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: This pharmacological profile is similar to those of mexiletine and tocainide , and all three drugs have central nervous system ( CNS ) stimulant action .
### Output Text:
This pharmacological profile is similar to those of <span class="chemical">mexiletine</span> and <span class="chemical">tocainide</span> , and all three drugs have central nervous system ( CNS ) stimulant action . 