Penem

A penem is a type of β-lactam with an unsaturated five-member heterocycle containing a sulfur atom in a pentacyclic ring fused to the β-lactam ring. Penems do not occur naturally; all are synthetic.^[1] Related to penems are carbapenems, which have a carbon atom in place of the sulfur atom.^[2]

An example is faropenem.^[3]

Structure

Faropenem, a penem. A sulfur atom and a double bond are present in the pentacyclic ring.

Imipenem, a carbapenem. Imipenem has a sulfur atom that is not in the pentacyclic ring.

Benzylpenicillin, a penicillin. The double bond is absent in the pentacyclic ring.

Penem molecules do not occur naturally, and production of penems is an entirely synthetic process.

Five main penem subgroups — thiopenems, oxypenems, aminopenems, alkylpenems, and arylpenems — have been produced and are distinguished by the side chain (at position 2) of the unsaturated five-membered ring. One structurally distinct penem is BRL 42715. This molecule has no substitution at the above position, but has a bulky group attached to the β-lactam ring, and it displays effective inhibition of class C β-lactamases, but no antimicrobial activity.

One possible consequence of these structural differences of penems from other β-lactams may be reduced immunogenicity and immunogenic cross-reactivity.

References

^ Richard Wise (1990). "The carbapenems and Penem Antibiotics—a brief review". Antimicrobic Newsletter. 7 (10): 73–78. doi:10.1016/0738-1751(90)90045-E.
^ "Medscape.com".
^ Milazzo I, Blandino G, Caccamo F, Musumeci R, Nicoletti G, Speciale A (March 2003). "Faropenem, a new oral penem: antibacterial activity against selected anaerobic and fastidious periodontal isolates". Journal of Antimicrobial Chemotherapy. 51 (3): 721–5. doi:10.1093/jac/dkg120. PMID 12615878.

β-lactamase sensitive (1st generation)	Benzylpenicillin (G)^# Benzathine benzylpenicillin^# Procaine benzylpenicillin^# Phenoxymethylpenicillin (V)^# Propicillin^‡ Pheneticillin^‡ Azidocillin^‡ Clometocillin^‡ Penamecillin^‡
β-lactamase resistant (2nd generation)	Cloxacillin^# (Dicloxacillin Flucloxacillin) Oxacillin Nafcillin Methicillin^‡

Extended
spectrum

Aminopenicillins (3rd generation)	Amoxicillin^# Ampicillin^# (Pivampicillin Hetacillin^‡ Bacampicillin^‡ Lenampicillin Metampicillin^‡ Talampicillin^‡) Epicillin^‡
Carboxypenicillins (4th generation)	Ticarcillin Carbenicillin^‡ / Carindacillin^‡ Temocillin^‡
Ureidopenicillins (4th generation)	Piperacillin Azlocillin^‡ Mezlocillin^‡
Other	Mecillinam (Pivmecillinam) Sulbenicillin^‡

Carbapenems / Penems

Cephems
Cephalosporins
Cephamycins
Carbacephems

1st generation	Cefazolin^# Cefalexin ^# Cefadroxil Cefapirin Cefazedone^‡ Cefazaflur^‡ Cefradine^‡ Cefroxadine^‡ Ceftezole^‡ Cefaloglycin^‡ Cefacetrile^‡ Cefalonium^‡ Cefaloridine^‡ Cefalotin Cefatrizine^‡
2nd generation	Cefaclor Cefprozil Cefuroxime Cefuroxime axetil Cefamandole^‡ Cefonicid^‡ Ceforanide^‡ Cefuzonam^‡ Cephamycin (Cefoxitin Cefotetan Cefminox^‡ Cefbuperazone^‡ Cefmetazole^‡) Carbacephem (Loracarbef^‡)
3rd generation	Cefixime^# Ceftriaxone^# Cefotaxime^# Antipseudomonal (Ceftazidime^# Cefoperazone) Cefdinir Cefcapene Cefdaloxime Ceftizoxime Cefmenoxime Cefpiramide Cefpodoxime Ceftibuten Cefditoren Cefotiam^‡ Cefetamet^‡ Cefodizime^‡ Cefpimizole^‡ Cefsulodin^‡ Cefteram^‡ Ceftiolene^‡ Oxacephem (Flomoxef Latamoxef^‡)
4th generation	Cefepime Cefozopran^‡ Cefpirome Cefquinome^‡
5th generation	Ceftaroline fosamil Ceftolozane Ceftobiprole
Siderophore	Cefiderocol^#
Veterinary	Ceftiofur Cefquinome Cefovecin

Monobactams

β-lactamase inhibitors

Combinations

Polypeptides

Glycopeptides Lipoglycopeptides	Inhibit PG chain elongation: Vancomycin^# (Oritavancin Telavancin) Teicoplanin (Dalbavancin) Ristocetin^‡ Avoparcin Inhibit autolysin: Corbomycin (not approved)
Lipopeptides	Insert into bacterial cell wall causing perforation and depolarization: Daptomycin Surfactin
Polymyxins	Bind to LPS in the outer bacterial membrane, acting in detergent-like fashion: Colistin Polymyxin B
Other	Inhibits PG elongation and crosslinking: Ramoplanin^§