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 authors conclude that in a patient starting DPH treatment an unexpected increase in seizures , with EEG and mental changes occurring simultaneously , should alert the physician to the possible need for eliminating DPH from the therapeutic regimen , even if plasma concentrations are low .
### Output Text:
The authors conclude that in a patient starting <span class="chemical">DPH</span> treatment an unexpected increase in seizures , with EEG and mental changes occurring simultaneously , should alert the physician to the possible need for eliminating <span class="chemical">DPH</span> from the therapeutic regimen , even if plasma concentrations are low . 