In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: CONCLUSIONS : These results indicate that even though OCT does not completely prevent the occurrence of hypercalcemia in experimental dogs with renal insufficiency , it may be of use in the management of secondary hyperparathyroidism because it does not induce low bone turnover and , therefore , does not increase the risk of adynamic bone disease .
### Output Text:
CONCLUSIONS : These results indicate that even though <span class="chemical">OCT</span> does not completely prevent the occurrence of hypercalcemia in experimental dogs with renal insufficiency , it may be of use in the management of secondary hyperparathyroidism because it does not induce low bone turnover and , therefore , does not increase the risk of adynamic bone disease . 