Pyrantel resistance

Figure 21.11A illustrates representative vesicle-attached recordings from a sensitive isolate (SENS), a pyrantel-resistant isolate (PYRR) and a levamisole-resistant isolate (LEVR) produced by 30 pM levamisole. There are differences in mean P-open values of receptors between sensitive and resistant isolates that would produce, on average, a reduction in the effect of the anthelmintic. However, one of the puzzling, but very consistent, observations is that there is a big range in the P-open values observed in different patches under the same experimental conditions in the same isolate (Fig. 21.1 IB). For example, the P-open values of the sensitive isolate were observed to vary between 0.090 and 0.003 at -50 mV with 30 pM levamisole, a 30-fold difference between the biggest and the smallest P-open...

Bjorn H. Hennessy DR, Friis C. The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs. International Journal for Parasitology, 1996, 26 1375-1380. 

Varady, M., Bjorn, H., Craven, J. and Nansen, P. (1997) In vitro characterization of lines of Oesophagostomum dentatum selected or not selected for resistance to pyrantel, levamisole and ivermectin. International Journal for Parasitology 27, 77-81. 

Pyrantel is quickly metabolized in the body, a small proportion remaining intact by the time it is excreted. Individual metabolites of pyrantel have not been yet identified. Nevertheless, it is known that at least half of them contain the N-methyl-l,3-propanediamine structure of the tetrahydropyrimidyl ring, which is more resistant to the metabolic attack than the thiophene ring (6). 

Sangster N C 1999 Pharmacology of anthelmintic resistance in cyathostomes will it occur with the avermectin millbemycins. Veterinary Parasitology 85 189-204 Tarigo-Martinie J L, Wyatt A R, Kaplan R M 2001 Prevalence and clinical implications of anthelmintic resistance In cyathostomes in horses. Journal of the American Veterinary Medical Association 218 1957-1960 Taylor S M, Kenny J 1995 Comparison of moxidectin with ivermectin and pyrantel embonate for reduction of faecal egg count in horses. Veterinary Record 137 516-518 Uhlinger C 1990 Effects of three anthelmintic schedules on the incidence of coiic in horses. Equine Veterinary Journal 22 251-254... 

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