Description
Norfloxacin is the first of the third generation nalidixic acid analogs to reach the
marketplace. It exhibits potent in vitro and in vivo activity against Pseudomonas,
enteric gram-negative rods and gram-positive cocci. Norfloxacin is orally
effective in the treatment of urinary tract infections, including those due to
organisms refractory to many other agents.
Originator
Kyorin (Japan)
Definition
ChEBI: A quinolinemonocarboxylic acid with broad-spectrum antibacterial activity against most gram-negative and gram-positive bacteria. Norfloxacin is bactericidal and its mode of action depends on blocking of bacterial DNA replication by binding itself to an enz
me called DNA gyrase.
Manufacturing Process
36 g (0.134 mol) of 7-chloro-1-ethyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3carboxylic acid, 46 g of piperazine and 210 cm3 of pyridine were heated under reflux for 6 hours, while stirring. After the starting material had dissolved, a precipitate appeared after heating for about 2 hours 30 minutes. The major part of the solvent was removed by concentration in vacuo (15 mm Hg; 100°C). In order to remove the pyridine as completely as possible, the residue was taken up in 200 cm3of water and the concentration in vacuo was repeated.
The residue, resuspended in 150 cm3 of water, was stirred. 150 cm3 of 2N NaOH were added thereto. The solution, which was slightly turbid, was treated with 5 g of animal charcoal and stirred for 30 minutes. After filtration, the pH was brought to 7.2 by adding acetic acid while stirring. The precipitate was filtered off, washed with water and dissolved in 250 cm3 of a 10% aqueous acetic acid. The acid solution (pH 4.4) was filtered and then brought to pH 7.2 by gradually added 2N NaOH.
The suspension was heated to 90°C, while stirring. The crystals were separated and recrystallized from 280 cm3 of a mixture of DMF (1 volume) and ethanol (4 volumes). After drying in vacuo over phosphorus pentoxide, 29.5 g (yield 70%) of 1-ethyl-6-fluoro-4-oxo-7-piperazinyl-1,4dihydroquinoline-3-carboxylic acid, melting point 222°C, were obtained.
In air, this product is hygroscopic and gives a hemihydrate.
Brand name
Chibroxin (Merck); Noroxin (Merck).
Therapeutic Function
Antibacterial
Antimicrobial activity
It is active against a wide range of Gram-negative bacteria, including Enterobacteriaceae and Campylobacter spp. Ps. aeruginosa, Acinetobacter, Serratia and Providencia spp. are weakly susceptible (and often resistant). It has no useful activity against anaerobes, Chlamydia, Mycoplasma and Mycobacterium spp.
Pharmaceutical Applications
A 6-fluoro, 7-piperazinyl quinoline available for oral administration and as an ophthalmic ointment.
Pharmacokinetics
Oral absorption: 50–70%
Cmax 400 mg oral :1.5 mg/L after 1–1.5 h
Plasma half-life :3–4 h
Volume of distribution: 2.5–3.1 L/kg
Plasma protein binding: 15%
absorption and distribution
Norfloxacin displays linear kinetics. There is no significant accumulation with the recommended dosage of 400 mg every 12 h. Food slightly delays but does not otherwise impair absorption. Antacids reduce absorption. It is widely distributed, but concentrations in tissues other than those of the urinary tract are low： levels in the prostate are around 2.5 mg/g.
Metabolism and excretion
Six or more inactive metabolites are produced. Around 30% of a dose appears as unchanged drug in the urine and <10% as metabolites, producing peak concentrations of microbiologically active drug of around 100–400 mg/L. Urinary recovery is halved by probenecid, with little effect on the plasma concentration. The apparent plasma elimination half-life increases with renal impairment, rising to around 8 h in the anuric patient. Some of the drug appears in the bile where concentrations three- to seven-fold greater than the simultaneous plasma levels are achieved, but this is not a significant route of elimination and hepatic impairment is without effect. Very variable quantities, averaging 30% of a dose, appear in the feces, producing concentrations of active agent of around 200–2000 mg/kg.
Clinical Use
Complicated and uncomplicated urinary tract infections (including prophylaxis in recurrent infections), prostatitis
Uncomplicated gonorrhea
Gastroenteritis caused by Salmonella, Shigella and Campylobacter spp., Vibrio cholerae
Conjunctivitis (ophthalmic preparation)
Side effects
Untoward reactions are those common to the fluoroquinolones. Gastrointestinal tract disturbances, which are generally mild, have been reported in 2–4% of patients. CNS disturbances have largely been limited to headache, drowsiness and dizziness. Co-administration with theophylline results in increased plasma theophylline levels.
Safety Profile
Poison by intravenous route.Moderately toxic by other routes. Human systemic effectsby ingestion: musculoskeletal changes. An experimentalteratogen. Other experimental reproductive effects.Mutation data reported. When heated to decomposition itemits
Synthesis
Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-
quinolincarboxylic acid (33.2.18), is the first representative of a series of fluorinated
quinolones as well as the first drug of the quinolone derivatives used in medicine that contains a piperazine substituent. The method of synthesis is basically the same as that suggested for synthesizing nalidixic and oxolinic acids.
Reacting 3-chloro-4-fluoroaniline and ethyl ethoxymethylenmalonate gives the substitution product (33.2.15), which upon heating in diphenyl ester cyclizes into ethyl ester of
6-fluoro-7-chloro-1,4-dihydro-3-quinolin-4-on-carboxylic acid (33.2.16). Direct treatment
of the product with ethyl iodide in the presence of triethylamine and subsequent hydrolysis with a base gives 1-ethyl-6-fluoro-7-chloro-1,4-dihydro-3-quinolin-4-on-carboxylic
acid (33.2.17). Reacting this with piperazine gives norfloxacin (33.2.18).
Drug interactions
Potentially hazardous interactions with other drugs
Aminophylline: possibly increased risk of
convulsions, increased levels of aminophylline.
Analgesics: increased risk of convulsions with
NSAIDs.
Anticoagulants: anticoagulant effect of coumarins
enhanced.
Antimalarials: manufacturer of artemether with
lumefantrine advises avoid.
Ciclosporin: increased risk of nephrotoxicity.
Muscle relaxants: possibly increases tizanidine
concentration.
Theophylline: possibly increased risk of convulsions;
increased levels of theophylline.
Metabolism
Some metabolism occurs, possibly in the liver.
Norfloxacin is eliminated through metabolism, biliary
excretion and renal excretion. Renal excretion occurs by
both glomerular filtration and net tubular secretion. In
the first 24 hours, 33-48% of the drug is recovered in the
urine.
Norfloxacin exists in the urine as norfloxacin and six
active metabolites of lesser antimicrobial potency.
The parent compound accounts for over 70% of total
excretion. About 30% of an oral dose appears in the
faeces.
