Systemic administration of calcitonin through ocular route

Calcitonin has been used clinically to treat hypercalcemia, Vitamin D intoxication, osteolytic bone metastases and increased skeletal remodeling in Paget's disease. In general calcitonin is given every 6 to 12 hrs intramuscularly or subcutaneously. It has been found in this study that the same results can be achieved by giving calcitonin through eyes as ophthalmic solutions. When 25 microliters of 0.05% calcitonin was given as eyedrops to New Zealand white rabbits, it did not reach the concentration achieved by i.v. administration at the same dose level. The systemic absorption of calcitonin did not reach the level achieved by i.v. administration even though the eyedrop concentrations were increased 2-fold (0.1%) to 10-fold (0.5%). When absorption enhancers such as BL-9 and Brij-78 were added to calcitonin eyedrops, however, the systemic absorption of calcitonin was enhanced markedly. BL-9 (0.5%) increased calcitonin (0.5%) absorption 16-20 fold and raised blood concentration of calcitonin above levels achieved by i.v. injection (25 microliters, 0.05%) with 0.5% calcitonin eyedrops instillation. Effects of Brij-78 (0.5%) were even more impressive. It increases calcitonin absorption 22-24 fold and raised the blood concentration of calcitonin above the levels achieved by i.v. injection (25 microliters 0.05%) with 0.15% and 0.5% calcitonin eyedrops instillation. These results indicate that the therapeutic level of calcitonin can be reached through the ocular route.