My Little cousin mixed alcohol with Lexapro?

Well before anything i would like to wish a happy new year to everyone, now lemme explain the situation, well since it was new years eve my 15 year old cousin thought he could drink a small amount of liquor without no one noticing, he drunk about 4 shots of triple cream liqueur, but the problem is that he also takes Lexapro in the morning, Now 4 shots is a small amount especially since it was with the bottle cap, but he seems to be complaining of heartburn and nausea, the alcohol percentage is 17%. What could be the cause of this and is this dangerous?? We also gave him Pepto Bismol, will that do him any good??