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 multivariate analysis showed that severe MR , MP ( EF < 45 % ) and high doses of MZ ( > 5mg ) were associated with events ( p < 0 . 001 ) .
### Output Text:
The multivariate analysis showed that severe MR , MP ( EF < 45 % ) and high doses of <span class="chemical">MZ</span> ( > 5mg ) were associated with events ( p < 0 . 001 ) . 