|Bioavailability||30–37% (oral, fosfomycin tromethamine); varies with food intake|
|Biological half-life||5.7 hours (mean)|
|Excretion||Renal and fecal, unchanged|
|Chemical and physical data|
|Molar mass||138.059 g/mol|
|3D model (JSmol)|
|Melting point||94 °C (201 °F)|
Fosfomycin (also known as phosphomycin or phosphonomycin and the trade names Monurol and Monuril) is a broad-spectrum antibiotic produced by certain Streptomyces species, although it can now be made by chemical synthesis.
Fosfomycin (originally known as phosphonomycin) was discovered in a joint effort of Merck and Co. and Spain's Compañía Española de Penicilina y Antibióticos (CEPA). It was first isolated by screening broth cultures of Streptomyces fradiae isolated from soil samples for the ability to cause formation of spheroplasts by growing bacteria. The discovery was described in a series of papers published in 1969. CEPA began producing fosfomycin on an industrial scale in 1971 at its Aranjuez facility.
Fosfomycin is indicated in the treatment of urinary tract infections (UTIs), where it is usually administered as a single oral megadose. Its use in combination with tobramycin to treat lung infections in patients with cystic fibrosis was also explored.
The drug is well tolerated and has a low incidence of harmful side effects. However, development of bacterial resistance under therapy is a frequent occurrence and makes fosfomycin unsuitable for sustained therapy of severe infections. It is not recommended for children and those over 75 years old.
Mechanism of action
Fosfomycin is bactericidal and inhibits bacterial cell wall biogenesis by inactivating the enzyme UDP-N-acetylglucosamine-3-enolpyruvyltransferase, also known as MurA. This enzyme catalyzes the committed step in peptidoglycan biosynthesis, namely the ligation of phosphoenolpyruvate (PEP) to the 3'-hydroxyl group of UDP-N-acetylglucosamine. This pyruvate moiety provides the linker that bridges the glycan and peptide portion of peptidoglycan. Fosfomycin is a PEP analog that inhibits MurA by alkylating an active site cysteine residue (Cys 115 in the Escherichia coli enzyme).
Fosfomycin enters the bacterial cell through the glycerophosphate transporter.
Antibacterial spectrum and susceptibility
Fosfomycin has broad antibacterial activity against both Gram-positive and Gram-negative pathogens, with useful activity against E. faecalis, E. coli, and various Gram-negatives such as Citrobacter and Proteus. Given a greater activity in a low-pH milieu, and predominant excretion in active form into the urine, fosfomycin has found use for the prophylaxis and treatment of UTIs caused by these uropathogens. Of note, activity against S. saprophyticus, Klebsiella, and Enterobacter is variable and should be confirmed by minimum inhibitory concentration testing. Activity against extended-spectrum β-lactamase-producing pathogens, notably ESBL-producing E. coli, is good to excellent, because the drug is not affected by cross-resistance issues. Existing clinical data support use in uncomplicated UTIs, caused by susceptible organisms. However, susceptibility break-points of 64 mg/l should not be applied for systemic infections.
Biosynthetic gene cluster
The complete fosfomycin biosynthetic gene cluster from Streptomyces fradiae has been cloned and sequenced and the heterologous production of fosfomycin in S. lividans has been achieved by Ryan Woodyer of the Huimin Zhao and Wilfred van der Donk research groups.
Fosfomycin resistance enzymes
Three related fosfomycin resistance enzymes (named FosA, FosB, and FosX) are members of the glyoxalase superfamily. These enzymes function by nucleophilic attack on carbon 1 of fosfomycin, which opens the epoxide ring and renders the drug ineffective. The enzymes differ by the identity of the nucleophile used in the reaction: glutathione for FosA, bacillithiol for FosB, and water for FosX. In general, FosA and FosX enzymes are produced by Gram-negative bacteria, whereas FosB is produced by Gram-positive bacteria.
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