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: If confirmed in controlled trials , the long - term results of this open , non - randomized study might indicate that the analgesic effect of capsaicin in PHN is mediated by both interference with neuropeptide metabolism and morphological changes ( perhaps degeneration ) of nociceptive afferents .
### Output Text:
If confirmed in controlled trials , the long - term results of this open , non - randomized study might indicate that the analgesic effect of <span class="chemical">capsaicin</span> in PHN is mediated by both interference with neuropeptide metabolism and morphological changes ( perhaps degeneration ) of nociceptive afferents . 