May lead to pathological increase of serum Ca level or intensification w/ medicaments containing Ca (eg, acetolyte). Reduce possible administration of Al hydroxide as uraemic symptoms improve. Reduction of serum phosphate. Interfered absorption w/ drugs that form sparingly soluble compd w/ Ca (eg, tetracyclines, quinolones (eg, ciprofloxacin, norfloxacin), Fe, fluoride, & estramustin-containing drugs). Susceptibility towards heart/cardio-active glycosides & hence, risk of arrhythmia increases w/ the rise of blood Ca conc.