Fosfomycin

● Links

Drug Name

Fosfomycin is a bactericidal antibiotic produced by strains of Streptomyces (Jia et al., 2017), such as S. fradiae, S. viridochromogenes, and S. wedmorensis (Hendlin et al., 1969). It is a broad-spectrum antibiotic typically used to treat uncomplicated urinary tract infections caused by Escherichia coli (E. coli) and Enterococcus faecalis (E. faecalis). Although fosfomycin is a natural product, it is synthetically produced for commercial use.

The antibacterial drug, fosfomycin tromethamine, is a derivative of fosfomycin and is not chemically related to any other marketed antibacterial agent (Michalopoulos et al., 2011); therefore, it does not belong to a specific drug class. The drug is available as a tromethamine or calcium salt to be taken orally; however, fosfomycin tromethamine is preferred over the calcium salt of fosfomycin, because of its superior oral bioavailability (Frimodt-Møller, 2010). After absorption, fosfomycin—trometamol releases fosfomycin by hydrolysis (Raz, 2012).

Table 1. Basic profile of fosfomycin

Description Oral, synthetically produced broad-spectrum antibacterial drug
Target(s) UDP-N-acetylglucosamine enolpyruvyl transferase (MurA); MurA is also known as MurZ in E. coli
Generic Fosfomycin Tromethamine (synonym: Fosfomycin Trometamol)
Commercial Name Monurol (United States, Canada)
Combination Drug(s) N/A
Other Synonyms Phosphomycin, Phosphonomycin, Phosphonemycin, Fosfomycinum, Fosfomycine, FCM
IUPAC Name [(2R,3S)-3-methyloxiran-2-yl] phosphonic acid
Ligand Code in PDB FFQ (bound to target protein); FCN (unbound)
PDB structure 3kr6 (fosfomycin bound to target protein MurA)
ATC code J01XX01
RotateHydrogensLabels
Figure 1. 2D and 3D structures of Fosfomycin (PDB ligand code: FCN).

Antibiotic Chemistry

Fosfomycin is a phosphonic acid derivative and has three key groups in the molecule (Figure 2). The epoxide group is critical to its function as an antibiotic (Castañeda-García, et al., 2013).

Figure 2. 2D structure of fosfomycin showing the functional moieties responsible for antibacterial activity. The structure was drawn using ChemAxon.
Figure 2. 2D structure of fosfomycin showing the functional moieties responsible for antibacterial activity. The structure was drawn using ChemAxon.

Drug Information

Table 2. Chemical and physical properties (DrugBank).

Chemical Formula C3H7O4P
Molecular Weight 138.06 g/mol
Calculated Predicted Partition Coefficient: cLogP -1.6
Calculated Predicted Aqueous Solubility: cLogS -0.47
Solubility (in water) 46.9 mg/mL
Predicted Topological Polar Surface Area (TPSA) 70 Å2

Drug Target

Fosfomycin is an oral, broad-spectrum antibacterial drug that inhibits the enzyme UDP-N-acetylglucosamine enolpyruvyl transferase (MurA). MurA is responsible for the first committed cytoplasmic step of peptidoglycan biosynthesis and initiates the production of the peptidoglycan precursor (Silver, 2017). The enzyme, as the name suggests, catalyzes the transfer of enolpyruvate from phosphoenolpyruvate (PEP) to uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc), which yields enolpyruvyl UDP-GlcNAc (Hrast et al., 2014). This reaction is required to initiate the formation of the nucleotide muramyl peptides which will serve as precursors to the cell-wall building blocks (Hendlin et al., 1969). Click here to learn more about MurA.

In E. coli, fosfomycin reaches its intracellular target via two uptake systems: the hexose-6-phosphate transport system (because fosfomycin is a molecular mimic of glucose-6-phosphate, or G6P) and the L-alpha-glycerophosphate transport system (because fosfomycin is also a molecular mimic of glycerol-3-phosphate, or G3P), as illustrated in Figure 3 (Frimodt-Møller, 2010).

After entering the cell, fosfomycin is recognized by MurA and binds to the enzyme active site, where the formation of a covalent adduct occurs in the drug-target complex. Irreversible inhibition of MurA by fosfomycin blocks bacterial cell wall biosynthesis causing cell lysis and death (Dijkmans et al., 2017).

Figure 3. Cartoon showing how fosfomycin enters the bacterial cell using the two possible uptake systems and then binds to its intracellular target, MurA. Portions of the figure were adapted from Servier Medical Art. Source: adapted from (Dijkmans et al., 2017).
Figure 3. Cartoon showing how fosfomycin enters the bacterial cell using the two possible uptake systems and then binds to its intracellular target, MurA. Portions of the figure were adapted from Servier Medical Art. Source: adapted from (Dijkmans et al., 2017).

