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: Variables evaluated included patient weight , age , sex , serum creatinine level , creatinine clearance , duration of therapy , total dose , mean daily dose , organism minimum inhibitory concentration ( MIC ) , mean peak levels , mean trough levels , mean area under the serum concentration - time curve ( AUC ) , total AUC , mean AUC greater than MIC , total AUC greater than MIC , mean Schumacher ' s intensity factor ( IF ) , total IF , In ( mean maximum concentration [ Cmax ] / MIC ) .
### Output Text:
Variables evaluated included patient weight , age , sex , serum <span class="chemical">creatinine</span> level , <span class="chemical">creatinine</span> clearance , duration of therapy , total dose , mean daily dose , organism minimum inhibitory concentration ( MIC ) , mean peak levels , mean trough levels , mean area under the serum concentration - time curve ( AUC ) , total AUC , mean AUC greater than MIC , total AUC greater than MIC , mean Schumacher ' s intensity factor ( IF ) , total IF , In ( mean maximum concentration [ Cmax ] / MIC ) . 