Hi Sushil,

We usually go for a therapeutic dose of 1/40 or 1/50 of the LD50.

Best

Thank you sir, i also did the same. As one reviewer askes me this question. So want to cross check. Could you provide me some references for it?

use the does that shows the highest effectiveness for further studies

I think the LD50 value for your plant is too high. Acute toxicity studies should have been done. You should consider administering 2000 mg/kg p.o. and if no mortality is observed, then select a 1/10th, 1/20th and 1/40th dose for your experiments. This will also be in accordance with the OECD guidelines. 

Dear Dr. Ashok but there was no mortality found on 2g/BW . 

I agree with Alok, you should firm perform acute toxicity studies. The LD50 value for your plant appears to be too high. First you should consider administering high doses and then based on results you can choose further doses of the bioassay accordingly  Specified OECD guidelines should be followed.