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: Ibuprofen , sulindac , mefenamic acid , and low dose meclofenamic acid increased the latency - to - onset in the flurothyl and / or PTZ models ; the electroshock , picrotoxin and bicuculline models were not significantly affected by any of the pretreatment agents .
### Output Text:
<span class="chemical">Ibuprofen</span> , <span class="chemical">sulindac</span> , <span class="chemical">mefenamic acid</span> , and low dose <span class="chemical">meclofenamic acid</span> increased the latency - to - onset in the <span class="chemical">flurothyl</span> and / or <span class="chemical">PTZ</span> models ; the electroshock , <span class="chemical">picrotoxin</span> and <span class="chemical">bicuculline</span> models were not significantly affected by any of the pretreatment agents . 