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: Methamphetamine ( MA ) - induced dopaminergic neurotoxicity is believed to be associated with the increased formation of free radicals .
### Output Text:
<span class="chemical">Methamphetamine</span> ( <span class="chemical">MA</span> ) - induced dopaminergic neurotoxicity is believed to be associated with the increased formation of free radicals . 