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: The antiarrhythmic effects of the sustained release form of mexiletine ( Mexitil - Perlongets ) were evaluated in a double - blind placebo trial in 630 patients with recent documented myocardial infarction .
### Output Text:
The antiarrhythmic effects of the sustained release form of <span class="chemical">mexiletine</span> ( <span class="chemical">Mexitil - Perlongets</span> ) were evaluated in a double - blind placebo trial in 630 patients with recent documented myocardial infarction . 