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: Second , we investigated the effect of IT MK - 801 ( 30 mug ) on the histopathologic changes in the spinal cord after morphine - induced spastic paraparesis .
### Output Text:
Second , we investigated the effect of IT <span class="chemical">MK - 801</span> ( 30 mug ) on the histopathologic changes in the spinal cord after <span class="chemical">morphine</span> - induced spastic paraparesis . 