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: When circumflex artery blood flow was maintained constant , the increases in CxAD induced by cromakalim ( 10 micrograms / kg ) , pinacidil ( 30 micrograms / kg ) and nitroglycerin ( 10 micrograms / kg ) were reduced by 68 + / - 7 , 54 + / - 9 and 1 + / - 1 % , respectively .
### Output Text:
When circumflex artery blood flow was maintained constant , the increases in CxAD induced by <span class="chemical">cromakalim</span> ( 10 micrograms / kg ) , <span class="chemical">pinacidil</span> ( 30 micrograms / kg ) and <span class="chemical">nitroglycerin</span> ( 10 micrograms / kg ) were reduced by 68 + / - 7 , 54 + / - 9 and 1 + / - 1 % , respectively . 