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: In order to evaluate the efficacy , time - course of action and predictors of response to topical capsaicin , 39 patients with chronic post - herpetic neuralgia ( PHN ) , median duration 24 months , were treated with 0 . 025 % capsaicin cream for 8 weeks .
### Output Text:
In order to evaluate the efficacy , time - course of action and predictors of response to topical <span class="chemical">capsaicin</span> , 39 patients with chronic post - herpetic neuralgia ( PHN ) , median duration 24 months , were treated with 0 . 025 % <span class="chemical">capsaicin</span> cream for 8 weeks . 