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: Patients in group B were not comparable to those in group A , as the latter were medically compromised and were receiving multiple pharmacotherapies .
### Output Text:
Patients in group B were not comparable to those in group A , as the latter were medically compromised and were receiving multiple pharmacotherapies . 