Hi, taking a Gliptin is probably because of your high levels, or insulin resistance and because of insulin resistance, you could have a weak initial insulin response.
The Gliptin will produce insulin, so that you can have enough insulin to cater for the amount of glucose derived from your food.
I too have had liver function problems. The secret is to drink plenty of water before y your blood panel tests. This will flush out the liver and your function results should improve.
I have been on sitagliptin for nearly eight years and had no side effects.