Can I use miralax (polyethylene glycol) instead of golytely to prepare for my colonoscopy tomorrow?

Yes. Use large 255 gm bottle in 2 liters gatorade plus fleets enema plus 2 docolax pills.
Maybe. Miralax (polyethylene glycol) is similar to GoLytely except MiraLAX (polyethylene glycol) has no electrolytes like sodium, chlorid and potassium. It will clean you out well if taken as directed by your physician. But a word of caution: you can cause an electrolyte imbalance when using it as a prep for colonoscopy, which could impact your fluid and electrolytes , leading to cardiac invents during anesthesia. Daily use of a capful, no problem.