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: We conducted a population - based 45 - day follow - up study of 232 , 390 people who were prescribed trimethoprim - sulfamethoxazole ( TMP - SMZ ) , 266 , 951 prescribed trimethoprim alone , and 196 , 397 prescribed cephalexin , to estimate the risk of serious liver , blood , skin , and renal disorders resulting in referral or hospitalization associated with these drugs .
### Output Text:
We conducted a population - based 45 - day follow - up study of 232 , 390 people who were prescribed <span class="chemical">trimethoprim - sulfamethoxazole</span> ( <span class="chemical">TMP - SMZ</span> ) , 266 , 951 prescribed <span class="chemical">trimethoprim</span> alone , and 196 , 397 prescribed <span class="chemical">cephalexin</span> , to estimate the risk of serious liver , blood , skin , and renal disorders resulting in referral or hospitalization associated with these drugs . 