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: A history of drug exposure also was taken with special attention on the use of antidepressants , anorexigens , and amphetamines .
### Output Text:
A history of drug exposure also was taken with special attention on the use of antidepressants , anorexigens , and <span class="chemical">amphetamines</span> . 