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: In animals with normal renal function , OCT induced a transient decrease in serum PTH levels at a dose of 0 . 1 microg / kg , which was not sustained with lowering of the doses .
### Output Text:
In animals with normal renal function , <span class="chemical">OCT</span> induced a transient decrease in serum PTH levels at a dose of 0 . 1 microg / kg , which was not sustained with lowering of the doses . 