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: Three of the 4 patients were taking less than 6 . 5 mg / kg per day and all patients had normal renal and liver function test results .
### Output Text:
Three of the 4 patients were taking less than 6 . 5 mg / kg per day and all patients had normal renal and liver function test results . 