Ceftazidime, sold under the brand names Fortaz and Tazicef, is an antibiotic useful for the treatment of a number of bacterial infections. It is a third-generation cephalosporin. As a class, cephalosporins have activity against Gram-positive and Gram-negative bacteria. The balance of activity tips toward Gram-positive organisms for earlier generations; later generations of cephalosporins have more Gram-negative coverage. Ceftazidime is one of the few in this class with activity against Pseudomonas. It is not active against methicillin-resistant Staphylococcus aureus. Third-generation cephalosporins differ from earlier generations in the presence of a C=N-OCH3 group in their chemical structure (Cefuroxime & Cefuzonam also bear this functional group but are only listed as class II). This group provides improved stability against certain beta-lactamase enzymes produced by Gram-negative bacteria. These bacterial enzymes rapidly destroy earlier-generation cephalosporins by breaking open the drug's beta-lactam chemical ring, leading to antibiotic resistance. Though initially active against these bacteria, with widespread use of third-generation cephalosporins, some Gram-negative bacteria known as extended-spectrum beta-lactamases (ESBLs) are even able to inactivate the third-generation cephalosporins. Infections caused by ESBL-producing Gram-negative bacteria are of particular concern in hospitals and other healthcare facilities. It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system.