bioavailability, type of minerals

What is the bioavailability of this vitamin? Where in the digestive tract is this vitamin absorbed and how quickly is it available to the body to be utilized?

I am receiving this vitamin via mail order pharmacy and I spoke with the pharmacist and asked him about the minerals. It wasn't on the label, and I'd really like to know, what form of Calcium is used, carbonate, citrate, etc., and what is the form of Magnesium? How is this prescription vitamin better than those at the grocery or healthfood store? I have read about large volumes of undisolved vitamins being found in the porta-johns, and the name of the vitamin was still ledgeable. I am concerned about my body eliminating expensive vitamins and minerals and not being absorbed. It is important to me to trust what I put in my body will be for my benefit and support/improve my health.

Thank you in advance for answering my questions and concerns. I really want to be an informed consumer and a partner in my own healthcare.

Sincerely,

Jo