20610 & Depo-medrol injection

When Dr. performs CPT® 20610 he uses Depo-medrol.
We have never billed for the Depo-medrol 40 mg/ml.
1)Which CPT® should I use additionally to the 20160 for this Depo-medrol?
2)Any modifier?
3)Do I need to bill the same amount we paid for the med?
Please help!!!! It's great to hear from all of you.