Abstract: Objective   To observe the efficacy of oral administration of tribendimidine （TBD） at different dosages against Trichinella spirails encapsulated larvae in murine striated muscle.  Methods   A total of 88 BALB/c mice were divided equally into 11 groups. Each mouse was infected orally with 50 T.  spiralis encapsulated larvae. At day 29 after infection, TBD was each orally administered to mice of the 11 groups with doses of 0 （control group）, 50, 100, 150, 200, 250, 300, 350, 400, 450, and 500 mg/（kg·d）, respectively. All mice were administered once a day and lasted for 6 d, and untoward drug reactions for mice were observed. Mice were sacrificed at the 7th day after administration of TBD, the encapsulated larvae in diaphragmatic muscle, jugomaxillary muscle, pectoral muscle and gastrocnemius muscle were examined by pellet method, and the total, survival and dead worms were counted. The therapeutic effect was estimated on the basis of average quantity of encapsulated larvae per gram muscle.   Results   During the administration period, no untoward reaction were observed in mice of 50-300 mg/（kg·d） groups. Mice in 350 and 400 mg/（kg·d） groups showed body hair dishevelment, emaciation and food-intake decrease, death rates were 25% and 50%, respectively. All mice in 450 and 500 mg/（kg·d） groups died on day 4 and 5 after TBD administration, respectively. In control group, the highest total burden （per gram） was found in diaphragmatic muscle, followed by jugomaxillary muscle, gastrocnemius muscles and pectoral muscles. TBD at dose of 50 mg/（kg·d） was unable to kill encapsulated larvae. In the rest groups, with the increase of drug dose, the total worm burden and the number of survival worms showed a decreasing trend in four kinds of muscles, and were significantly lower than that of the control group （P＜0.05 or P＜0.01）. In 300 mg/（kg·d） group the number of survival worms in diaphragmatic muscle, jugomaxillary muscle, pectoral muscle and gastrocnemius muscle ［8.6±1.7, 2.8±0.7, 3.9±0.8, and 0， respectively］ were significantly lower than that of the control group ［3 648.1±989.2, 1 266.4±812.3, 701.9±196.4, and 711.6±334.6］ （P＜0.01）. All encapsulated larvae in the four kinds of muscle died in 350 and 400 mg/（kg·d） groups. With the increase of TBD dosage, the mortality of encapsulated larvae increased in the muscles, reached up to 98.6%-100% in 300 mg/（kg·d） group （P＜0.01）, and 100% in 350 and 400 mg/（kg·d） groups （P＜0.01）.   Conclusion   Oral tribendimidine administered at 50 mg/（kg·d） to mice for 6 d is unable to reduce worm burden in muscle. Tribendimidine 300 mg/（kg·d） effectively kill encapsulated larvae and is a suitable dose against encapsulated larva stage. However, tribendimidine at doses of 350 mg/（kg·d） and above for 6 d is toxic to mice and even causing death.

Key words: Tribendimidine, Trichinella spiralis, Encapsulated larvae, Therapeutic Efficacy, Mouse