Drug Interactions between citric acid/magnesium oxide/sodium picosulfate and Cystemms-V

GENERALLY AVOID: Agents that can alkalinize the urine such as thiazide diuretics, carbonic anhydrase inhibitors, and antacids may decrease the antibacterial effectiveness of methenamine by inhibiting its conversion to formaldehyde. Methenamine is most effectively converted in an acidic milieu of pH less than 5.5.

MANAGEMENT: Concomitant use of methenamine-containing preparations with thiazide diuretics, carbonic anhydrase inhibitors, or large doses of antacids should be avoided if possible. Otherwise, frequent urine pH testing may be considered. Some methenamine products may be used with antacids if dosing times are separated by at least one hour. Consult the manufacturer's product labeling for specific recommendations.

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GENERALLY AVOID: Theoretically, use of sodium picosulfate during or following antibiotic treatment may result in a reduced laxative effect of sodium picosulfate. The proposed mechanism involves antibiotic-induced reduction of colonic bacteria that hydrolyze sodium picosulfate, a prodrug, to its active metabolite bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM), a compound that stimulates colonic peristalsis. The clinical significance of this effect remains unknown.

MANAGEMENT: Consider use of an alternate laxative in patients who have recently taken or are currently taking an antibiotic. If concomitant use is required, additional bowel cleansing and colonoscopy may be required.

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MONITOR: Chronic administration of antacids may reduce serum salicylate concentrations in patients receiving large doses of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to urinary alkalinization by antacids, resulting in increased renal salicylate clearance. In three children treated with large doses of aspirin for rheumatic fever, serum salicylate levels declined 30% to 70% during coadministration with a magnesium and aluminum hydroxide antacid. Other studies have found similar, albeit less dramatic results. Antacids reportedly have no effect on the oral bioavailability of aspirin in healthy adults. However, administration of antacids containing either aluminum and magnesium hydroxide or calcium carbonate two hours before aspirin dosing led to reduced absorption of aspirin in uremic patients.

MANAGEMENT: Patients treated chronically with antacids (or oral medications that contain antacids such as didanosine buffered tablets or pediatric oral solution) and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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MONITOR: Coadministration with agents that affect renal function or perfusion such as diuretics, ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk and/or severity of fluid and electrolyte disturbances associated with the use of bowel cleansing preparations. Fluid and electrolyte disturbances can lead to serious adverse events including cardiac arrhythmias, seizures, and renal impairment.

MANAGEMENT: Caution is advised when bowel cleansing preparations are used in patients treated with agents that affect renal function or perfusion, particularly if they are frail or elderly or have preexisting renal impairment. Baseline and postprocedure labs including serum electrolytes, BUN, and creatinine should be considered. Patients should be advised to drink sufficient quantities of clear fluids before, during, and after bowel cleansing. Hospitalization and intravenous fluid hydration may be appropriate for frail or elderly patients who may be unable to drink an adequate volume of fluid.

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