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: A detailed clinical history , together with skin tests , RAST ( radioallergosorbent test ) , and controlled challenge tests , was used to establish whether patients allergic to beta - lactam antibiotics had selective immediate allergic responses to amoxicillin ( AX ) or were cross - reacting with other penicillin derivatives .
### Output Text:
A detailed clinical history , together with skin tests , RAST ( radioallergosorbent test ) , and controlled challenge tests , was used to establish whether patients allergic to <span class="chemical">beta - lactam</span> antibiotics had selective immediate allergic responses to <span class="chemical">amoxicillin</span> ( <span class="chemical">AX</span> ) or were cross - reacting with other <span class="chemical">penicillin</span> derivatives . 