased CSF protein concentrations and anticysticercal IgG levels, arachnoiditis, meningism, hyperthermia, and intracranial hypertension52, 53, 72, 73, 74, 76, 114, 115, 116, 121, 123, 137 occur in almost all53, 74, 121 patients during praziquantel therapy for neurocysticercosis and may rarely be life-threatening.73, 114, 115, 116 The CSF reaction syndrome is thought to result from an intense inflammatory response to dead and dying larvae in the CNS52, 53, 72, 73, 74, 76, 114, 115, 116, 121, 123 and may be similar to the Jarisch-Herxheimer reaction that occurs during penicillin therapy for syphilis;52 the risk of serious reactions probably is related to the number, size, and location of viable cysts in the CNS.121 Concomitant use of corticosteroids during praziquantel therapy for neurocysticercosis reportedly substantially reduces the frequency and severity of these adverse nervous system effects.72, 73, 74, 76, 114, 115, 116, 121, 123
Adverse GI effects of praziquantel occur frequently.3, 4, 14, 15, 16, 17, 19, 38, 40, 41, 42, 89, 91, 93, 112, 126 Abdominal pain or discomfort (with or without nausea)1, 3, 4, 14, 15, 16, 17, 38, 40, 41, 42, 89, 90, 91, 93, 94, 96, 98, 100, 102, 104, 107, 108, 112, 126, 130 occurs in about 90% of patients receiving the drug. Vomiting,1, 14, 15, 16, 19, 38, 41, 42, 93, 100, 103, 107, 112 epigastric pain,90, 91, 93, 94, 107, 126 anorexia,1, 14, 90, 91, 92, 93, 94, 98, 126 urge to defecate,89 and diarrhea14, 16, 41, 91, 93, 94, 104, 107, 112, 126, 130 have also been reported. GI reactions, principally colicky, crampy abdominal pain, occasionally may be severe, occurring suddenly within 1 hour after administration of the drug; such reactions may be accompanied by fever, sweating, and bloody stools.89
Mild to moderate, transient increases in serum AST (SGOT) and/or ALT (SGPT) concentrations1 have occurred in about 3-27% of patients receiving praziquantel;16, 104 however, there has been no evidence of serious drug-induced adverse hepatic effects, even in patients with schistosomal infection associated with severe hepatosplenic involvement.1, 16, 81, 112
Urticaria,1, 14, 15, 16, 42, 93, 100, 128 rash (e.g., maculopapular),102, 103, 111, 128 and pruritus14, 15, 16, 42, 93, 102 have been reported in patients receiving praziquantel. A generalized hypersensitivity reaction, including polyserositis, also has been reported.1
Minimal increases in eosinophil count have occurred in a few patients with schistosomiasis treated with the drug;19, 40 however, eosinophilia can be associated with schistosomiasis38, 50 and may be a consequence of a host-mediated immunologic response to antigen release during drug-induced killing of the worms.65, 77, 78 Similarly, urticaria may result from an immunologic response to antigen release from the worms.100
Low back pain,91, 94, 126 myalgia or arthralgia,1, 91, 94, 96, 111, 126 asthenia,1 fever or hot sensation,1, 3, 14, 15, 16, 40, 41, 42, 89, 93, 94, 112, 126, 128 sweating,14, 89, 93, 94 palpitation,94, 111, 126 arrhythmia (including bradycardia, ectopic rhythms, ventricular fibrillation, AV blocks),1 and hypotension103 have been reported in some patients receiving praziquantel. Although praziquantel has been shown to induce a positive inotropic effect on rat atria in vitro,2 this effect has not been reported to date in humans receiving the drug and the clinical importance of this finding has not been determined.
Precautions and Contraindications
Praziquantel is contraindicated in patients who are hypersensitive to the drug.1
The manufacturer and some clinicians state that praziquantel is contraindicated in patients with intraocular cysticercosis† because of the risk of irreversible intraocular lesions secondary to killing of the cysts.1, 88 If praziquantel is used in the treatment of cysticercosis, an ophthalmic examination should be performed to rule out intraocular cysts.55, 134
The manufacturer states that patients with schistosomiasis who are found to have cerebral cysticercosis should be hospitalized for the duration of treatment.134 Use of praziquantel in patients with neurocysticercosis is controversial. (See Uses: Cestode [Tapeworm] Infections.)
Patients should be warned that praziquantel may impair their ability to perform activities requiring mental alertness or physical coordination (e.g., operating machinery, driving a motor vehicle) and, therefore, the manufacturer recommends that patients not perform such activities on the day of, and the day following, praziquantel therapy.1 Some clinicians state that praziquantel should be used with caution in patients with a history of seizures.137
Patients with cardiac irregularities should be monitored during praziquantel treatment.1
Praziquantel should be used with caution in hepatosplenic patients with schistosomiasis who have moderate to severe liver impairment (Child-Pugh class B and C).1 Hepatic metabolism of praziquantel may be decreased in these patients, resulting in considerably higher and more prolonged plasma concentrations of unchanged drug.
