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: Analysis of protein expression using antibody microarrays and Western blotting revealed differential changes in MAP kinase - related pathways after multiple and single METH injections .
### Output Text:
Analysis of protein expression using antibody microarrays and Western blotting revealed differential changes in MAP kinase - related pathways after multiple and single <span class="chemical">METH</span> injections . 