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: The high prevalence of anorexigen use in patients with SPH also raises the possibility that these drugs precipitate pulmonary hypertension in patients with underlying conditions associated with SPH .
### Output Text:
The high prevalence of anorexigen use in patients with SPH also raises the possibility that these drugs precipitate pulmonary hypertension in patients with underlying conditions associated with SPH . 