吡喹酮

吡喹酮（Praziquantel，或Biltricide）為一種用於人類及動物的驅蟲藥，專門治療絛蟲及吸蟲。對於血吸蟲、中華肝吸蟲、廣節裂頭絛蟲特別有效，吡喹酮為世界衛生組織基本藥物標準清單上的藥物，為世界上對於基本公共衛生最重要的藥物之一。1970年代由拜耳公司的藥學部研發成功。

**醫療用途**
吡喹酮可以用於治療人類、哺乳類，以及魚類的寄生蟲病。包含腸胃道或是外部的感染，以下為其適用疾病：- 包蟲症：為包囊蟲幼蟲所引起的感染症。- 豬囊尾蚴病：為豬肉絛蟲幼蟲感染腦部或肌肉所引起的疾病（但在腦囊蟲病則以阿苯達唑效果較佳）- Feline taeniasis caused in cats by gastrointestinal infection with adult tapeworms of the species Taenia taeniaeformis; used either alone or in combination with pyrantel pamoate- Toxocariasis in cats and dogs whose gut is infected with the roundworms/nematodes Toxocara cati or Toxocara canis, respectively; use is often combined with pyrantel 
*Schistosomiasis caused by trematodes of the genus Schistosoma.As of 2005, praziquantel is the primary treatment for human schistosomiasis, for which it is usually effective in a single dose.
*Clonorchiasis brought on by the Chinese liver fluke Clonorchis sinensis
*Paragonimiasis caused by infection with lung flukes, mostly of the species Paragonimus westermanitime=March 2012
*Fasciolopsiasis caused by intestinal fluke Fasciolopsis buski
*Diplozoon paradoxum and other Trematoda infections of many fish species

**副作用**
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 pre-existing 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 colic. 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 cell counts
*Other locations/body as a whole: Lower back pain, myalgia, arthralgia, fever, sweating, various cardiac arrhythmias, and hypotension

**Drug interactions**
The antibiotic rifampicin decreases plasma concentrations of praziquantel.
Carbamazepine and phenytoin are reported to reduce the bioavailability of praziquantel.
Chloroquine reduces the bioavailability of praziquantel.
The drug cimetidine heightens praziquantel bioavailability.

**Mechanism of action**
The mode of action is not exactly known at present, but experimental evidence indicates praziquantel increases the permeability of the membranes of schistosome cells towards 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 including focal disintegrations and disturbances of oviposition (laying of eggs) are seen in other types of sensitive parasites.
Another hypothesis concerning 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 such as adenosine de novo.
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."
Praziquantel is administered as a racemate, but only the (R)-enantiomer is biologically active; the enantiomers may be separated using a resolution of an amine obtained from praziquantel.

**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 classes B ll///d C), the serum half-life is increased to 3 to 8 hours. Praziquantel and its metabolites are mainly excreted renally; within 24 hours 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 (Elberfeld and Darmstadt) in the mid 1970s. 

**商品名**
Biltricide (Bayer) 600 mg Tablets：人類使用
*Cesol (Merck) Tablets
*Cestoved (Vedco) ：藥片或注射劑，獸醫使用
*Cysticide (Merck) Tablets
*Distocide (Shin Poong Pharm. Co. Ltd) 600mg tablet：人類使用
*Distoside (Chandra Bhagat Pharma Pvt Ltd) 600mg tablet：人類使用
*Droncit (Bayer) ：獸醫使用
*Drontal (combination with pyrantel pamoate) (Bayer)：獸醫使用
*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
*Kaicide (Taiwan)
*Milbemax (combination with milbemycin oxime) (Novartis)：獸醫使用
*Popantel (Jurox)
*PraziPro (Hikari) ：水生動物飼養使用
*Praz-Tastic (NFP/National Fish Pharmaceuticals) ：水生動物飼養使用
*Pure Prazi (COTS Koi/Children of the Sun Koi)：水生動物飼養使用
*PraziPure (J.K.O., Inc. d/b/a Kodama Koi Farm & Kodama Koi Garden; licensed by COTS Koi)：水生動物飼養使用
*Profender (combination with emodepside) (Bayer) ：獸醫使用
*Tape Worm Tabs (Trade Winds) ：獸醫使用
*Zentozide (Berich (Thailand) Co)

**核准狀況**
吡喹酮名列世界衛生組織基本藥物標準清單之中，是世界上對於基本公共衛生最重要的藥物之一。
在英國，吡喹酮並未獲准在人體上使用。但在必要時可以根據在患者實名的情況下進口。在英國吡喹酮可以作為獸用驅蟲藥銷售。
在美國，吡喹酮被FDA批准用於血吸蟲病及肝吸蟲病的治療，儘管它對其他種類的感染也有效。

**參考文獻 ==