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: Serum blood urea and creatinine concentrations increased significantly in rats given an iv infusion of D - AmB 3 mg / kg but not in those given the same dose of NS - 718 .
### Output Text:
Serum blood <span class="chemical">urea</span> and <span class="chemical">creatinine</span> concentrations increased significantly in rats given an iv infusion of <span class="chemical">D - AmB</span> 3 mg / kg but not in those given the same dose of NS - 718 . 