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: Only five patients experienced blood disorders , one of whom was exposed to TMP - SMZ ; of seven with erythema multiforme and Stevens - Johnson syndrome , four were exposed to TMP - SMZ .
### Output Text:
Only five patients experienced blood disorders , one of whom was exposed to <span class="chemical">TMP - SMZ</span> ; of seven with erythema multiforme and Stevens - Johnson syndrome , four were exposed to <span class="chemical">TMP - SMZ</span> . 