Ca-containing drugs may cause or aggravate elevated serum Ca levels. Avoid drugs that form hardly soluble compd w/ Ca eg, tetracyclines, quinolones (eg, ciprofloxacin & norfloxacin as well as drugs containing Fe, fluoride or estramustine). An interval of at least 2 hr should elapse between intake of other drugs. Cardioactive glycosides; Al hydroxide. Monitor for decreased serum phosphates levels.