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: A 51 year old man took a mixed overdose including 1 . 8 - 3 . 6 g of diltiazem , paracetamol , aspirin , isosorbide nitrate , and alcohol .
### Output Text:
A 51 year old man took a mixed overdose including 1 . 8 - 3 . 6 g of <span class="chemical">diltiazem</span> , <span class="chemical">paracetamol</span> , <span class="chemical">aspirin</span> , <span class="chemical">isosorbide</span> <span class="chemical">nitrate</span> , and <span class="chemical">alcohol</span> . 