Acetazolamide-Accelerated Anticonvulsant Osteomalacia

Severe osteomalacia was present in two epileptic patients who were under long-term treatment with congeners of phenytoin, phenobarbital, and acetazolamide. These patients showed slightly low serum calcium, normal or low serum phosphate, and normal parathyroid hormone concentrations. Discontinuation of acetazolamide produced an immediate threefold drop in the level of urinary calcium excretion and a slight rise in tubular reabsorption of phosphate, with no dectectable change in serum calcium or phosphate concentrations. Acetazolamide may have accelerated the development of osteomalacia by several mechanisms, including increased renal calcium excretion.