May lead to pathological increases of serum Ca level or intensification w/ medicaments containing Ca (eg, acetolyte). Reduce possible administration of Al hydroxide as uremic 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/cardiac-active glycosides & hence, increased risk of arrhythmia w/ raised blood Ca conc.