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: This change resulted within 2 - 4 weeks in the 50 - 200 % increase in the plasma levels of these neuroleptics and the appearance of extrapyramidal symptoms .
### Output Text:
This change resulted within 2 - 4 weeks in the 50 - 200 % increase in the plasma levels of these neuroleptics and the appearance of extrapyramidal symptoms . 