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: METHODS : Eighty - eight patients with chronic hepatitis C who received interferon - alpha - 2b at a dose of 6 MU administered intramuscularly for 24 weeks in combination with ribavirin administered orally at a dose of 600 mg or 800 mg participated in the study .
### Output Text:
METHODS : Eighty - eight patients with chronic hepatitis C who received <span class="chemical">interferon - alpha - 2b</span> at a dose of 6 MU administered intramuscularly for 24 weeks in combination with <span class="chemical">ribavirin</span> administered orally at a dose of 600 mg or 800 mg participated in the study . 