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 investigated the efficacy and toxicity of a 3 - hour paclitaxel infusion in a phase II trial in patients with inoperable stage IIIB or IV NSCLC .
### Output Text:
We investigated the efficacy and toxicity of a 3 - hour <span class="chemical">paclitaxel</span> infusion in a phase II trial in patients with inoperable stage IIIB or IV NSCLC . 