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: Pain at the injection site occurred in 35 % ( 22 of 62 ) of patients in the diazepam group compared with 7 % ( 4 of 60 patients ) in the midazolam group ( p < 0 . 001 ) .
### Output Text:
Pain at the injection site occurred in 35 % ( 22 of 62 ) of patients in the <span class="chemical">diazepam</span> group compared with 7 % ( 4 of 60 patients ) in the <span class="chemical">midazolam</span> group ( p < 0 . 001 ) . 