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: With respect to hemoglobin level at the time of ribavirin reduction , a rate of continuation of therapy in patients with > or = 10 g / dl hemoglobin was higher than that in patients with < 10 g / dl ( P = 0 . 036 ) .
### Output Text:
With respect to hemoglobin level at the time of <span class="chemical">ribavirin</span> reduction , a rate of continuation of therapy in patients with > or = 10 g / dl hemoglobin was higher than that in patients with < 10 g / dl ( P = 0 . 036 ) . 