May lead to pathological increases of serum Ca level or intensification w/ simultaneous administration of medicaments containing Ca (eg, acetolyte). Reduce possible administration of Al hydroxide due to improved uraemic symptoms under therapy. Reduction of serum phosphate might interfere w/ the absorption. Not to be taken w/ drugs that form sparingly soluble compd w/ Ca (eg, tetracyclines, ciprofloxacin & norfloxacin, Fe fluoride & estramustine-containing drugs). Increased susceptibility towards heart/cardiac-active glycosides & hence risk of arrhythmia w/ the raise of blood Ca conc.