page has a collection of Peruvian slang words.
They have an interesting meaning for "blanca" and while there's no "pula", there's "pucha", which sounds close enough, especially in accented, soft-consonant Spanish.
So, from this we can deduce that Barranca has just snorted a bad line, and now he's cursing it, "pucha blanca"... as in, "this friggin' coke".
No need to thank me. I'm here to help.