As well documented in scientific literature, fenbendazole (FBZL) has been evaluated for the treatment of gastrointestinal nematodosis in animals (Stewart et al., 1981). Despite poor absorption from the gastrointestinal tract, oral administration of FBZL has resulted in clinical efficacy in the treatment of ascaridosis in pigs, which is most probably due to an induced local effect. The objective of this study was to measure the effect on the maintenance of concentrations in the gastrointestinal tract after treatment and to assess the clinical effect of Pigfen® 40 mg/g premix used in pigs naturally infected with Ascaris suum.
Materials and methods
Six groups of six pigs (Danube White), of both sexes (28.0 - 31.5 kg), at about 12 weeks of age, were used. All pigs were naturally infected with A. suum. On day 0 of the trial, the infected groups (II-VI) were treated in feed with a single oral dose of 5 mg/kg bodyweight (BW) FBZL as Pigfen® 40 mg/g premix. The concentration of FBZL was assessed applying HPLC determination in plasma and small intestinal contents of pigs. Faecal samples were collected and nematode egg counts were determined using a McMaster technique. Efficacy of the medication was evaluated after euthanasia and necropsy of all pigs and the count of adult forms of A. suum was determined in the small intestines. The results of the examination were determined according to t-test of Student-Fisher (mean ± SEM).
The concentrations of FBZL in the plasma and in the small intestinal contents 12 hours after treatment were 0.471±0.04 μg/mL and 2.5±0.12 μg/g, respectively (Table 1). Twenty four and 36 hours after treatment, FBZL concentrations in the plasma were lower as compared to those found 12 hours after treatment. Concentrations of FBZL were found in the small intestines contents from 12 hours to 72 hours after treatment, the higher concentration of 106.4±4.82 μg/g being found 24 hours after treatment.
No statistically significant difference was found in the A. suum egg counts in the faecal samples of the pigs of all groups before treatment (Table 2). When included in the feed of infected pigs (II-VI) at a dose of 5 mg/kg BW, FBZL led to statistically significant decrease in the A. suum worm counts in the small intestines. Worm Count Reduction was 44.97% 12 hours and 100% from 24 hours to 72 hours after treatment.
Conclusions and Discussion
The study results show that in-feed administration of FBZL at 5 mg/kg BW has significant therapeutic effects in pigs naturally infected with A. suum. FBZL concentrates in the small intestines and has a high intestines/plasma ratio, which has a significant role in establishing PK/PD relationships and clinical efficacy against ascaridosis in pigs (Mottier et al., 2006; Zhao et al., 2017). The present study highlights the maintenance of FBZL concentrations in the intestines and the impact of this reservoir on the evolution of FBZL, which has been demonstrated by statistically significant FBZL concentrations found in the small intestines up to 24 hours after treatment as compared to those found after 12, 36 and 48 hours. The 100% efficacy of FBZL against A. suum has also been confirmed in this study (Baeder et al. 1974).
The results obtained indicate that the maintained concentrations of FBZL can help in the designing of efficient medication strategies in sustainable pig farming, especially to treat and overcome ascaridosis.
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Zhao, J., Williams, A.R., Alstrup-Hansen, T.V., Thamsborg, S.M., Cai, J., Song, S., Chen, G., Kang, M., Zhang, Z., Liu, Q. and Han, Q. (2017). An in vitro larval migration assay for assessing anthelmintic activity of different drug classes against Ascaris suum. Veterinary Parasitology 238. 43-48.