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: Metformin was injected intraperitoneally in dose of 200mg / kg along with alternate - day PTZ .
### Output Text:
<span class="chemical">Metformin</span> was injected intraperitoneally in dose of 200mg / kg along with alternate - day <span class="chemical">PTZ</span> . 