May trigger or worsen pathological increase in serum Ca level w/ medicinal products containing Ca eg, acetolyte. Reduce dose of Al hydroxide as uremic symptoms improve w/ therapy. Concomitant use w/ medicinal products which form poorly soluble compd w/ Ca eg, tetracyclines, quinolones (eg, ciprofloxacin & norfloxacin), prep containing Fe, fluoride & estramustine. Increased sensitivity to medicinal products which increase heart action (eg, cardiac glycosides) & thus risk of cardiac arrhythmia is increased if administration of treatment leads to increased blood levels of Ca.