Magnesium hydroxide withdrawal

Two patients with hypothyroidism taking a fixed dosage of levothyroxine took aluminium hydroxide and magnesium oxide (72). In both cases there was a marked increase in the serum concentration of TSH and low serum T4. After withdrawal of the antacids, TSH again fell. In vitro studies showed a dose-related adsorption of levothyroxine by a combination of aluminium hydroxide, magnesium hydroxide, and magnesium carbonate, but no effect of magnesium oxide alone. 

A 39-year-old woman who took high doses of aluminium and magnesium hydroxide for peptic ulcer disease (over 18 kg of elemental aluminium and 15 kg of elemental magnesium over 8 years) developed severe osteomalacia due to profound phosphate depletion (60). Bone biopsy showed stainable aluminium deposits along 28% of the total bone surface, a unique observation in a patient with normal renal function. Treatment included withdrawal of the antacid and supplementation with phosphate, calcium, and vitamin D. Her bone mineral density increased over the next 2 years. 

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