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: In this latter patient , and in 2 others , the causal relationship between methyldopa and hepatic dysfunction was proved with the recurrence of hepatitis within 2 weeks of re - exposure to the drug .
### Output Text:
In this latter patient , and in 2 others , the causal relationship between <span class="chemical">methyldopa</span> and hepatic dysfunction was proved with the recurrence of hepatitis within 2 weeks of re - exposure to the drug . 