Drug Interactions between calcium / ferrous fumarate / vitamin d and halazepam

ADJUST DOSING INTERVAL: The bioavailability of orally administered iron may be reduced by concomitant administration of antacids or other agents with acid-neutralizing effects. The exact mechanism is unknown but may involve reduced iron solubility due to increase in gastric pH and/or reduced absorption due to complexation or precipitation of the iron. Based on existing data, sodium bicarbonate and calcium carbonate appear to have greater effects than antacids containing magnesium and aluminum hydroxides. In a study of patients with mild iron deficiency anemia, coadministration of ferrous sulfate with sodium bicarbonate 1 gram and calcium carbonate 500 mg reduced iron absorption by 50% and 67%, respectively, while 5 mL of an antacid containing magnesium and aluminum hydroxides had little effect. Another study also found no effect on iron absorption when ferrous sulfate (equivalent to 10 mg/kg of elemental iron) was coadministered with magnesium hydroxide (1 mg for every 5 mg of elemental iron ingested) in a group of healthy, fasting male subjects. In contrast, absorption of iron from ferrous sulfate and ferrous fumarate tablets was reduced by 37% and 31%, respectively, following administration of an antacid containing magnesium carbonate, magnesium hydroxide, and aluminum hydroxide in a study of healthy, iron-replete volunteers. Similarly, in a study of nine patients, coadministration of 5 mg of ferrous sulfate with a 35 gram dose of magnesium trisilicate was found to reduce iron absorption by an average of more than 70%. The interaction reportedly does not occur in the presence of ascorbic acid, which may competitively bind with iron and prevent the interference with iron absorption.

MANAGEMENT: To minimize the potential for interaction, it may be appropriate to administer oral iron preparations at least two hours apart from antacids or other agents with acid-neutralizing effects.

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A number of studies have reported that antacids can delay the gastrointestinal absorption and reduce the peak plasma concentration (Cmax) of some benzodiazepines, including clorazepate, chlordiazepoxide and diazepam, although the overall extent of absorption is generally not affected. The exact mechanism of interaction is unknown, but may involve delayed gastric emptying or cation binding of the benzodiazepine. As a result, benzodiazepine onset of action may be delayed and clinical effects diminished. However, one study reported a significant increase in diazepam absorption during coadministration with aluminum hydroxide, and there was a marginal increase in the onset of sedative effect. Aluminum hydroxide also increased triazolam Cmax and systemic exposure (AUC) in 11 dialysis patients such that their drug levels reached into the range observed for the matched controls. In contrast, another study by the same group of investigators found no significant effect of aluminum hydroxide on temazepam absorption or Cmax in 11 patients with end-stage renal disease. A multi-dose study also failed to find an effect of antacids on the steady-state levels of N-desmethyldiazepam, the active metabolite of clorazepate, although an acidic environment is thought to be necessary for the rapid conversion. Based on available data, the clinical significance of this interaction appears to be minor. As a precaution, patients may consider separating the administration times of benzodiazepines and antacids or other oral medications that contain antacids (e.g., didanosine buffered tablets or pediatric oral solution) by 2 to 3 hours.

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