Colestipolinteractions

Since colestipol hydrochloride is an anion exchange resin, it may have a strong affinity for anions other than the bile acids. In vitro studies have indicated that colestipol hydrochloride binds a number of drugs. Therefore, colestipol hydrochloride tablets may delay or reduce the absorption of concomitant oral medication. The interval between the administration of colestipol hydrochloride tablets and any other medication should be as long as possible. Patients should take other drugs at least one hour before or four hours after colestipol hydrochloride tablets to avoid impeding their absorption. Repeated doses of colestipol hydrochloride given prior to a single dose of propranolol in human trials have been reported to decrease propranolol absorption. However, in a follow-up study in normal subjects, single-dose administration of colestipol hydrochloride and propranolol and twice-a-day administration for 5 days of both agents did not affect the extent of propranolol absorption, but had a small yet statistically significant effect on its rate of absorption; the time to reach maximum concentration was delayed approximately 30 minutes. Effects on the absorption of other beta-blockers have not been determined. Therefore, patients on propranolol should be observed when colestipol hydrochloride tablets are either added or deleted from a therapeutic regimen. Studies in humans show that the absorption of chlorothiazide as reflected in urinary excretion is markedly decreased even when administered one hour before colestipol hydrochloride. The absorption of tetracycline, furosemide, penicillin G, hydrochlorothiazide, and gemfibrozil was significantly decreased when given simultaneously with colestipol hydrochloride; these drugs were not tested to determine the effect of administration one hour before colestipol hydrochloride. No depressant effect on blood levels in humans was noted when colestipol hydrochloride was administered with any of the following drugs: aspirin, clindamycin, clofibrate, methyldopa, nicotinic acid (niacin), tolbutamide, phenytoin or warfarin. Particular caution should be observed with digitalis preparations since there are conflicting results for the effect of colestipol hydrochloride on the availability of digoxin and digitoxin. The potential for binding of these drugs if given concomitantly is present. Discontinuing colestipol hydrochloride could pose a hazard to health if a potentially toxic drug that is significantly bound to the resin has been titrated to a maintenance level while the patient was taking colestipol hydrochloride. Bile acid binding resins may also interfere with the absorption of oral phosphate supplements and hydrocortisone. A study has shown that cholestyramine binds bile acids and reduces mycophenolic acid exposure. As colestipol also binds bile acids, colestipol may reduce mycophenolic acid exposure and potentially reduce efficacy of mycophenolate mofetil.