Why take the risk?
To the best of my knowledge, there isn't any accurate info on how much of each is needed when mixing the 2 to be fatal, because it will be different depending on the individual.
For example, a long-time alcoholic can down couple pints of vodka w/o trouble, but for a nondrinker that would be bad, especially if a tranquilizer is involved. So, don't try it. Don't drink/drive. Be good. Good luck.