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: CONCLUSIONS : Careful administration is necessary in patients > or = 60 years old , in female patients , and in patients receiving a ribavirin dose of 12 mg / kg or more .
### Output Text:
CONCLUSIONS : Careful administration is necessary in patients > or = 60 years old , in female patients , and in patients receiving a <span class="chemical">ribavirin</span> dose of 12 mg / kg or more . 