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: Overall , venous complications were more frequent with diazepam ( 22 of 62 patients ) than with midazolam ( 4 of 60 patients ) ( p < 0 . 001 ) .
### Output Text:
Overall , venous complications were more frequent with <span class="chemical">diazepam</span> ( 22 of 62 patients ) than with <span class="chemical">midazolam</span> ( 4 of 60 patients ) ( p < 0 . 001 ) . 