Drug-Target Complex

The target of fosfomycin, MurA, is a 419 amino acid protein, consisting of two closely approximated globular domains (Skarzynski et al., 1996, Figure 4):
* Catalytic domain (residues 22-229, blue)
* C-terminal domain (residues 1-21 and 230-419, green)

The active site is located between the two domains (Skarzynski et al., 1996), where UDP-GlcNAc (gray stick figure) and fosfomycin (white ball-and-stick figure) bind (Figure 4).

In the absence of fosfomycin, MurA is thought to catalyze the transfer of enolpyruvate from PEP to UDP-GlcNAc, yielding enolpyruvyl UDP-GlcNAc in a multi-step process. First, UDP-GlcNAc binds to MurA, inducing a significant conformational change in the structure of the protein. Thereafter, PEP binds to a second subsite within the enzyme active site, allowing the transfer reaction to proceed.

Fosfomycin, a PEP analogue, can also bind to the PEP-binding site of MurA (presumably after binding of UDP-GlcNAc) and functions by alkylating the catalytic cysteine residue (Cys115 in E.coli and E. cloacae) (Bensen et al., 2012). When the antibiotic binds, the enzyme catalyzes a single turnover reaction resulting in the formation of a covalent adduct with Cys115. This covalent modification step irreversibly inactivates the enzyme (Hendlin et al., 1969), by preventing binding of PEP. The covalent interaction between fosfomycin and the catalytic residue is shown in Figure 4.

Figure 4. Ribbon representation of the structure of MurA bound to UDP-GlcNAc (color-coded atomic stick figure: C-gray, N-blue, O-red, P-orange) and fosfomycin (color-coded atomic ball-and-stick figure: C-white, O-red, P-orange). The inset shows the covalent adduct (depicted in yellow) that forms between fosfomycin and Cys115 (color-coded ball-and-stick figure: C-pink, S-yellow) (PDB ID: 3kr6; Han et al., 2010).
Figure 4. Ribbon representation of the structure of MurA bound to UDP-GlcNAc (color-coded atomic stick figure: C-gray, N-blue, O-red, P-orange) and fosfomycin (color-coded atomic ball-and-stick figure: C-white, O-red, P-orange). The inset shows the covalent adduct (depicted in yellow) that forms between fosfomycin and Cys115 (color-coded ball-and-stick figure: C-pink, S-yellow) (PDB ID: 3kr6; Han et al., 2010).

As illustrated in Figure 4, fosfomycin is tightly packed between UDP-GlcNAc and the enzyme (Skarzynski et al., 1996). Three active-site residues (Lys22, Arg120, and Arg397) surround the phosphonate group of fosfomycin. These positively charged residues both neutralize and make a total of five hydrogen bonds with the phosphonate group (Figure 5a). Similar interactions enable recognition of the phosphate group of the substrate PEP, as shown in Figure 5b (Zhu et al., 2012).

Figure 5. (a) Hydrogen bonding interactions (magenta lines) between fosfomycin (atom color coding as in Figure 4) and the active site of MurA (PDB ID: 3kr6; Han et al., 2010). (b) Hydrogen bonding interactions (magenta lines) between PEP (color-coded atomic ball-and-stick figure: C-white, O-red, P-orange) and MurA (PDB ID: 3swd; Zhu et al., 2012).
Figure 5. (a) Hydrogen bonding interactions (magenta lines) between fosfomycin (atom color coding as in Figure 4) and the active site of MurA (PDB ID: 3kr6; Han et al., 2010). (b) Hydrogen bonding interactions (magenta lines) between PEP (color-coded atomic ball-and-stick figure: C-white, O-red, P-orange) and MurA (PDB ID: 3swd; Zhu et al., 2012).

A comparison of the co-crystal structures of MurA with fosfomycin (Figure 5a) and of MurA with PEP (Figure 5b) shows that fosfomycin acts by occluding the PEP binding site and preventing substrate binding (Skarzynski et al., 1996).

It was found that fosfomycin is able to carry out time-dependent inactivation of MurA more rapidly in the presence of UDP-GlcNAc (Zoeiby et al., 2003). This suggests that the conformational changes that UDP-GlcNAc binding induces in the active site are essential for inhibition of MurA by fosfomycin (Zoeiby et al., 2003).

Pharmacologic Properties and Safety

Table 3. Pharmacokinetics: ADMET of fosfomycin.

