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: Topical 0 . 025 % capsaicin in chronic post - herpetic neuralgia : efficacy , predictors of response and long - term course .
### Output Text:
Topical 0 . 025 % <span class="chemical">capsaicin</span> in chronic post - herpetic neuralgia : efficacy , predictors of response and long - term course . 