The<unk>  nucleus can be modified to gain different properties.<unk> s are sometimes grouped into "generations" by their antimicrobial properties. The first<unk> s were designated first-generation<unk> s, whereas, later, more extended-spectrum<unk> s were classified as second-generation<unk> s. Each newer generation has significantly greater Gram-negative antimicrobial properties than the preceding generation, in most cases with decreased activity against Gram-positive organisms. Fourth-generation<unk> s, however, have true broad-spectrum activity. The classification of<unk> s into "generations" is commonly practised, although the exact categorization is often imprecise. For example, the fourth generation of<unk> s is not recognized as such in Japan. In Japan, cefaclor is classed as a first-generation<unk> , though in the United States it is a second-generation one; and cefbuperazone, cefminox, and cefotetan are classed as second-generation<unk> s. Third Generation Cefmetazole and cefoxitin are classed as third-generation<unk> ems. Flomoxef and latamoxef are in a new class called oxacephems. Fourth Generation Fourth-generation<unk> s as of March, 2007, were considered to be "a class of highly potent antibiotics that are among medicine's last defenses against several serious human infections" according to The Washington Post. Further Generations Some state that<unk> s can be divided into five or even six generations, although the usefulness of this organization system is of limited clinical relevance. Naming Most first-generation<unk> s were originally spelled "ceph-" in English-speaking countries. This continues to be the preferred spelling in the United States, Australia, and New Zealand, while European countries (including the United Kingdom) have adopted the International Nonproprietary Names, which are always spelled "cef-". Newer first-generation<unk> s and all<unk> s of later generations are spelled "cef-", even in the United States. Activity The mnemonic "LAME" is used to note organisms against which<unk> s do not have activity: *Listeria *Atypicals (including Mycoplasma and Chlamydia) *MRSA *Enterococci Fifth-generation<unk> s, however, are effective against MRSA. Overview table Name Description Common Alternate name or spelling Brand (#) = noncephalosporins similar to generation # H, human; V, veterinary; W, withdrawn; P, Pseudomonas; MR, methicillin-resistant Staphylococcus aureus; An, anaerobe 1 Cefalexin<unk> alexin Keflex H V Gram-positive: Activity against penicillinase-producing, methicillin-susceptible staphylococci and streptococci (though they are not the drugs of choice for such infections). No activity against methicillin-resistant staphylococci or enterococci. Gram-negative: Activity against Proteus mirabilis, some Escherichia coli, and Klebsiella pneumoniae ("PEcK"), but have no activity against Bacteroides fragilis, Pseudomonas, Acinetobacter, Enterobacter, indole-positive Proteus, or Serratia. Cefadroxil cefadroxyl Duricef H Cefazolin<unk> azolin Ancef, Kefzol H Cefapirin<unk> apirin Cefadryl V Cefacetrile<unk> acetrile Cefaloglycin<unk> aloglycin Cefalonium<unk> alonium Cefaloridine<unk> aloradine Cefalotin<unk> alothin Keflin Cefatrizine Cefazaflur Cefazedone Cefradine<unk> radine Velosef Cefroxadine Ceftezole 2 Cefuroxime Altacef, Zefu, Zinnat, Zinacef, Ceftin, Biofuroksym, Xorimax H Gram-positive: Less than first-generation. Gram-negative: Greater than first-generation: HEN Haemophilus influenzae, Enterobacter aerogenes and some Neisseria + the PEcK described above. Cefprozil cefproxil Cefzil H Cefaclor Ceclor, Distaclor, Keflor, Raniclor H Cefonicid Monocid Cefuzonam (2) Cefoxitin Mefoxin H An<unk> amycins sometimes grouped with second-generation<unk> s Cefotetan Cefotan H An Cefmetazole Zefazone An Cefminox Cefbuperazone Cefotiam Pansporin Loracarbef Lorabid The carbacephem analog of cefaclor 3 Cefdinir Sefdin, Zinir, Omnicef, Kefnir H Gram-positive: Some members of this group (in particular, those available in an oral formulation, and those with antipseudomonal activity) have decreased activity against gram-positive organisms. Activity against staphylococci and streptococci is less with the third-generation compounds than with the first- and second-generation compounds. Gram-negative: Third-generation<unk> s have a broad spectrum of activity and further increased activity against gram-negative organisms. They may be particularly useful in treating hospital-acquired infections, although increasing levels of extended-spectrum beta-lactamases are reducing the clinical utility of this class of antibiotics. They are also able to penetrate the central nervous system, making them useful against meningitis caused by pneumococci, meningococci, H. influenzae, and susceptible E. coli, Klebsiella, and penicillin-resistant N. gonorrhoeae. Since August 2012, the third-generation<unk> , ceftriaxone, is the only recommended treatment for gonorrhea in the United States (in addition to azithromycin or doxycycline for concurrent Chlamydia treatment). Cefixime is no longer recommended as a first-line treatment due to evidence of decreasing susceptibility. Ceftriaxone Rocephin H Ceftazidime Meezat, Fortum, Fortaz H P Cefixime Fixx, Zifi, Suprax H Cefpodoxime Vantin, PECEF, Simplicef H V Ceftiofur Naxcel, Excenel H V Cefotaxime Claforan H Ceftizoxime Cefizox H Cefditoren H Ceftibuten Cedax H Cefovecin Convenia V Cefdaloxime Cefcapene Cefetamet Cefmenoxime Cefodizime Cefpimizole Cefteram Ceftiolene Cefoperazone Cefobid W P (3) Latamoxef moxalactam W An oxacephem sometimes grouped with third-generation<unk> s 4 Cefepime Maxipime H P Gram-positive: They are extended-spectrum agents with similar activity against Gram-positive organisms as first-generation<unk> s. Gram-negative: Fourth-generation<unk> s are zwitterions that can penetrate the outer membrane of Gram-negative bacteria. They also have a greater resistance to β-lactamases than the third-generation<unk> s. Many can cross the blood–brain barrier and are effective in meningitis. They are also used against Pseudomonas aeruginosa. Cefiderocol has been called a fourth-generation<unk>  by only one source as of November 2019. Cefiderocol Fetroja H Cefquinome V Cefclidine Cefluprenam Cefoselis Cefozopran Cefpirome Cefrom (4) Flomoxef An oxacephem sometimes grouped with fourth-generation<unk> s 5 Ceftaroline H MR Ceftobiprole has been described as "fifth-generation"<unk> , though acceptance for this terminology is not universal. Ceftobiprole has anti-pseudomonal activity and appears to be less susceptible to development of resistance. Ceftaroline has also been described as "fifth-generation"<unk> , but does not have the activity against Pseudomonas aeruginosa or vancomycin-resistant enterococci that ceftobiprole has. Ceftolozane is an option for the treatment of complicated intra-abdominal infections and complicated urinary tract infections. It is combined with the β-lactamase inhibitor tazobactam, as multi-drug resistant bacterial infections will generally show resistance to all β-lactam antibiotics unless this enzyme is inhibited. Ceftolozane H Ceftobiprole MR ? Cefaloram These<unk> ems have progressed far enough to be named, but have not been assigned to a particular generation. Nitrocefin is a chromogenic<unk>  substrate, and is used for detection of β-lactamases. Cefaparole Cefcanel Cefedrolor Cefempidone Cefetrizole Cefivitril Cefmatilen Cefmepidium Cefoxazole Cefrotil Cefsumide Ceftioxide Cefuracetime Nitrocefin
Cephalosporin
Sulfonamide 
Extended-spectrum penicillin
Quinolone antibiotic
Tetracycline
Minocycline
Anthopleurin
Penicillin