Dr.Brown's actually made Sergio worse. We used them for the first three months and he was constantly passing gas. I bought some Avent bottles from a mom-to-mom group I belong to on FB, just because we only had 4 Dr.B bottles and I was sick of constantly washing them. Well, wa-la! He hardly passes gas anymore...only when he's pooping really.
We used to give him room temp bottles and moved to warm at the same time we switched to Avent, so I'm not sure if that helped since I did both at the same time. If I'm out and he's hungry, I just set the bottle on top of the heating vent on my car for a few minutes with the heat on high and it warms it right up. Sergio does the same thing throughout his bottles; swats it away and then cries. I think he's ready for the next nip size.