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: CNS complications included posterior reversible leukoencephalopathy syndrome ( n = 10 ) , stroke ( n = 5 ) , temporal lobe epilepsy ( n = 2 ) , high - dose methotrexate toxicity ( n = 2 ) , syndrome of inappropriate antidiuretic hormone secretion ( n = 1 ) , and other unclassified events ( n = 7 ) .
### Output Text:
CNS complications included posterior reversible leukoencephalopathy syndrome ( n = 10 ) , stroke ( n = 5 ) , temporal lobe epilepsy ( n = 2 ) , high - dose <span class="chemical">methotrexate</span> toxicity ( n = 2 ) , syndrome of inappropriate antidiuretic hormone secretion ( n = 1 ) , and other unclassified events ( n = 7 ) . 