For the love of all that is holy, DO NOT take Naloxone/Naltraxone while having opiates in your system! Imagine day three / four of a heroin withdrawal, the peak if you will, coming on in about 5 minutes, and I mean FULL ON. It was the most terrifying experience of my life.
I, like you, thought "yeah, I'll just do some Nalaxone and be clean, job done". Oh no...within 2 minutes I had a back ache and felt sick, and got that horribly panicky feeling that I'd made a BIG mistake. I stuck my fingers down my throat but it had dissolved instantly. Then I started throwing up properly, withdrawal stylee, and having back and leg spasm's that literally threw me off the sofa. Within a max of ten minutes, probably more like 6 or 8 (and this is from a tablet of Naltraxone remember, not anything IV!) I was in full on withdrawal; weak, couldn't stand, being sick, spasm's, the full works. At this point I very very nearly called an ambulance but a friend crushed up about 8mg Xanax that I manages to not throw up and ride it out for the next 6-8 hours.
Trust me on this one, BAD IDEA.