hi, I'm also on apidra and lantus the same as you. My endocrinologist told me that if I eat a snack and it is substantial to have 4 units of apidra with it. But it depends on my sugar levels, sometimes I will have some insulin and have more units than he said, other times I don't have any insulin. But yes, you can use the insulin for snacks, just less than you would with meals. I tend to mostly just have the 4 injections every day... but some days as mentioned I do need that extra insulin. I eat breakfast at 6 am so come 10 am I am hungry again.... plus it is tea break at work so I have something to eat to get me through to lunch as 6 hours without eating is too long for me.... the only time I ever do that is if I'm bedridden and really ill with vomiting.