Effects of theophylline and salbutamol on phosphate and calcium metabolism in normal subjects.

The acute effects of oral theophylline and salbutamol were studied in a randomised double-blind crossover study in 12 normal subjects. Theophylline resulted in a significant fall in plasma phosphate and a small rise in urine phosphate excretion which did not, however, account for the fall in plasma phosphate. The increase in urine phosphate excretion was accompanied by a rise in sodium, calcium and water excretion. These changes were not accompanied by a change in renal cyclic AMP production, plasma parathyroid hormone levels or plasma calcitonin levels. Salbutamol had only minor effects on urine calcium and phosphate excretion.