There's an excellent article on isoniazid hepatoxicity on e-medicine:
http://emedicine.medscape.com/article/180554-overview
Wayti2000, the medication your son was on can unfortunately cause hepatitis which can lead to the changes in the liver enzymes you're mentioning. I know you're supposed to wait to see if there are changes to the enzymes after a week's time, but you may want to call your son's doctor to see if you can get some further testing done, or have him seen to be evaluated.
The elevations may not be due to the medication, but the levels you're mentioning are too darned high to overlook.