Drug Interactions between Aralen Phosphate and citric acid/magnesium oxide/sodium picosulfate

ADJUST DOSING INTERVAL: Concomitant administration of antacids or kaolin may reduce the oral bioavailability of chloroquine. The proposed mechanism is adsorption of chloroquine by polyvalent cations present in these agents. Delayed dissolution of chloroquine tablets in the presence of antacids may also be a contributing factor. In six healthy study subjects, administration of a single 1 gram dose of chloroquine phosphate in combination with a 1 gram dose of magnesium trisilicate or kaolin decreased chloroquine systemic exposure (AUC) by approximately 18% and 29%, respectively, compared to administration alone. In vitro evidence of the interaction has also been reported for other antacids including calcium carbonate and gerdiga. The clinical significance has not been established.

MANAGEMENT: Chloroquine product labeling suggests separating the doses by at least 4 hours if concomitant therapy with antacids or kaolin is required. The same precaution may be applicable to hydroxychloroquine, although no data are available to support this recommendation. Some authorities recommend separating the dose of hydroxychloroquine from antacids and kaolin by at least 2 hours (AU).

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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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