In theory, they should be about the same, dextropropoxyphene (Darvocet) is basically a synthethic version of
codeine, it tricks the brain to thinking the body has consumed codeine and produces the same effects.
However, we all know that theres nothing better than the real thing. Codeine is stronger and a more effective pain killer for knee pains, but more addictive and increases withdrawel symptoms.
If your asking if it's water soluble because you want to shoot it up, the answer is no, im sure it would clog the needle. Very dangerous also.