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: Therefore , concomitant administration of small doses of bradykinin receptor antagonists and NO synthase inhibitors can be effective in alleviation of neuropathic pain , even in hospital care .
### Output Text:
Therefore , concomitant administration of small doses of <span class="chemical">bradykinin</span> receptor antagonists and <span class="chemical">NO</span> synthase inhibitors can be effective in alleviation of neuropathic pain , even in hospital care . 