Sentence: Combination of a betalactam antibiotic ( ampicillin or azlocillin ) or polymyxin B with rifampicin were studied with their administration in succession at various intervals in an experimental model of plague infection of albino mice .
Drug combination annotation:
[{'class': 'POS', 'spans': ['ampicillin', 'rifampicin'], 'is_context_needed': True}, {'class': 'POS', 'spans': [1, 3], 'is_context_needed': True}, {'class': 'POS', 'spans': [2, 3], 'is_context_needed': True}]