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: We recommend caution in the use of lopinavir / ritonavir in the immediate neonatal period .
### Output Text:
We recommend caution in the use of <span class="chemical">lopinavir / ritonavir</span> in the immediate neonatal period . 