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: Following polytherapy according to the CMF regimen , a statistically significant decrease ( p = 0 . 0343 ) in creatinine clearance was found , but creatinine concentration did not increase significantly compared to controls .
### Output Text:
Following polytherapy according to the CMF regimen , a statistically significant decrease ( p = 0 . 0343 ) in <span class="chemical">creatinine</span> clearance was found , but <span class="chemical">creatinine</span> concentration did not increase significantly compared to controls . 