Moxifloxacin

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Drug Name

Moxifloxacin is a synthetic antibiotic that is a member of the fluoroquinolone class. It inhibits DNA synthesis in susceptible bacteria by binding to DNA gyrase and topoisomerase IV and stabilizing a cleaved-DNA complex. Moxifloxacin is a broad-spectrum drug that exhibits activity against gram-positive and gram-negative bacteria (DrugBank).

Table 1. Basic profile of moxifloxacin.

Description Broad-spectrum fluoroquinolone antibiotic
Target(s) DNA gyrase, topoisomerase IV
Generic Moxifloxacin
Commercial Name Avelox (tablet; solution for IV use), Moxeza (ophthalmic solution); Vigamox (ophthalmic solution)
Combination Drug(s) N/A
Other Synonyms N/A
IUPAC Name 7-[(4aS,7aS)-octahydro-1H-pyrrolo[3,4-b]pyridin-6-yl]-1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid
Ligand Code in PDB MFX
PDB Structure 2xkk (Structure of Moxifloxacin Bound to Topoisomerase IV)
ATC code J01MA14
RotateHydrogensLabels
Figure 1. 2D and 3D structures of Moxifloxacin (PDB ligand code: MFX).

Antibiotic Chemistry

The unique structural features of moxifloxacin allow it to bind to the 30S subunit and provide the drug with potency against a wide variety of bacterial species. Moxifloxacin is a semisynthetic fluoroquinolone with a diazabicyclononyl ring and a methoxy group.

Figure 2. Chemical structure of moxifloxacin. Key chemical groups are colored and labeled. Structure created using ChemDraw.
Figure 2. Chemical structure of moxifloxacin. Key chemical groups are colored and labeled. Structure created using ChemDraw.

Drug Information

Table 2. Chemical and physical properties (DrugBank).

Chemical Formula C21H24FN3O4
Molecular Weight 401.43 g/mol
Calculated Predicted Partition Coefficient: cLogP 0.01
Calculated Predicted Aqueous Solubility: cLogS -3.4
Solubility (in water) 0.168 mg/mL
Predicted Topological Polar Surface Area (TPSA) 82.11 Å2

Drug Target

Moxifloxacin targets type IIA topoisomerase - DNA gyrase and topoisomerase IV. These enzymes are ATP-dependent and modify DNA topology during replication. They act by creating a double-stranded break in one segment of DNA and passing a second intact segment through it. Moxifloxacin binds to these enzymes and prevents them from ligating DNA, creating the potential for the cell to generate double-stranded breaks. The accumulation of cleaved DNA prevents DNA replication and transcription, quickly leading to cell death (Schoeffler et al., 2008).

Learn more about DNA synthesis or replication.

Learn more about the type IIA topoisomerases.

Drug-Target Complex

The rest of this description will focus specifically on the binding of moxifloxacin to topoisomerase IV. The enzyme is a tetramer containing two ParC subunits (colored in shades of blue in Figure 3) and two ParE subunits (colored in shades of orange in Figure 3).

Two moxifloxacin molecules bind near the active site—one at each DNA break—and prevent the DNA from being ligated. They sterically block each end of the DNA break from coming together and reforming their phosphodiester bond. The drugs wedge themselves between the two ends of the cleaved DNA strands and make direct contact with the DNA, a Mg2+ ion, and water molecules. The contacts with DNA are largely through π-π stacking and van der Waals interactions (Wohlkonig et al., 2010). Contacts with the Mg2+ ion and water molecules are crucial because they mediate the binding of the drug to the enzyme. Two oxygen atoms from the keto-acid group of the drugs interact with the Mg2+ ion and water molecules. The Mg2+ ion in turn interacts with four water molecules which are coordinated via hydrogen bonds by a serine and a glutamic acid residue. This coordination sphere serves to tether the drug to the enzyme (Wohlkonig et al., 2010). Figure 3 shows the interactions in the binding site of moxifloxacin. It is important to note that the Mg2+ ions the drugs interact with are separate from the catalytic ions in the active site.

Figure 3. The left image shows a ribbon representation of topoisomerase IV. The DNA is colored in purple. The inset shows the interactions that moxifloxacin makes with topoisomerase IV. Hydrogen bonds are shown in pink and non-hydrogen bond interactions with the Mg2+ ion are shown with purple dashed lines (PDB ID: 2xkk, Wohlkonig et al., 2010).
Figure 3. The left image shows a ribbon representation of topoisomerase IV. The DNA is colored in purple. The inset shows the interactions that moxifloxacin makes with topoisomerase IV. Hydrogen bonds are shown in pink and non-hydrogen bond interactions with the Mg2+ ion are shown with purple dashed lines (PDB ID: 2xkk, Wohlkonig et al., 2010).

