ELEVATED PLASMA LEVELS OF THEOPHYLLINE HAVE BEEN REPORTED WITH COMCOMITANT QUINOLONE USE. QUINOLONES INTERFERE WITH THE METABOLISM OF CAFFEIN. QUINOLONES INCLUDING NALIDIXIC, MAY ENHANCE THE EFFECTS OF THE ORAL ANTICOAGULANT WARFARIN OR ITS DERIVATIVES. NITROFURANTOIN INTERFERES WITH THE THERAPEUTIC ACTION OF NALIDIXIC ACID.SERIOUS G.I. TOXICITY IS SEEN WITH MELPHALAN AND NEPHROTOXICITY WITH CYCLOSPORINE. MINERAL SUPPLEMENTS, VITAMINS WITH IRON OR MINERALS, CALCIUM-, ALUMINUM-, MAGNESIUM-BASED ANTACIDS, SUCRALFATE OR DIDANOSINE, CHEWABLE/BUFFERED TABLETS OF THE PEDIATRIC POWDER FOR ORAL SOLUTION SHOULD NOT BE TAKEN WITHIN THE TWO-HOUR PERIOD BEFORE OR WITHIN THE TWO-HOUR PERIOD AFTER TAKING NALIDIXIC AID.CONCOMMITANT USE MAY LEAD TO REDUCED CLEARANCE OF CAFFEINE AND THE PROLONGATION OF ITS PLASMA HALF-LIFE.