Features Comment(s) Source
Oral Bioavailability (%) 37% DrugBank
IC50 (µM) 8.8 µM (Baum et al., 2001)
Ki (µM) N/A N/A
Half-life (hrs) 5.7 (± 2.8) hours DrugBank
Duration of Action 6-8 hours FDA
Absorption Site Small intestine (Dijkmans et al., 2017)
Transporter(s) GlpT and UhpT, in E. coli (Dijkmans et al., 2017)
Metabolism No transformation, excreted unchanged DrugBank
Excretion Excreted unchanged in both urine and feces: ~ 38% recovered from urine; ~18% recovered from feces FDA
AMES Test (Carcinogenic Effect) Probability 0.6575 (Non AMES toxic) DrugBank
hERG Safety Test (Cardiac Effect) Probability 0.9456 (weak inhibitor) DrugBank
Liver Toxicity Liver injury due to fosfomycin is rare. A single case report regarding a young man who developed acute hepatitis after receiving a single, large oral dose of fosfomycin has been published. LiverTox

Drug Interactions and Side Effects

Table 4. Drug interactions and side effects of fosfomycin.

Features Comment(s) Source
Total Number of Drug Interactions 3 drugs Drugs.com
Major Drug Interaction(s) cholera vaccine, live Drugs.com
Alcohol/Food Interaction(s) N/A N/A
Disease Interaction(s) Hemodialysis (moderate) Renal dysfunction (moderate) Drugs.com
On-target Side Effects diarrhea, nausea, abdominal pain, stomach ache, vaginitis Drugs.com
Off-target Side Effects headache, dizziness, anaphylactic shock (very rare), rhinitis (stuffy nose) Drugs.com
CYP Interactions None Drugs.com

Regulatory Approvals/Commercial

The US FDA approved monurol (fosfomycin), as an oral antibacterial drug, in 1996. The drug is largely used for the treatment of uncomplicated urinary tract infections (acute cystitis) (Sastry et al., 2015).

Monurol is available as a single three-gram oral dose contained within a sachet. The contents of the sachet (white granules) must be dissolved in water before being consumed. Only one three-gram dose of monurol should be used to treat a single occurrence of acute cystitis.

In clinical trials, the most frequently reported side effects (>1%) in the study population included diarrhea, headache, vaginitis (vaginal inflammation), nausea, rhinitis (stuffy nose), and back pain. Other rarer side effects (<1%) included abnormal stools, anorexia, constipation, dry mouth, ear disorder, migraine, and vomiting. One patient developed unilateral optic neuritis, the occurrence of which is possibly related to treatment by monurol (FDA).

Off-Target Considerations

The US FDA approved antibacterial drug fosfomycin not only inhibits the bacterial enzyme MurA but also plays a role in the modulation of the host immune system (Falagas et al., 2016). Fosfomycin enhances the ability of neutrophils to phagocytically kill invading pathogens, and it was seen that neutrophils have an enhanced bactericidal ability in the presence of fosfomycin compared to other antimicrobial agents (Falagas et al., 2016).

Links

Table 5. Links to learn more about fosfomycin

Comprehensive Antibiotic Resistance Database (CARD) ARO: 0000025
DrugBank DB00828
Drugs.com https://www.drugs.com/mtm/fosfomycin.html
FDA https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/050717s005lbl.pdf
LiverTox: National Institutes of Health (NIH) https://www.ncbi.nlm.nih.gov/books/NBK547912/
PubChem CID 446987

Learn about Fosfomycin Resistance.

References

Baum, E. Z., Montenegro, D. A., Licata, L., Turchi, I., Webb, G. C., Foleno, B. D., Bush, K. (2001) Identification and Characterization of New Inhibitors of the Escherichia coli MurA Enzyme. Antimicrobial Agents and Chemotherapy 45, 3182-3188. https://doi.org/10.1128/aac.45.11.3182-3188.2001

Bensen, D. C., Rodriguez, S., Nix, J., Cunningham, M. L., Tari, L. W. (2012) Structure of MurA (UDP-N-acetylglucosamine enolpyruvyl transferase) from Vibrio fischeri in complex with substrate UDP-N-acetylglucosamine and the drug fosfomycin. Acta Crystallographica Section F: Structural Biology and Crystallization Communications 68, 382–385. https://doi.org/10.1107/s1744309112006720

Castañeda-García, A., Blázquez, J., Rodríguez-Rojas, A. (2013) Molecular Mechanisms and Clinical Impact of Acquired and Intrinsic Fosfomycin Resistance. Antibiotics (Basel). 2, 217-36. https://doi.org/10.3390/antibiotics2020217

Dijkmans, A. C., Zacarías, N. V., Burggraaf, J., Mouton, J. W., Wilms, E., Nieuwkoop, C. V., Touw, D. J., Stevens, J., Kamerling, I. M. (2017) Fosfomycin: Pharmacological, Clinical and Future Perspectives. Antibiotics 6, 24. https://doi.org/10.3390/antibiotics6040024