Safety of praziquantel in children younger than 4 years of age has not been established.1
Clinical studies evaluating praziquantel did not include sufficient numbers of individuals 65 years of age and older to determine whether they respond differently from younger adults.1 Other reported clinical experience has not identified differences in responses between geriatric adults and younger patients, but greater sensitivity in some older patients cannot be ruled out.1 Because praziquantel is substantially eliminated by the kidneys and because older patients are more likely to have decreased renal function, the risk of toxicity may be greater in geriatric patients.1
Mutagenicity and Carcinogenicity
It is not known whether praziquantel is mutagenic or carcinogenic in humans.65, 80 Although praziquantel has been reported by one laboratory to be mutagenic in bacteria,1, 86 these results have not been reproducible, and other studies have not shown the drug to be mutagenic in bacteria or mammalian cells.1, 10, 64, 82, 86 The drug has been shown to act as a comutagen, increasing the mutagenicity of several mutagenic and/or carcinogenic chemicals in vitro in bacteria and animal cells.79 No evidence of carcinogenesis was seen in animals receiving oral praziquantel dosages up to 250 mg/kg once weekly for 2 years.10
Pregnancy, Fertility, and Lactation
Reproduction studies in rats and rabbits using praziquantel dosages up to 40 times the usual human dosage have not revealed evidence of harm to the fetus.1, 82, 86 An increase in the rate of spontaneous abortion occurred in rats following administration of praziquantel dosages 3 times the usual human dosage.1 There are no adequate and controlled studies to date using praziquantel in pregnant women, and the drug should be used during pregnancy only when clearly needed.1
It is not known whether praziquantel affects fertility in humans.65, 80 Reproduction studies in rats and rabbits using praziquantel dosages up to 40 times the usual human dosage have not revealed evidence of impaired fertility.1, 10, 86
Since praziquantel is distributed into milk, women should temporarily discontinue nursing on the day of praziquantel therapy and for 72 hours after administration of the last dose of the drug.1
Drugs Affecting or Metabolized by Hepatic Microsomal Enzymes
Pharmacokinetic interactions are likely with drugs that are inhibitors, inducers, or substrates of cytochrome P-450 (CYP) isoenzymes with possible alterations in metabolism and concentrations of praziquantel and/or the other drug.1
Concomitant use of praziquantel and drugs that increase the activity of CYP isoenzymes (e.g., carbamazepine, dexamethasone, phenytoin, phenobarbital) may reduce plasma concentrations of praziquantel.1 Conversely, concomitant use of praziquantel and drugs that decrease the activity of CYP isoenzymes (e.g., cimetidine, erythromycin, itraconazole, ketoconazole) may increase plasma concentrations of praziquantel.1
Concomitant use of rifampin and praziquantel should be avoided; rifampin is a strong inducer of CYP isoenzymes and may cause subtherapeutic concentrations of the anthelmintic.1
Concomitant use of chloroquine and praziquantel may result in decreased praziquantel concentrations.1 The mechanism of this drug interaction is unclear.1
Grapefruit juice is reported to produce an increase in peak plasma concentrations and area under the concentration-time curve (AUC) of praziquantel (1.6- and 1.9-fold increase, respectively).1 The importance of this increased exposure to praziquantel in relation to the drug's safety and efficacy has not been systematically evaluated.1
Although the clinical importance is unclear, limited evidence from one study in mice indicates that the antischistosomal activity of praziquantel and oxamniquine (no longer commercially available in the US) may be synergistic against Schistosoma mansoni when the two drugs are administered concomitantly.54
Limited information is available on the acute toxicity of praziquantel.
