| Milbemycin oxime is one of a series of antibiotics produced through fermentation by Streptomyces hygroscopicus subspecies aureolacrimosus. The substance is a mixture of milbemycin A3 oxime and milbemycin A4 oxime at a 2:8 ratio. The objective of this study was to determine toxicological safety of milbemycin oxime by acute toxicity, Ames, micronucleus, sperm malformation and long-term toxicity tests. Kunming mice were chosen to study acute toxicity, micronucleus and sperm malformation, while chronic toxicity to Wistar rats. The results showed that the single use of milbemycin oxime did not effect the spontaneous movement, creep pole ability or express any synergy with continual in subthreshold dose. Milbemycin oxime had little toxicity to mice, and showed sex differences, the LD50 of milbemycin oxime to male and female mice were 1832 mg·kg-1 and 727 mg·kg-1, the 95% confidence intervals were 1637.57～2 022.08mg·kg-1 and 603.95～868.96mg·kg-1, respectively. In the Ames assay, four genotypic variants of the Salmonella strains (TA97, TA98, TA100 and TA102) carrying mutations in several genes were used. The average number of revertant colonies per plate treated with milbemycin oxime was less than double as compared to that of the negative control. In the micronucleus assay, the numbers of micro-nucleated PCE were counted, and the micronuclear rates were calculated. The obtained results indicated that milbemycin oxime could not induce the increase of micronuclear rates of PCE in bone marrow. In the sperm malformation test, the milbemycin oxime-treated groups showed no significant changes both in sperm abnormality and in a dose-dependent manner. In one month after administration, there were no significant changes in the appearance and movement of rats, except some rats show low spirit, but recovered when the administration stopped; and the hematology parameters were all in the normal scales; blood biochemical indicators and uronoscopy were normal before and after administration; in the high dose group there were some pathological changes in lung, liver, intestine and spleen, while others were normal.For the convenience of clinical application, the study on the pharmacodynamics of milbemycin oxime in vitro against Toxocara canis was carried out. In vitro action of milbemycin oxime against isolated adult Toxocara canis from dog intestine was observed after exposing 4, 8, 12, 24h at the concentration of 10-4, 10-5, 10-6, 10-7, 10-8 g·mL-1, the results showed that the concentrations of 10-4, 10-5, 10-6g·mL-1 were 100% efficiency to worms, while those of 10-7, 10-8 g·mL-1 were 66%, indicating that the concentration played important role on it. The above concentrations were used to study the effect of milbemycin oxime to Toxocara canis eggs, with the more dose increasing and prolonging of incubation time, the eggs need longer development time, and the number of stageⅤeggs were less; at the same time, the eggs that incubated 28d after acting with drug were used to infect mice, the results showed that milbemycin oxime could obviously decrease the infectivity of eggs. After being coacted with different concentrations (10-5,10-6,10-7 g·mL-1) of milbemycin oxime, infective Toxocara canis eggs (about 1,000 eggs) that were developed from fertilized eggs were orally infected on mice. Over 3 and 5 days of post-inoculation (p.i.), mice were killed by cervical dislocation, respectively. The lungs were removed to record the macroscopic and histopathological injury. After 3 and 5 days of p.i., the lung of mice inoculated by infective Toxocara canis eggs with low concentration of milbecycin oxime (10-7 g·mL-1) for 12h showed obvious macroscopic lesions, while no lesions were found at high concentration of milbecycin oxime (10-5, 10-6 g·mL-1). It indicated that milbemycin oxime could make the infective Toxocara canis eggs lose the infection. |
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