A patient with hypothyroidism who was euthyroid on a fixed-dosage, long-term 
maintenance regimen of levothyroxine sodium developed persistently elevated 
serum thyrotropin levels while receiving an aluminum hydroxide-containing 
antacid. The thyrotropin levels returned to normal shortly after cessation of 
the antacid therapy. These observations indicate that aluminum hydroxide may 
interfere with the bioavailability of thyroxine. The thyroid function of 
patients who are receiving replacement or suppressive thyroxine therapy should 
be monitored following the commencement of concurrent treatment with medications 
containing aluminum hydroxide.