Imipenem is given in combination with cilastatin, a specific inhibitor of the renal enzyme dehydropeptidase-1 that inactivates imipenem. Imipenem has been widely replaced by meropenem. Imipenem has an extremely wide spectrum of activity, including most aerobic and anaerobic Gram-negative, including those expressing extended-spectrum beta-lactamases (ESBLs), and Gram-positive bacteria (but not MRSA). It has no activity against Stenotrophomonas maltophilia, which emerges in some patients treated with imipenem. Acquired resistance is relatively common in Pseudomonas aeruginosa and is starting to emerge in some of the Enterobacteriaceae, including Enterobacter spp., Citrobacter spp. and Proteus spp.