Calcitriol. A review of its use in the treatment of postmenopausal osteoporosis and its potential in corticosteroid-induced osteoporosis.

A synthetic form of calcitriol (1,25-dihydroxycholecalciferol; 1,25-dihydroxyvitamin D3), the most physiologically active metabolite of vitamin D, has shown efficacy in the treatment of postmenopausal osteoporosis and promise in corticosteroid-induced osteoporosis. Although results of small studies investigating calcitriol in the treatment of postmenopausal osteoporosis have been conflicting, a clinical trial in 622 women with postmenopausal osteoporosis demonstrated that patients with mild to moderate disease who received calcitriol (0.25 microgram twice daily) had a significant 3-fold lower rate of new vertebral fractures after 3 years of treatment, compared with patients receiving elemental calcium 1000 mg/day. In patients commencing long term treatment with prednisone or prednisolone, calcitriol 0.5 to 1.0 micrograms/day plus calcium 1000 mg/day, administered with or without intranasal calcitonin 400 IU/day, prevented steroid-induced bone loss. Overall, calcitriol is well tolerated. As shown in clinical studies, at recommended dosages hypercalcaemia is infrequent and mild, generally responding to reductions in calcium intake and/or calcitriol dosage. The narrow 'therapeutic window' of calcitriol requires that its use be adequately supervised, with periodic monitoring of serum calcium and creatinine levels. However, significant renal toxicity has not been seen in patients with osteoporosis treated with calcitriol in high dosages for several years in comparative and noncomparative trials. In conclusion, as with other drugs currently used in the management of patients with osteoporosis, questions remain to be answered regarding the efficacy of calcitriol relative to other agents, and its tolerability in such patients during the very long term. Nonetheless, at this stage, calcitriol should be considered a useful treatment option in patients with mild to moderate postmenopausal osteoporosis.