We were also on avodart from a couple weeks after biopsy until surgery.
Yes, you have to multiply your PSA. Our doc says by 1.5 after three months, and 2.0 after six months. (I don't think they have this down to an exact science yet, but these are the best they have after the research they have done).
For instance our's went from 3.7 before biopsy that showed cancer, down to 2.4 on avodart, doc multiplied it by 1.6 (was a little bit past three months for us) for a pre-surgery PSA of 3.8.
With your PSA going up on Avodart, I would get another biopsy, imo (not sure if you just got another one when you say "same diagonsis?".) Ask for a second opinion. oh, and i would also ask for the free psa as mentioned above with next blood test. (maybe do it before the next biopsy, so you have that without having to wait for 8 weeks after a biopsy).
PSA: 3.7 (2005: 3.4, 2004: 4.0)
Biopsy: 1/10 cancerous, 5% of one core, right apex.
Da Vinci: April 10, 2007
Path results: 1% of prostate involved. Very small tumors on both right and left apex. Negative margins, negative seminal vessicles, lymph nodes left intact. Gleason upgraded 3+4=7.
1st PSA Results: May 11, 2007 <.01