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: Prolactin responses to verapamil in 65 female patients ( age : 29 . 9 + / - 8 . 1 years ) with hyperprolactinemia were tested in a descriptive , matched case - control study .
### Output Text:
Prolactin responses to <span class="chemical">verapamil</span> in 65 female patients ( age : 29 . 9 + / - 8 . 1 years ) with hyperprolactinemia were tested in a descriptive , matched case - control study . 