ED₅₀ Ditermination And Toxicity Study On Long-term Intravenous Administration Of Emulsified Isoflurane In Dogs

The long-term toxicity studies of inhaled isoflurane were begun in 1970s.Massive experiments in animals and clinical uses showed that it was safe.Recently,our study group established a method of preparing emulsified isoflurane 8%（vol/vol）by using 30%Intralipid（?）.Its quality including particle size,stability,and asepsis state are measured up to the requirements of State Food and Drug Administration.Our previous studies showed that intravenous injection of 8%EI had a greatly shortened onset time and a much shorter recover time compared with propofol.To the best of our knowledge,there has been little work focusing on determination of its ED₅₀ and the long-term toxicity for i.v.injection in dogs.In these two studies,we aim to measure the ED₅₀ for single bolus in dogs and to estimate whether emulsified isoflurane will induce any impairment in dogs’ organs or systems and estimate whether the impairments are reversible as well.Part one Determination of median effective dose of intravenous emulsified isoflurane in dogsObjective To measure the median effective dose(ED₅₀)of emulsified isoflurane（8%EI,vol/vol）for intravenous injection in dogs and estimate whether 8%EI induces impairments of dogs’ organs or systems and whether the impairments are reversible.Methods 8%EI which diluted into the same volume（2.0ml·kg-1）was injected to 24 mongrel dogs（12male,12female）with a single bolus via the right cephalic vein approach at the same rate（0.5ml·kg-1 10secs-1）,and the median effective dose was measured by the up-and-down method.The loss of forepaw righting reflex（FRR）was considered as successful anesthesia induction.Loss and return time of FRR and stand time were recorded.At each timepoint of 1min,1.5min,2mim,3min,4min and 5min after the single bolus,values of HR,MAP,and SPO2 were recorded,respectively.All dogs were fed for further two weeks and general conditions such as physical activity,hair color,respiratory tract infections,local reaction at the injection site and characteristics of the stools were daily observed.Results ED₅₀ of 8%EI for i.v.injection in dogs was（122.4±26.8）mg·kg-1.Loss and return time of FRR and stand time were（62.5±9.2sec）,（110.8±57.3sec）,（255.1±70.8sec）,respectively.Values of MAP at lmin timepoint after the injection were less than that of the baseline（P<0.01）.Compared with the baseline values,the difference of HR at 1.5min timepoint after the injection was significant（P<0.01）.Meanwhile SPO2 values were lower than the basic（P<0.05）.However,all SPO2 values were above 94%and no death happened in all dogs.Conclusion This study showed that 8%EI could be safely injected in dogs and it was effective in producing rapid onset and predicable general anesthesia.Part two Toxicity study on long-term intravenous administration of emulsified isoflurane in beagle dogs Objective To estimate whether emulsified isoflurane induces impairments of dog s organs or systems and whether the impairments are reversible for thirty consecutive days’ intravenous administration of emulsified isoflurane.Methods 24 Beagle dogs were divided at random into the following four groups（3male and 3female for each group）:control group one with saline solution 2.0ml·kg-1 daily;control group two with 30%fat emulsion 2.0ml·kg-1 daily;study group A with emulsified isoflurane 1.13ml kg-1 daily;study group B with emulsified isoflurane 1.13ml·kg-1 every two other days.All dogs were given corresponding drugs which diluted into the same volume（2.0ml·kg-1）with 30%fat emulsion via tail vein approach at the same rate（1.7ml·kg-1·min-1）.At the end of twenty-four hours after the last injection,blood samples of all dogs were collected for the determination of hematology and biochemistry values and cell counts of bone marrow were also determined,and half dogs of each group were killed and tissue specimens were collected for histopathologic investigation.The other dogs were observed for two weeks and disposed previously.Results 1.Hematology values:prothrombin time（PT）values of emulsified isoflurane group A and B were lower than that of control group two at the end of two weeks after the last injection（P<0.05）,but compared with that of control group one,the difference was not significant（P>0.05）.2.Biochemistry values:the difference of serum urea values between group A and control group two was significant at the end of twenty-four hours after the last injection（P<0.05）,but compared with control group one,it was not significant（P>0.05）.3.Electrocardiogram values:Q-T interval of emulsified isoflurane group A was longer than that of two control groups at the end of twenty-four hours after the last injection（P<0.05）.However,the difference was not statistically significant when it was compared with that determined in observation period.4.Histopathologic investigation showed that no specific lesions were found in any organ or tissue in all dogs.Conclusion Long-term intravenous administration of emulsified isoflurane did not impair dog’s organs and systems.