Sentence: To study the release of free endotoxin from Escherichia coli exposed to varying concentrations of the penicillin-binding protein ( PBP ) 3-specific beta-lactam antibiotic cefuroxime , the aminoglycoside tobramycin , and a combination of the two , and to test the relationship between bacterial killing rate and endotoxin release .
Drug combination annotation:
[{'class': 'POS', 'spans': ['cefuroxime', 'tobramycin'], 'is_context_needed': True}]