Drug-induced disorders of bone metabolism. Incidence, management and avoidance.

Calcium homeostasis depends upon the interplay of intestinal calcium absorption, renal excretion and skeletal mobilisation of calcium, mediated through bone formation and resorption, which are closely coupled in the adult skeleton. Serum calcium is extremely important for maintenance of normal cellular functions and is regulated by the major calciotropic hormones, parathyroid hormone (PTH), 1,25-dihydroxy-vitamin D and calcitonin. Certain drugs can interfere with calcium metabolism by effects at different stages in calcium metabolism, and a knowledge of the mechanism of drug action is generally helpful in understanding the various resultant clinical skeletal syndromes. Corticosteroids, for example, have profound effects at multiple stages of calcium metabolism, resulting in decreased bone formation and enhanced bone resorption leading to accelerated osteoporosis. Drugs such as aluminium and anticonvulsants impair mineralisation, leading to osteomalacia. Other drugs, such as fluoride, are employed for their known effects on bone, but in excess dosage can be harmful by producing mineralisation defects. Management of these conditions will be discussed in this review.