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: A selective antagonist of mGluR5 , 2 - methyl - 6 - ( phenylethynyl ) pyridine ( MPEP ; 5 mg / kg ip ) , when administered five times immediately before each methamphetamine injection reversed the above - mentioned methamphetamine effects .
### Output Text:
A selective antagonist of mGluR5 , <span class="chemical">2 - methyl - 6 - ( phenylethynyl ) pyridine</span> ( <span class="chemical">MPEP</span> ; 5 mg / kg ip ) , when administered five times immediately before each <span class="chemical">methamphetamine</span> injection reversed the above - mentioned <span class="chemical">methamphetamine</span> effects . 