Falagas, M. E., Vouloumanou, E. K., Samonis, G., Vardakas, K. Z. (2016) Fosfomycin. Clinical Microbiology Reviews 29, 321-347. https://doi.org/10.1128/cmr.00068-15

Fosfomycin - DrugBank. Drugbank.ca. https://www.drugbank.ca/drugs/DB00828

Fosfomycin. Drugs.com. https://www.drugs.com/mtm/fosfomycin.html

Fosfomycin. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/fosfomycin

Frimodt-Møller, N. (2010) Fosfomycin. Kucers' The Use of Antibiotics Sixth Edition 935-944. https://doi.org/10.1201/b13787

Han, H., Yang, Y., Olesen, S. H., Becker, A., Betzi, S., Schönbrunn, E. (2010) The Fungal Product Terreic Acid Is a Covalent Inhibitor of the Bacterial Cell Wall Biosynthetic Enzyme UDP-N-Acetylglucosamine 1-Carboxyvinyltransferase (MurA). Biochemistry 49, 4276-4282. https://doi.org/10.1021/bi100365b PDB ID: 3kr6

Hendlin, D., Stapley, E. O., Jackson, M., Wallick, H., Miller, A. K., Wolf, F. J., Miller, T. W., Chaiet, L., Kahan, F. M., Foltz, E. L., Woodruff, H. B., Mata, J. M., Hernandez, S., Mochales, S. (1969) Phosphonomycin, a New Antibiotic Produced by Strains of Streptomyces. Science 166, 122-123. https://doi.org/10.1126/science.166.3901.122

Hrast, M., Sosič, I., Šink, R., Gobec, S. (2014) Inhibitors of the peptidoglycan biosynthesis enzymes MurA-F. Bioorganic Chemistry 55, 2-15. https://doi.org/10.1016/j.bioorg.2014.03.008

Jia, B., Raphenya, A. R., Alcock, B., Waglechner, N., Guo, P., Tsang, K. K., Lago, B. A., Dave, B. M., Pereira, S., Sharma, A. N., Doshi, S., Courtot, M., Lo, R., Williams, L. E., Frye, J. G., Elsayegh, T., Sardar, D. Westman, E. L., Pawlowski, A. C., Johnson, T. A., Brinkman, F. S., Wright, G. D., McArthur, A. G. (2017) CARD 2017: expansion and model-centric curation of the Comprehensive Antibiotic Resistance Database. Nucleic Acids Research 45, D566-573. https://doi.org/10.1093/nar/gkw1004

Michalopoulos, A. S., Livaditis, I. G., Gougoutas, V. (2011) The revival of fosfomycin. International Journal of Infectious Diseases 15, e732-e739. https://doi.org/10.1016/j.ijid.2011.07.007

Monurol. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/050717s005lbl.pdf

Raz, R. (2012) Fosfomycin: An old—new antibiotic. Clinical Microbiology and Infection 18 , 4-7. https://doi.org/10.1111/j.1469-0691.2011.03636.x

Sastry, S., Clarke, L. G., Alrowais, H., Querry, A. M., Shutt, K. A., Doi, Y. (2015) Clinical Appraisal of Fosfomycin in the Era of Antimicrobial Resistance. Antimicrobial Agents and Chemotherapy 59, 7355-7361. https://doi.org/10.1128/aac.01071-15

Silver, L. L. (2017) Fosfomycin: Mechanism and Resistance. Cold Spring Harbor Perspectives in Medicine 7. https://doi.org/10.1101/cshperspect.a025262

Skarzynski, T., Mistry, A., Wonacott, A., Hutchinson, S. E., Kelly, V. A., Duncan, K. (1996) Structure of UDP-N-acetylglucosamine enolpyruvyl transferase, an enzyme essential for the synthesis of bacterial peptidoglycan, complexed with substrate UDP-N-acetylglucosamine and the drug fosfomycin. Structure 4, 1465-1474. https://doi.org/10.1016/S0969-2126(96)00153-0

Zhu, J., Yang, Y., Han, H., Betzi, S., Olesen, S. H., Marsilio, F., Schönbrunn, E. (2012) Functional Consequence of Covalent Reaction of Phosphoenolpyruvate with UDP-N-acetylglucosamine 1-Carboxyvinyltransferase (MurA). Journal of Biological Chemistry 287, 12657-12667. https://doi.org/10.1074/jbc.m112.342725 PDB ID: 3swd

March 2025, Gauri Patel, Helen Gao, and Shuchismita Dutta; Reviewed by Dr. Lynn Silver
https://doi.org/10.2210/rcsb_pdb/GH/AMR/drugs/antibiotics/cellwall-biosynth/mura/phosphonate-antibiotic/fosfomycin