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: Twenty children with acute lymphoblastic leukemia who developed meningeal disease were treated with a high - dose intravenous methotrexate regimen that was designed to achieve and maintain CSF methotrexate concentrations of 10 ( - 5 ) mol / L without the need for concomitant intrathecal dosing .
### Output Text:
Twenty children with acute lymphoblastic leukemia who developed meningeal disease were treated with a high - dose intravenous <span class="chemical">methotrexate</span> regimen that was designed to achieve and maintain CSF <span class="chemical">methotrexate</span> concentrations of 10 ( - 5 ) mol / L without the need for concomitant intrathecal dosing . 