Pena-Miller et al present interesting data. However combination of erythromycin with doxycyclin is, when at all, very rarely prescribed. More interesting would be investigating effects of the most widely used combinations such as amoxicillin + clavulanic acid or piperacillin + tazobactam. Both of these inhibitors are possess not only antibacterial activity but are also potent inducers of beta-lactamases.
The extended spectrum betalactamases producing strains have emerged not only due to extensive use of group three cephalosporins (e.g. cefotaxime, ceftazidime etc.) but also due to uncritical use of beta-lactams in combination with beta-lactamse inhibitors such as clavulanic acid or tazobactam.
To my knowledge there are at least eight combination products (group three cephalosporines + beta-lactamase inhibitors) marketed in the Indian subcontinent. NDM producing strains may have resulted from extensive use of such drug-combinations.
