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: One of the twins developed complete heart block and dilated cardiomyopathy related to lopinavir / ritonavir therapy , a boosted protease - inhibitor agent , while the other twin developed mild bradycardia .
### Output Text:
One of the twins developed complete heart block and dilated cardiomyopathy related to <span class="chemical">lopinavir / ritonavir</span> therapy , a boosted protease - inhibitor agent , while the other twin developed mild bradycardia . 