If someone does reach the max amount of one particular type of enzyme and still shows evidence of malabsorption, they can change what type of enzyme they give him; different brands vary in their composition. They can also try adding an antacid, since those can also help the enzymes work more effectively.
It's very, VERY unlikely that he's reached the 'end' of what can be done for him digestively speaking... I wouldn't worry yet, esp if this is the first enzyme he has been on. And yes, it does take a very large amount of enzymes to truly 'overdose' on them. That said, most drs/nutritionists do try to work within a 'formula' of a certain amount. Who knows how they come up with their amount though, since you'd see how widely it varies if you did a 'poll' here on enzyme dosing!
Keep in mind as well that he's at an age where his diet will be undergoing a lot of changes in upcoming months: adding more solids, gradually decreasing formula or breastmilk, stools often change with the introductions of new foods... you'll have the added 'fun' of determining appropriate enzyme amounts for solid-food meals as well. So it's tricky... you'll always want to keep in the back of your mind any other possible reasons for stool issues other than the obvious cf-related ones.
I wish the best and hope this resolves soon for Sam! Adding a solid w/ natural enzyme properties does seem like a good idea, btw, if he likes it. <img src="i/expressions/face-icon-small-smile.gif" border="0">
eta> Emily's consumption at one sitting varies widely, since what she has varies so much, unlike a baby who has the same thing nearly every time. We have guidelines for what to give her for various snacks and meals and a daily max. I *think* her weight figures into the quick math I've seen her dr. do in figuring it out. She weighs in the high 40's most of the time and her max is 20 Creon 12's a day. She also takes Prevacid twice a day.