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: The combination of a relatively high dose of clarithromycin in face of chronic renal failure in a functionally anephric patient , with underlying aluminum intoxication , may have facilitated the appearance of this neurotoxic side effect .
### Output Text:
The combination of a relatively high dose of <span class="chemical">clarithromycin</span> in face of chronic renal failure in a functionally anephric patient , with underlying <span class="chemical">aluminum</span> intoxication , may have facilitated the appearance of this neurotoxic side effect . 