Calcium supplements should be taken separately from any medications (prescription or non-prescription).
Why?

Numerous antibiotics, bile acid sequesterants, certain chemotherapy drugs, corticosteroids, NSAIDs, and thyroid hormone may interfere with or impair the absorption of calcium. They may also increase calcium excretion.

On the other hand, calcium supplements may decrease the absorption and bioavailability of tetracycline, thereby reducing the effectiveness of this drug.

From: "Calcium Plus Vitamin D". HART Toolkit, 2001.