Dear Ezel Bildik , it depends on the test you are doing and which organ you target. There are many methods including bio-informatic prediction tools which I highly advice you to try, else if I were you I would follow the approach below :
your in-vitro result is min dose, and you need to do cytotoxicity test in order to identify potential limit dose (max dose), then you can do trial between that limit dose and your IC50, in order to identify the in-vivo concentration that gives optimal results. I hope its useful,