The binding of two moxifloxacin molecules stabilizes the “cleavage complex” between the enzyme and DNA by preventing the 3’ hydroxyl in the DNA from attacking the 5’ phosphate. The drugs do so by increasing the distance between the two groups by 2.5 Å. As a result, the reformation of the phosphodiester bond in the DNA backbone is prevented. If the enzyme-DNA complex is ruptured, it will form a double-stranded break leading to cell death (Laponogov et al., 2009).

Figure 4. Comparison of the active sites in topoisomerase IV showing a DNA break - a) without any drug molecules - the 3’-OH group, 5’-phosphate group, and catalytic tyrosine residues are labeled (PDB ID: 3ksa, Laponogov et al., 2010); and b) in the presence of moxifloxacin (MFX). The same residues from Figure 4a are labeled (PDB ID: 3fof, Laponogov et al., 2009).
Figure 4. Comparison of the active sites in topoisomerase IV showing a DNA break - a) without any drug molecules - the 3’-OH group, 5’-phosphate group, and catalytic tyrosine residues are labeled (PDB ID: 3ksa, Laponogov et al., 2010); and b) in the presence of moxifloxacin (MFX). The same residues from Figure 4a are labeled (PDB ID: 3fof, Laponogov et al., 2009).

Pharmacologic Properties and Safety

Table 3. Pharmacokinetics: ADMET of moxifloxacin.

Features Comment(s) Source
Oral Bioavailability (%) ≈ 90% DrugBank
IC50 (μM) 10 μM (for binding to DNA gyrase in S. pneumoniae); 2.5 μM (for binding to topoisomerase IV in S. pneumoniae); 1.6 μM (for binding to DNA gyrase in E. coli); 20 μM (for binding to topoisomerase IV in E. coli) (Cambau et al., 2009)
Ki (μM) N/A N/A
Half-life (hrs) 11.5-15.6 hours (single dose, oral) DrugBank
Duration of Action 1-3 hours FDA
Absorption Site Gastrointestinal tract FDA
Transporter(s) N/A N/A
Metabolism ≈ 52% of the oral or IV dose is metabolized via glucuronide and sulphate conjugation DrugBank
Excretion ≈ 45% of the oral or IV dose is excreted unchanged (20% in urine and 25% in feces) DrugBank
AMES Test (Carcinogenic Effect) Probability 0.6227 (non-AMES toxic) FDA
hERG Safety Test (Cardiac Effect) Probability 0.8092 (weak-inhibitor) DrugBank
Liver Toxicity Associated with a low rate (1%-3%) of serum enzyme elevations; linked to rare but occasionally severe and fatal cases of acute liver injury LiverTox

Drug Interactions and Side Effects

Table 4. Drug interactions and side effects of moxifloxacin.

Features Comment(s) Source
Total Number of Drug Interactions 420 drug interactions Drugs.com
Major Drug Interaction(s) 211 major drug interactions (ex: azithromycin, prednisolone, warfarin) Drugs.com
Alcohol/Food Interaction(s) 1 interaction with multivitamins with minerals Drugs.com
Disease Interaction(s) 9 interactions (ex: colitis, liver disease, tendonitis) Drugs.com
On-Target Side Effects Nausea, diarrhea, headache, vomiting, and dizziness Drugs.com
Off-Target Side Effects N/A N/A
CYP Interactions None DrugBank

Cases of Clostridium difficile associated diarrhea (CDAD) have been reported with the use of almost all antibacterial drugs, including moxifloxacin, and may vary in severity from mild diarrhea to fatal colitis. CDAD occurs because treatment with antibiotics changes the normal bacterial flora of the colon, which results in an overgrowth of C. difficile (FDA, 2017).

Regulatory Approvals/Commercial

Moxifloxacin was first approved by the U.S. Food and Drug Administration in December 1999 for use against bacterial sinusitis, chronic bronchitis, and community-acquired pneumonia. Sold under the brand name AVELOX by Bayer, it was later approved to be used against complicated skin and intra-abdominal infections. Moxifloxacin is also manufactured as MOXEZA by Alcon to treat eye infections.

