I just started pregnyl and constituted the 5000iu cake with the solvent and used a 1cc slin pin to draw it all out. It went went pretty close to the 100 unit line marked on the syringe. So ya got to figiure it to be 500iu for every 10lines on the slin pin to amount to 5000iu total at the 100th line.
If you want 500 IU per pin then fill up 10 of them to the 10 IU line (on a terumo needle...I believe it was a terumo...they are at home, not here lol...)