Ciprofloxacin chemical structure (fluoroquinolone), 2D skeletal formula, C17H18FN3O3

Ciprofloxacin Chemical Structure

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1. Identification

Summary

Ciprofloxacin is a second-generation fluoroquinolone antibiotic used for a wide range of susceptible infections (e.g., urinary tract, GI, bone/joint, some lower respiratory infections) and available as oral, IV, ophthalmic, and otic products. Class labeling carries serious safety warnings (e.g., tendon rupture, neuropathy, CNS effects), so use is guided by risk–benefit and local stewardship.

Brand Names

Cipro, Cipro XR, Ciloxan (ophthalmic), Cetraxal (otic), and many generics (region-dependent)

Name

Ciprofloxacin

Background

A synthetic quinolone introduced in the 1980s; the hydrochloride salt is common for oral tablets/suspensions, while topical products use hydrochloride solutions. It inhibits bacterial DNA processes via topoisomerase targets (see Pharmacology).

Modality

Small molecule

Groups

Approved; prescription

Structure

Ciprofloxacin chemical structure (fluoroquinolone), 2D skeletal formula, C17H18FN3O3
Ciprofloxacin 2D chemical structure (quinolone carboxylic acid). Formula C17H18FN3O3; IUPAC long name; CAS 85721-33-1.

Weight

≈ 331.35 g/mol (free base)

Chemical Formula

C₁₇H₁₈FN₃O₃ (free base)

Synonyms

1-Cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)quinoline-3-carboxylic acid; ciprofloxacin free base; ciprofloxacin HCl (salt form)

External IDs

CAS (base): 85721-33-1; PubChem CID: 2764; UNII (base): 5E8K9I0O4U; KEGG: D00186; ChEMBL: 8; ChEBI: 100241; ATC (systemic): J01MA02

2. Pharmacology

Indication

Treatment of susceptible infections (e.g., UTI/pyelonephritis, infectious diarrhea/typhoid, certain bone/joint infections, prostatitis, post-exposure inhalational anthrax, plague); ophthalmic/otic forms for bacterial conjunctivitis/corneal ulcer and otitis indications per label.

Associated Conditions

Complicated/acute uncomplicated UTI, traveler’s diarrhea, intra-abdominal infections (with adjuncts), osteomyelitis, selected lower respiratory infections (pathogen-specific), ocular/otic infections (topical).

Associated Therapies

Often combined with metronidazole (intra-abdominal), or dexamethasone/hydrocortisone in otic combos; avoid routine co-use with other QT-prolonging or strong CYP1A2 substrates without assessment.

Contraindications & Blackbox Warnings

Fluoroquinolone boxed warnings: tendinitis/tendon rupture, peripheral neuropathy, CNS effects; may exacerbate myasthenia gravis. Additional FDA warnings highlight aortic aneurysm/dissection risk in susceptible patients; restrict use for uncomplicated infections when risks outweigh benefits. Tizanidine is contraindicated with ciprofloxacin (CYP1A2 inhibition). DailyMed+2U.S. Food and Drug Administration+2

Pharmacodynamics

Bactericidal, concentration-dependent killing via inhibition of bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, blocking DNA replication, transcription, and repair.

Mechanism of action

Fluorinated quinolone core binds gyrase/topo IV–DNA complexes, stabilizing double-strand breaks and leading to rapid bacterial cell death.

Absorption

Oral bioavailability ~70%; food may delay tₘₐₓ but not overall exposure. Avoid co-administration with polyvalent cations (e.g., Al/Mg antacids, iron, zinc, sucralfate): they markedly reduce absorption; separate doses (e.g., ≥2 h before or ≥6 h after). DailyMed

Volume of distribution

Large; typically ~2–3 L/kg, reflecting extensive tissue penetration (e.g., urine, prostate, lungs, skin, bone). NCBI+1

Protein binding

~20–40%. DailyMed

Metabolism

Hepatic biotransformation to several metabolites; ciprofloxacin is a CYP1A2 inhibitor (interaction relevance—see Interactions). DailyMed

Route of elimination

Primarily renal as unchanged drug (≈40–50% oral dose) with additional fecal/biliary excretion and minor active metabolites. DailyMed