The FDA has issued numerous drug safety communication warnings regarding the fluoroquinolones. The use of fluoroquinolones is associated with tears in the aorta, significant decreases in blood sugar, tendinitis, and disabling side effects in muscles and nerves. Although the risks appear to be rare, the FDA recommends that the use of fluoroquinolones be restricted to only life-threatening bacterial infections.

Links

Table 5: Links to learn more about moxifloxacin

Comprehensive Antibiotic Resistance Database (CARD) ARO: 0000074
DrugBank DB00218
Drugs.com https://www.drugs.com/mtm/moxifloxacin.html
FDA Avelox: https://www.accessdata.fda.gov/drugsatfda_docs/label/2016/021085s063lbl.pdf Moxeza: https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/022428s002lbl.pdf
LiverTox: National Institutes of Health (NIH) https://www.ncbi.nlm.nih.gov/books/NBK548166/
PubChem ID 152946

Learn about moxifloxacin resistance.

References

Blower, T. R., Williamson, B. H., Kerns, R. J., Berger, J. M. (2016). Crystal structure and stability of gyrase-fluoroquinolone cleaved complexes from Mycobacterium tuberculosis. Proceedings of the National Academy of Sciences of the United States of America, 113(7), 1706–1713. https://doi.org/10.1073/pnas.1525047113

Cambau, E., Matrat, S., Pan, X., Roth Dit Bettoni, R., Corbel, C., Aubry, A., Lascols, C., Driot, J., Fisher, L. (2009). Target specificity of the new fluoroquinolone besifloxacin in Streptococcus pneumoniae, Staphylococcus aureus and Escherichia coli. Journal of Antimicrobial Chemotherapy, 63(3), pp.443-450. https://doi.org/10.1093/jac/dkn528

Fukuda, H., Hiramatsu, K. (1999). Primary targets of fluoroquinolones in Streptococcus pneumoniae. Antimicrobial agents and chemotherapy, 43(2), 410–412. https://doi.org/10.1128/aac.43.2.410

Khan, T., Sankhe, K., Suvarna, V., Sherje, A., Patel, K., Dravyakar, B. (2018). DNA gyrase inhibitors: Progress and synthesis of potent compounds as antibacterial agents. Biomedicine & Pharmacotherapy, 103, pp.923-938. https://doi.org/10.1016/j.biopha.2018.04.021

Laponogov, I., Pan, X. S., Veselkov, D. A., McAuley, K. E., Fisher, L. M., Sanderson, M. R. (2010). Structural basis of gate-DNA breakage and resealing by type II topoisomerases. PloS one, 5(6), e11338. https://doi.org/10.1371/journal.pone.0011338 PDB ID: 3ksb, 3ksa

Laponogov, I., Sohi, M., Veselkov, D., Pan, X., Sawhney, R., Thompson, A., McAuley, K., Fisher, L., Sanderson, M. (2009). Structural insight into the quinolone–DNA cleavage complex of type IIA topoisomerases. Nature Structural & Molecular Biology, 16(6), pp.667-669. https://doi.org/10.1038/nsmb.1604 PDB ID: 3fof

LiverTox - Clinical and Research Information on Drug-Induced Liver Injury. National Institutes of Health. https://www.ncbi.nlm.nih.gov/books/NBK548166/

Miller D. (2008). Review of moxifloxacin hydrochloride ophthalmic solution in the treatment of bacterial eye infections. Clinical ophthalmology (Auckland, N.Z.), 2(1), 77–91. https://doi.org/10.2147/opth.s1666

Moxifloxacin – DrugBank. Drugbank.ca. https://www.drugbank.ca/drugs/DB00218

Moxifloxacin. Drugs.com. https://www.drugs.com/mtm/moxifloxacin.html

Moxifloxacin. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Moxifloxacin

Wohlkonig, A., Chan, P., Fosberry, A., Homes, P., Huang, J., Kranz, M., Leydon, V., Miles, T., Pearson, N., Perera, R., Shillings, A., Gwynn, M., Bax, B. (2010). Structural basis of quinolone inhibition of type IIA topoisomerases and target-mediated resistance. Nature Structural & Molecular Biology, 17(9), pp.1152-1153. https://doi.org/10.1038/nsmb.1892 PDB ID: 2xkk

March 2025, Steven Arnold, Helen Gao, Shuchismita Dutta; Reviewed by Dr. James Berger
https://doi.org/10.2210/rcsb_pdb/GH/AMR/drugs/antibiotics/dna-synth/topo2/flqs/moxifloxacin