The acute lethal dose of praziquantel in humans has not been determined.1 Toxicologic studies in animals have shown that the oral LD50 of praziquantel is about 2.5 g/kg in mice,10, 86 about 2.8 g/kg in rats,10, 86 1.05 g/kg in rabbits,10, 86 and greater than 200 mg/kg in dogs;10, 86 however, an actual acute oral lethal dose could not be established in dogs because of the emetic effect of the drug in this species.10, 86
Although there has been no experience to date with acute praziquantel overdosage in humans, the manufacturer states that a fast-acting laxative should be given following acute ingestion of an overdose of the drug.1
The exact mechanism of praziquantel's activity against trematodes (flukes), including its antischistosomal activity, has not been fully elucidated.4, 5, 6, 127, 128 Praziquantel appears to directly kill susceptible adult schistosomes in vivo.6, 8, 69, 128 In addition, the drug causes the dead or dying worms to be dislodged from their usual sites of residence in the mesenteric or pelvic (e.g., vesical plexus) veins to the liver where they are retained and subsequently elicit host tissue reactions (e.g., phagocytosis).4, 5, 6, 7, 8 The dislodgment of worms appears to result principally from contraction and paralysis of their musculature and subsequent immobilization of their suckers, which causes the worms to detach from the blood vessel wall, thereby allowing passive dislodgment by normal blood flow.2, 4, 5, 6, 7, 8, 112, 128 The drug-induced contraction and subsequent paralysis in the contracted state appear to result from an increased permeability of the cell membrane of susceptible worms to calcium and consequent influx of calcium ions.1, 2, 4, 5, 7, 128 Evidence from studies in animals with schistosomal infections indicates that praziquantel is readily taken up by schistosomes and that the drug-induced dislodgment of schistosomes to the liver is rapid, occurring within 1 hour after administration of a single oral dose;4, 5, 7 contraction and paralysis of the worms occur almost immediately2, 5, 7, 112 but may be reversible at subtherapeutic plasma praziquantel concentrations (less than 0.3 mcg/mL).2, 5
Following administration of praziquantel, intense, focal vacuolization and subsequent disintegration at distinct sites of the schistosomal integument occur.1, 2, 4, 5, 7, 69, 70, 109, 112, 128 Vacuolization and disintegration of the integument result in formation of a defect in the surface of the worms and cause most schistosomes to lose their normal copulatory position, thus substantially reducing oviposition (laying of eggs).7 Evidence from animal studies indicates that praziquantel-induced vacuolization of schistosomal integument begins within 15 minutes following administration of the drug and that after 1 day the integument is largely destroyed where vacuolization has occurred;7, 70 eosinophilic granulocytes from the definitive host attach to the vacuolized regions and subsequently infiltrate the interior of the schistosomes resulting in a progressive internal lysis.7 Male Schistosoma mansoni worms appear to be more susceptible than females;7, 69, 70 however, evidence from studies in animals with schistosomal infections caused by S . mansoni indicates that all worms were dead 7 days following treatment with the drug.7 The number of worms affected and the degree of integumental injury appear to be dose related; in addition, the degree of injury increases with time posttreatment.69 Limited evidence in animals suggests that female S . haematobium worms may be more susceptible than males.8
Studies in animals with experimentally induced schistosomal infections indicate that praziquantel is active against all developmental stages of schistosomes including the miracidia and cercariae (the free-swimming larvae that emerge from the intermediate snail host).5
The exact mechanism of praziquantel's activity against other trematodes also has not been fully characterized; however, the drug has been shown to cause focal vacuolization and subsequent disintegration at distinct sites of these worms similar to the effects induced by the drug in schistosomes.57 In addition, studies using Opisthorchis viverrini indicate that praziquantel increases permeability of the liver fluke tegument to calcium, presumably by interfering with the mechanism that regulates calcium binding or transport across the tegumental membrane.127
Although the exact mechanism of praziquantel's activity against cestodes (tapeworms) has not been determined, the drug generally does not kill susceptible adult cestodes in vivo, but causes the worms to be dislodged from their usual sites of residence in the intestine.2 The dislodgment of the worms appears to result from drug-induced impairment of the function of the worms' suckers.2 The effects of praziquantel against cestodes is concentration dependent in vitro.2 At low concentrations (1-10 ng/mL) in vitro, the drug stimulates cestode motility and impairs the function of their suckers.2 As the in vitro concentration of the drug increases (10-100 ng/mL), contraction of the strobila (chain of proglottids) occurs and, at high concentrations (greater than 1000 ng/mL), instantaneous, irreversible contraction of the strobila occurs.2 Praziquantel also causes irreversible focal vacuolization and subsequent disintegration at specific sites of the cestodal integument.2, 62, 63 The characteristic integumental lesions are restricted to the growth zone of the neck region; the proglottids of the central and posterior portions of the strobila are not affected.63