Half-life

About ~4 hours in normal renal function (slightly prolonged with impairment). DailyMed

Clearance

Renal clearance ~300 mL/min (active tubular secretion contributes); reduced by probenecid. DailyMed

Adverse Effects

GI upset, headache, dizziness, photosensitivity; serious class effects include tendinopathy/rupture, peripheral neuropathy, CNS effects (seizures, psychosis), QT prolongation, dysglycemia, aortic aneurysm risk, and C. difficile–associated diarrhea. DailyMed

Toxicity

Overdose: supportive management; crystalluria risk mitigated by hydration. Hemodialysis removes little drug. DailyMed

Pathways

Topoisomerase targeting (DNA gyrase/topo IV); distribution via passive/active transport; renal tubular secretion.

Pharmacogenomic Effects/ADRs

No routine PGx testing; CYP1A2 interactions are clinically significant; tendon risk increased with age and concurrent corticosteroids. DailyMed

3. Interactions

Drug Interactions

  • Contraindicated: Tizanidine (↑ exposure via CYP1A2 inhibition, severe hypotension/sedation). DailyMed
  • Chelation/complexation: Al/Mg antacids, sucralfate, iron, zinc, calcium—marked ↓ absorption; separate dosing. DailyMed
  • CYP1A2 substrates: Theophylline, caffeine, ropinirole, clozapine, tizanidine, sildenafil—↑ levels; monitor/avoid as labeled. DailyMed
  • Probenecid: ↓ renal clearance → ↑ ciprofloxacin exposure. DailyMed

Food Interactions

May take with food; avoid dairy/calcium-fortified juices alone (reduce exposure). Take with a mixed meal if needed. DailyMed

4. Categories

ATC Codes

J01MA02 (systemic fluoroquinolone), S01AE03 (ophthalmic), S02AA15 (otic antiinfective); combination otic codes exist (e.g., S02CA05/06 with corticosteroids). atcddd.fhi.no+2atcddd.fhi.no+2

Drug Categories

Fluoroquinolone; Antibacterial; Small molecule; Topoisomerase inhibitor (bacterial)

Chemical Taxonomy

Quinolone carboxylic acid with piperazinyl and cyclopropyl substituents; fluorinated at C-6.

Affected organisms

Humans (therapeutic use); target bacteria susceptible to fluoroquinolones

5. Chemical Identifiers

UNII

5E8K9I0O4U (ciprofloxacin, base) precisionFDA

CAS number

85721-33-1 (base) precisionFDA

InChI Key

MYSWGUAQZAJSOK-UHFFFAOYSA-N PubChem

InChI

InChI=1S/C17H18FN3O3/c18-13-7-11-14(8-15(13)20-5-3-19-4-6-20)21(10-1-2-10)9-12(16(11)22)17(23)24/h7-10,19H,1-6H2,(H,23,24) Wikipedia

IUPAC Name

1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)-quinoline-3-carboxylic acid Wikipedia

SMILES

C1CNCCN1c(c2)c(F)cc3c2N(C4CC4)C=C(C3=O)C(=O)O Wikipedia

6. References

  1. DailyMed: Ciprofloxacin tablets—PK (bioavailability ~70%, protein binding 20–40%, t½ ~4 h), interactions (antacids/cations), tizanidine contraindication, renal clearance details. DailyMed
  2. PubChem (CID 2764): Molecular formula C₁₇H₁₈FN₃O₃, MW ≈331.35 g/mol; identifiers. PubChem
  3. FDA GSRS / precision.fda (UNII): Ciprofloxacin UNII 5E8K9I0O4U, CAS 85721-33-1. precisionFDA+1
  4. ATC/DDD Index (FHI): J01MA02; topical codes S01AE03, S02AA15 listings. atcddd.fhi.no+2atcddd.fhi.no+2
  5. StatPearls (NCBI Bookshelf): Distribution ~2–3 L/kg and clinical use overview. NCBI
  6. FDA Drug Safety Communications: Fluoroquinolone warnings including aortic aneurysm/dissection risk; reinforce boxed warnings. U.S. Food and Drug Administration+1

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