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: Symptoms persisted for three months despite TAC dose reduction , administration of IVIG and four doses of methylprednisolone pulse therapy .
### Output Text:
Symptoms persisted for three months despite <span class="chemical">TAC</span> dose reduction , administration of IVIG and four doses of <span class="chemical">methylprednisolone</span> pulse therapy . 