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: RESULTS : In the 12 patients switched because of chronic nephrotoxicity there was a significant decrease in serum creatinine [ 233 + / - 34 to 210 + / - 56 micromol / liter ( P < 0 . 05 ) at 6 months ] .
### Output Text:
RESULTS : In the 12 patients switched because of chronic nephrotoxicity there was a significant decrease in serum <span class="chemical">creatinine</span> [ 233 + / - 34 to 210 + / - 56 micromol / liter ( P < 0 . 05 ) at 6 months ] . 