Drug Interactions between Marblen and meperidine / promethazine

ADJUST DOSE: The central nervous system and respiratory depressant effects of meperidine may be potentiated by concomitant use of other agents with CNS depressant effects. An increased risk of serious adverse reactions such as respiratory depression, hypotension, profound sedation, syncope, coma, and even death should be considered, particularly in elderly or debilitated patients.

MANAGEMENT: Caution and dosage adjustments are advisable when meperidine is used in combination with other narcotic analgesics, general anesthetics, phenothiazines, sedative-hypnotics, tranquilizers, tricyclic antidepressants, or other CNS depressants such as alcohol. A lower dosage of meperidine should be considered initially, then titrated carefully according to pain level and clinical response. Meperidine dosage reductions of 25% to 50% have been recommended for patients receiving phenothiazines and other tranquilizers. Patients should be advised to avoid rising abruptly from a sitting or recumbent position, and to notify their physician if they experience dizziness, lightheadedness, orthostasis, syncope, tachycardia, or excessive CNS effects that interfere with their normal activities. Patients should also avoid driving or operating hazardous machinery until they know how these medications affect them.

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Coadministration with aluminum- or magnesium-containing antacids may decrease the serum concentrations of orally administered phenothiazines. The proposed mechanism is antacid adsorption resulting in reduced phenothiazine bioavailability. The interaction has been reported for chlorpromazine but may occur with other phenothiazines. In a study of ten patients treated with chlorpromazine, 30 mL of an antacid containing aluminum and magnesium hydroxide reduced the urinary excretion of chlorpromazine by 10% to 45%. In another study with six psychiatric patients, coadministration of chlorpromazine oral suspension with 30 mL of an antacid containing aluminum hydroxide and magnesium trisilicate resulted in a 20% reduction in serum chlorpromazine level two hours later. The clinical significance is unknown. Psychiatric relapse occurred in a chlorpromazine-treated patient following the addition of antacid therapy according to a single case report. Separating the times of administration by 2 to 3 hours may help if an interaction is suspected.

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