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: Methyldopa is an antihypertensive medication which is available generically and under the trade name Aldomet that is widely prescribed in the adult population and infrequently used in children .
### Output Text:
<span class="chemical">Methyldopa</span> is an antihypertensive medication which is available generically and under the trade name <span class="chemical">Aldomet</span> that is widely prescribed in the adult population and infrequently used in children . 