Praziquantel has a broad spectrum of anthelmintic activity.3, 4, 10, 11, 12, 38 The drug has activity against many trematodes, including schistosomes, and also has activity against many cestodes.3, 4, 10, 11, 12, 38
Praziquantel is active against all Schistosoma species pathogenic to humans,4, 9, 10, 11, 12, 38 including S. mansoni ,3, 4, 5, 7, 8, 9, 11, 14, 15, 16, 29, 32, 33, 34, 38, 109 S. haematobium ,3, 4, 5, 6, 8, 9, 11, 17, 18, 19, 20, 27, 34, 38 S. japonicum ,3, 4, 5, 6, 8, 9, 11, 28, 30 S. mekongi ,3, 11, 21, 35 and S . intercalatum .10, 11, 12, 24 In vitro, susceptible schistosomes are rapidly killed by praziquantel concentrations of 0.3 mcg/mL and greater.6
Praziquantel has also been shown to be active against other trematodes, including the liver flukes Clonorchis sinensis ,3, 4, 9, 11, 22, 25, 26, 31, 43 Opisthorchis viverrini ,3, 4, 9, 11, 25, 26, 44 and Fasciola hepatica ; the lung flukes Paragonimus westermani ,3, 4, 9, 11, 37 P . uterobilateralis ,71 and P . kellicotti ;48 and the intestinal flukes Metagonimus yokogawai ,9, 11 Nanophyetus salmincola (formerly Troglotrema salmincola ),135, 136, 138, 139 Fasciolopsis buski ,11 and Heterophyes heterophyes .11
Praziquantel has been shown to be active against adult, juvenile, and larval stages of certain cestodes (tapeworms) pathogenic to humans including Diphyllobothrium latum (fish tapeworm),2, 4, 46, 47 Dipylidium caninum (dog and cat tapeworm),46 Hymenolepis nana (dwarf tapeworm),2, 3, 4, 9, 11, 23, 46 Taenia saginata (beef tapeworm),2, 4, 46 T . solium (pork tapeworm),3, 4, 9, 11, 46 and Cysticercus cellulosae (larval or tissue stage of T . solium ).3, 9, 46
Praziquantel is well absorbed following oral administration.1, 2, 9, 10, 36 Approximately 80% of an oral dose of the drug is absorbed from the GI tract;1, 9, 36 however, because of extensive first-pass metabolism, only a small portion reaches systemic circulation as unchanged praziquantel.4, 9, 10, 36
Peak serum concentrations of praziquantel occur approximately 1-3 hours after oral administration of usual doses of the drug.1, 2, 4, 9, 10, 36 Following oral administration of a single 50-mg/kg dose in healthy adults in one study, peak serum drug concentrations of about 1 mcg/mL occurred at 1-2 hours.36
Distribution of praziquantel into human body tissues and fluids has not been fully characterized.65, 80 In studies in rats, concentrations of free (unbound) praziquantel in CSF were similar to those in serum.4, 49 The concentration of the drug in CSF is reported to be 14-20% of the concurrent total (free plus protein-bound) plasma concentration.4
Praziquantel is distributed into milk in concentrations about 25% of maternal serum concentrations.1, 36, 112
Praziquantel has a serum half-life of about 0.8-1.5 hours1, 2, 4, 36 in adults with normal renal and hepatic function;4, 36 however, the serum half-life of metabolites of the drug is about 4-5 hours.4, 36
Although the exact metabolic fate of praziquantel is not clearly established, the drug is rapidly and extensively metabolized, principally in the liver via hydroxylation to monohydroxylated and polyhydroxylated metabolites.4, 36 It is not known if these metabolites possess anthelmintic activity.65, 80
Results of a study in patients with Schistosoma mansoni infections indicate that the pharmacokinetics of praziquantel in patients with normal hepatic function or mild hepatic impairment (Child-Pugh class A) are similar, but the half-life, peak serum concentrations, and area under the concentration-time curve (AUC) are increased in patients with moderate to severe hepatic dysfunction (Child-Pugh class B and C).1 In these infected patients, the half-life of the drug was about 3 hours in those with normal renal function, about 4.6 hours in those with mild or moderate hepatic impairment (Child-Pugh class A or B), and about 8.5 hours in those with severe hepatic impairment (Child-Pugh class C).1
Praziquantel and its metabolites are excreted mainly in urine.1, 2, 4, 36 Following a single oral dose of the drug, approximately 70-80% of the dose is excreted in urine within 24 hours, principally as metabolites;4, 36 less than 0.1% of an oral dose is excreted in urine unchanged.36
Although excretion might be delayed in patients with impaired renal function, accumulation of unchanged drug is not expected to occur.1
Praziquantel, a pyrazinoisoquinoline derivative, is a synthetic heterocyclic anthelmintic agent.2, 3, 4, 5 The drug is structurally unrelated to other currently available anthelmintic agents.5
Praziquantel occurs as a white to nearly white, hygroscopic, crystalline powder with a bitter taste and is very slightly soluble in water and soluble in alcohol.1
Praziquantel tablets should be stored in tight containers80 at less than 30°C.1
Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.
Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.
Routes | Dosage Forms | Strengths | Brand Names | Manufacturer |
|---|---|---|---|---|
Oral | Tablets, film-coated | 600 mg |
1. Bayer. Biltricide® (praziquantel) tablets prescribing information. West Haven, CT; 2004 Aug.
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