Trematode (Fluke) Infections
Praziquantel is used for the treatment of schistosomiasis (bilharziasis) caused by all Schistosoma species pathogenic to humans. The drug has been used effectively for the treatment of individual patients and in mass-treatment and control programs.
Praziquantel is effective against all stages of Schistosoma infection including the acute phase and the chronic phase (which may be associated with hepatosplenic involvement). 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. Drug therapy may be initiated in patients with suspected neuroschistosomiasis pending the results of confirmative tests. 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. Mature schistosomes constantly produce eggs, most of which are retained in host tissues eliciting an immunologic granulomatous response and tissue injury and scarring. The severity of disease is related to the intensity of infection. Efficacy of antischistosomal drugs results from markedly reducing the worm load and thus preventing production of eggs.
Praziquantel has produced cure rates of 75-95% and/or egg reduction percentages of 80-98% in patients with schistosomiasis and is considered the drug of choice for the treatment of infections caused by S. haematobium, S. japonicum, S. mansoni, or S. mekongi; the drug is the only currently available anthelmintic shown to be effective in the treatment of infections caused by S. intercalatum or S. mekongi. Oxamniquine (no longer commercially available in the US) is considered an alternative to praziquantel in the treatment of infections caused by S. mansoni and may be effective in some areas in which praziquantel is less effective. Praziquantel has replaced niridazole or antimony salts (drugs not commercially available in the US) for the treatment of S. japonicum infections because of decreased toxicity and increased efficacy. The efficacy of praziquantel in the treatment of schistosomiasis may vary as a function of patient age and the degree of infection. Cure rates generally are lower in children and in patients with massive infections.
Travelers to endemic areas of the Caribbean, South America, Africa, Middle East, and Asia are at risk for schistosomiasis. 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. 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. 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.
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. 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. Serologic tests available from the CDC may be more sensitive and specific than commercially available tests, and may be particularly helpful for detecting light infections or before eggs appear in stool or urine. Following thorough clinical evaluation, seropositive individuals should receive praziquantel therapy. The possibility of neuroschistosomiasis should be suspected in any individual with CNS abnormalities who has returned from endemic areas. Such infections can occur several months after exposure to infested water, and eggs may be undetectable or difficult to identify in urine and stool. Presumptive praziquantel therapy should be initiated promptly whenever a strong suspicion of infection exists and should not be delayed pending confirmatory tests.
Clonorchiasis and Opisthorchiasis
Praziquantel is used for the treatment of clonorchiasis caused by Clonorchis sinensis (Chinese liver fluke) and opisthorchiasis caused by Opisthorchis viverrini (Southeast Asian liver fluke). Praziquantel has produced a cure rate of 86-98% in patients with clonorchiasis or opisthorchiasis and currently is considered the drug of choice for the treatment of these infections.
Other Trematode Infections
Praziquantel has been effective and is considered the drug of choice for the treatment of other trematode (fluke) infections, including those caused by Fasciolopsis buski (intestinal fluke),Heterophyes heterophyes (intestinal fluke),Metagonimus yokogawai (intestinal fluke),Metorchis conjunctus (North American liver fluke), Nanophyetus salmincola (formerly Troglotrema salmincola) (intestinal fluke), and Paragonimus westermani (lung fluke).
Praziquantel has been used in a limited number of patients for infections caused by Fasciola hepatica (sheep liver fluke), but the drug was inactive against the trematode in vitro in one study and treatment failures have been reported. 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.
Praziquantel also has been effective in a limited number of patients with infections caused by P. kellicotti (American lung fluke),P. heterotrema (lung fluke), and P. uterobilateralis (African lung fluke).
Cestode (Tapeworm) Infections
Praziquantel has been used for the treatment of cestodiasis (tapeworm infections) caused by certain cestodes pathogenic to humans, including Diphyllobothrium latum (fish tapeworm),Dipylidium caninum (dog and cat tapeworm),Taenia saginata (beef tapeworm), and T. solium (pork tapeworm). 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.
Praziquantel has been used for the treatment of infections caused by Hymenolepis nana (dwarf tapeworm) and is considered the drug of choice for these infections; nitazoxanide is recommended as an alternative.
Praziquantel is effective against the adult, juvenile, and larval stages of susceptible cestodes. 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.
Praziquantel has been used for the treatment of cysticercosis, including neurocysticercosis, caused by the larval form of T. solium (Cysticercus cellulosae).
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. However, use of antiparasitic therapy in patients with neurocysticercosis, especially those with seizures, has been controversial. Adverse nervous system effects (CSF reaction syndrome) occur frequently during praziquantel therapy for neurocysticercosis.
(See Cautions: Nervous System Effects.)Corticosteroids may be indicated; anticonvulsants (possibly long term) may be required.
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. In some patients, the risks of severe adverse effects associated with antiparasitic therapy may outweigh the potential benefits.
Praziquantel has been ineffective in patients with intraocular cysticercosis, 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. An ophthalmic examination should be performed to rule out intraocular cysts before use of praziquantel.
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. 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. Because praziquantel can kill Echinococcus (e.g., protoscoleces), the drug may be useful for perioperative prophylaxis or in case of spilling of cyst contents during surgery.