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: Therefore , patients belonging to the poor - metabolizer phenotype of sparteine / debrisoquine polymorphism in drug metabolism , which constitutes 6 . 4 % of the German population , may experience adverse drug reactions when treated with standard doses of one of these drugs alone .
### Output Text:
Therefore , patients belonging to the poor - metabolizer phenotype of <span class="chemical">sparteine</span> / <span class="chemical">debrisoquine</span> polymorphism in drug metabolism , which constitutes 6 . 4 % of the German population , may experience adverse drug reactions when treated with standard doses of one of these drugs alone . 