Drug Interactions between citric acid/magnesium oxide/sodium picosulfate and PC-CAP

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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MONITOR: The risk of seizures induced by the use of bowel cleansing preparations may be increased in patients on concomitant medications that can lower the seizure threshold, including psychotherapeutic agents (antidepressants; neuroleptics; lithium), fluoroquinolones, some antimalarial agents (chloroquine; hydroxychloroquine; mefloquine), and some narcotic analgesics. Rare cases of generalized tonic-clonic seizures and/or loss of consciousness in association with low serum osmolality and electrolyte abnormalities (e.g., hyponatremia, hypokalemia, hypocalcemia, hypomagnesemia) have been reported with the use of bowel cleansing products in patients with no prior history of seizures. The condition resolved with correction of fluid and electrolyte abnormalities.

MONITOR: The use of bowel cleansing preparations may increase the risk of ventricular arrhythmia, particularly torsade de pointes, in patients treated with drugs that can prolong the QT interval, including psychotherapeutic agents (antidepressants; neuroleptics; lithium), fluoroquinolones, some antimalarial agents (chloroquine; mefloquine; halofantrine; lumefantrine), and some narcotic analgesics (methadone; propoxyphene). Severe and potentially fatal cases of electrolyte disorders and arrhythmias have been reported in elderly patients using bowel cleansing products. Electrolyte disturbances such as hypokalemia and hypomagnesemia are known risk factors for torsade de pointes associated with QT interval prolongation.

MANAGEMENT: Caution is advised when bowel cleansing preparations are prescribed in patients treated with agents that can lower the seizure threshold and/or prolong the QT interval. Bowel cleansing preparations should not be used if these patients have impaired renal function or perfusion, dehydration, or uncorrected electrolyte abnormalities. Baseline and postprocedure labs including serum electrolytes, phosphate, BUN, and creatinine should be considered, particularly in the elderly. Patients should be advised not to exceed the recommended dosage of their bowel cleansing preparation and to drink sufficient quantities of clear fluids before, during, and after the bowel preparation process. Administration of an electrolyte rehydration solution may help attenuate the electrolyte abnormalities and hypovolemia. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

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One study has reported that coadministration of caffeine and aspirin lead to a 25% increase in the rate of appearance and 17% increase in maximum concentration of salicylate in the plasma. A significantly higher area under the plasma concentration time curve of salicylate was also reported when both drugs were administered together. The exact mechanism of this interaction has not been specified. Physicians and patients should be aware that coadministration of aspirin and caffeine may lead to higher salicylate levels faster.

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