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: Blood pressure effects of i . v . levodopa were examined in parkinsonian patients with stable and fluctuating responses to levodopa .
### Output Text:
Blood pressure effects of i . v . <span class="chemical">levodopa</span> were examined in parkinsonian patients with stable and fluctuating responses to <span class="chemical">levodopa</span> . 