Празиквантел

Описание

Praziquantel (PZQ) is an isoquinoline derivative with most of the biological activity found in the levo enantiomer. The compound has no activity against nematodes, but it is highly effective against cestodes and trematodes.

Химические свойства

White Solid

Использование

Praziquantel is a potent anthelmintic used against schistosome and many cestode infestations. It is used to study voltage-gated Ca2+ channels and is a potential small molecule neurogenic.

Показания

The neuromuscular effects of praziquantel (Biltricide) appear to increase parasite motility leading to spastic paralysis. The drug increases calcium permeability through parasite-specific ion channels, so that the tegmental and muscle cells of the parasite accumulate calcium.This action is followed by vacuolization and the exposure of hitherto masked tegmental antigens, lipidanchored protein, and actin. Insertion of the drug into the fluke’s lipid bilayer causes conformational changes, rendering the fluke susceptible to antibody- and complement-mediated assault.

Приобретенная устойчивость

There is evidence that resistance to praziquantel is emerging in schistosomes, although there is debate as to whether treatment failures are due to resistance or innate tolerance.

Фармацевтические приложения

A synthetic pyrazinoquinoline formulated for oral administration. It is stable in the dry state, but hygroscopic.

Механизм действия

Praziquantel is readily absorbed (80% in 24 hours) after oral administration, with serum concentrations being maximal in 1 to 3 hours; the drug has a half-life of 0.8 to 1.5 hours. Its bioavailability is reduced by phenytoin or carbamazepine and increased by cimetidine. Dexamethasone decreases plasma praziquantel levels by 50%. Praziquantel is excreted by the kidneys.

Фармакокине?тика

Oral absorption: >80%
C_max 50 mg/kg oral: 1 mg/L after 1–2 h
Plasma half-life: parent drug: 1–1.5 h
metabolites: 4–6h
Plasma protein binding: 80%
Praziquantel is rapidly absorbed when given orally, but it undergoes extensive first-pass biotransformation and the concentration of unchanged drug in plasma is low. The major metabolite, a 4-hydroxy derivative, retains little to no antiparasitic activity. About 80% of the oral dose, as parent drug and its metabolites, is excreted in the urine by the fourth day post-treatment, 90% of this in 24 h. A higher peak plasma concentration is achieved in infected people, but other pharmacokinetic values are unchanged.

Клиническое использование

2-(Cyclohexylcarbonyl)-1,2,3,6,7, 11b-hexahydro-4Hpyrazino[2,1-a]isoquinolin-4-one (Biltricide) is a broadspectrumagent that is effective against various trematodes (flukes). It has become the agent of choice for the treatmentof infections caused by schistosomes (blood flukes).
The drug also provides effective treatment for fasciolopsiasis(intestinal fluke), clonorchiasis (Chinese liver fluke),fascioliasis (sheep liver fluke), opisthorchosis (liver fluke),and paragonimiasis (lung fluke). Praziquantel increases cellmembrane permeability of susceptible worms, resulting inthe loss of extracellular calcium. Massive contractions andultimate paralysis of the fluke musculature occurs, followedby phagocytosis of the parasite.
Following oral administration, about 80% of the doseis absorbed. Maximal plasma concentrations are achievedin 1 to 3 hours. The drug is rapidly metabolized in theliver in the first-pass. It is likely that some of the metabolitesare also active. Praziquantel occurs as a white crystallinesolid that is insoluble in water. It is available as600-mg film-coated tablets. The drug is generally welltolerated.

Побочные эффекты

Very few side effects have been reported. In the treatment of cerebral cysticercosis the death of cysts in the brain may cause local inflammation and edema, but this usually subsides quickly. Ocular cysticercosis should not be treated with this drug, because parasite destruction in the eye can lead to irreparable lesions. Adverse events seen in the treatment of schistosomiasis, including abdominal pain, nausea, anorexia, diarrhea and mild neurological effects, are almost certainly due to the death and disintegration of the large adult worms.

Профиль безопасности

Poison by intraperitoneal route.Moderately toxic by ingestion and other routes. Humanmutation data reported. When heated to decomposition itemits toxic fumes of NOx.

Метаболизм

Praziquantel is rapidly absorbed and undergoes hepatic first-pass metabolism. The metabolites are either less active or inactive and consist of hydroxylated compounds. In the serum, the major metabolite appears to be the monohydroxylated 4-hydroxycyclohexylcarboxylate, whereas in the urine, 50 to 60% of the initial PZQ exists as dihydroxylated products.These hydroxylation reactions are catalyzed by CYP2B6 and CYP3A4. The metabolites would be expected to exist in the conjugated form in the urine.