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Since the introduction of the first antischistosomicide, tartar emetic, many compounds have been tested with the aim to develop the ideal antischistosomicidal drug with the following qualities:
1) Absence of side effects and toxicity in man, 2) High activity against the three major species of schistosomes parasitic in man, 3) Effective after a single or a one day-treatment preferably after oral administration, 4) Active against all stages of schistosomes in man. These lead to a new heterocyclic pyrazino isoquinoline with high anti-parasitic efficacy, praziquantel.
Praziquantel is a newly developed anthelminthic drug with excellent activity against all schistosome species parasitic in man. A further progress is the fact that the efficacy of this drug is not significantly influenced by inter-strain variation of schistosomes in contrast e.g. to hycanthone and oxamniquine, and it is effective against all stages of the immature infection.
It has also been effective against Clonorchis sinensis (Chinese liver fluke), Metagonimus yokogawai (intestinal fluke), and adult larval stages of important human tapeworms, including Hymenolepis nana and cysticercosis.Praziquantel acts by increasing the permeability of the worm's cell membrane to calcium ions, causing massive contraction and paralysis of its musculature, followed by disintegration of its tegumental layer. A rapid absorption, distribution and elimination after oral application in man were observed. No major toxic reactions have yet been found with praziquantel. Transient abdominal pain can occur, especially when the drug is given as a single oral dose. Praziquantel has not been found to be mutagenic in a variety of assays. Chronic toxicity tests in small animals so far offered no indication of carcinogenic potential.
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