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: Sixty - five patients , 34 women and 31 men , ages 36 to 80 years , received either normal saline before and after TDI ( group 1 ) , 125 mg i . v . MP before and saline after TDI ( group 2 ) , or 125 mg i . v . MP before and after TDI ( group 3 ) .
### Output Text:
Sixty - five patients , 34 women and 31 men , ages 36 to 80 years , received either normal saline before and after TDI ( group 1 ) , 125 mg i . v . <span class="chemical">MP</span> before and saline after TDI ( group 2 ) , or 125 mg i . v . <span class="chemical">MP</span> before and after TDI ( group 3 ) . 