Well, since the bioavailability of oxymorphone is 40% when insufflated, when you snort 10mg, only about 4mg actually make it to your bloodstream. So technically that should equate to 80mg of oxycodone (50% was an approximation, my mistake it makes a big difference actually).
So saying that 4mg of Opana in the blood = 80mg of oxycodone in the blood is an exact. Once in the blood this is how they compare in strength.
However, the amounts consumed don't always equate exactly to the approximated bioavailability. In other words, when you snort 10mg of Opana it doesn't mean that exactly 4mg of oxymorphone made it into your system. It varies vastly from person to person and even each time you consume it.
This is partly because everybody responds differently to different chemicals and partly based on how well you snorted/consumed it.
When you say you insufflate Opana, do you mean Opana ER or IR? If you ingested the ER formulation it is very hard to judge how well your body absorbed the oxymorphone. This is because of the stupid gel timerx formulation of the pills. Not only does it clog up the nose, but a lot of the oxymorph is still delivered in a time release fashion, even though you crushed it up.
In the timerx system, the oxymorphone is basically trapped inside of these "beads" of pill binder. When they come in contact with water, they release the oxymorphone and absorb water, basically trading it off. This is why when you crush it up and swallow it, a lot of it is still time released. They did a really good job on the anti-abuse front. Even when you break the pill down these smaller "beads" still deliver the drug with the same system.
So the same thing happens in your nose. The oxymorphone has to come in contact with water and be released. And taking into account how it gels up inside the nose, depending on how much it gets clogged, the bioavailability could go down to 30% or even 20%.
So while it can't be known for sure, 40mg of oxycodone might feel the same as 10mg of Opana to you because it is being partially time released and you are feeling it less intensely over a longer period of time.
Also, you have to remember that although they compare in strength a certain way, they are different drugs and give a different type of euphoria. Even though they compare in analgesic properties and CNS depression, it could take that much Opana to give you the same "feeling" as 40mg of oxycodone.
