Norfloxacin

MECHANISM OF ACTION

Norfloxacin is a fluoroquinolone antibiotic that works by inhibiting bacterial DNA synthesis. It blocks the activity of DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for DNA replication, transcription, and repair. This disruption leads to the prevention of bacterial cell division and ultimately causes bacterial cell death, making it a bactericidal agent.

PHARMACOKINETICS

Absorption: Rapidly absorbed after oral administration. Peak serum concentrations occur within 1–2 hours post-dose. Bioavailability is approximately 57%. Food may delay absorption.

Distribution: Low protein binding (≤30%). It has a high volume of distribution((1.5-3.1L/Kg, indicating excellent tissue penetration, particularly in the kidney, prostate, bile, and urine.

Metabolism: Partially metabolized in the liver. Both the parent drug and its metabolites are active.

Elimination: The primary route of excretion is renal via glomerular filtration and tubular secretion. Around 30% of an oral dose is excreted unchanged in the urine.

PHARMACODYNAMICS

Norfloxacin is a fluoroquinolone antibiotic that exerts its pharmacodynamic effect by inhibiting bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for DNA replication, transcription, and repair. This inhibition leads to disruption of bacterial DNA synthesis, preventing cell division and resulting in bacterial cell death. It is bactericidal and shows concentration-dependent killing, with greater effectiveness at higher drug concentrations.

ADMINISTRATION

Norfloxacin is administered orally in tablet or suspension form, usually taken on an empty stomach with water to enhance absorption. It is typically given twice daily, with dosing adjusted based on the type and severity of infection, commonly for urinary tract and gastrointestinal infections. Patients are advised to avoid taking it with dairy products or antacids containing calcium, magnesium, or aluminum, as these can reduce drug absorption. The full prescribed course should be completed to prevent resistance and recurrence of infection.

DOSAGE AND STRENGTH

Available strength:

• 400 mg tablets (most common)

• Usual adult dose:

• 400 mg twice daily

Treatment duration:

• Uncomplicated UTI: 3–7 days

• Complicated infections: longer duration as prescribed

Dose adjustment:

• May be required in renal impairment patients

FOOD INTERACTIONS

Norfloxacin should ideally be taken on an empty stomach, as food can reduce and delay its absorption. Dairy products and mineral-rich supplements containing calcium, magnesium, aluminum, or iron can significantly decrease its effectiveness by forming insoluble complexes. Therefore, it is recommended to avoid taking it together with milk, antacids, or multivitamins containing these minerals.

DRUG INTERACTIONS

Norfloxacin interacts with several drugs that can reduce its absorption or alter its effects. Antacids, sucralfate, and supplements containing calcium, magnesium, aluminum, or iron can significantly decrease its bioavailability. Probenecid may reduce renal excretion and increase drug levels. Theophylline levels may be elevated, increasing toxicity risk. It may also enhance the effects of oral anticoagulants like warfarin, increasing bleeding risk. Concomitant use with NSAIDs may increase the risk of central nervous system stimulation and seizures.

CONTRAINDICATIONS

Norfloxacin is contraindicated in patients who are hypersensitive to norfloxacin or other fluoroquinolones such as ciprofloxacin and levofloxacin. It should not be given to individuals with a previous history of tendonitis or tendon rupture associated with quinolone therapy. Its use is also generally avoided in children, adolescents, and patients suffering from myasthenia gravis.

SIDE EFFECTS

• Nausea

• Vomiting

• Abdominal pain

• Diarrhea

• Headache

• Dizziness

• Insomnia

• Skin rash or itching

• Photosensitivity (increased sensitivity to sunlight)

• Tendon pain or inflammation (rare but serious)

• Central nervous system effects (confusion, agitation, in rare cases seizures)

OVERDOSE

A norfloxacin overdose requires urgent medical care. It may present with severe gastrointestinal symptoms such as nausea and diarrhea, along with dizziness, confusion, and possible central nervous system effects like seizures. There is no specific antidote available, so management is mainly supportive, including measures such as gastric lavage, induced vomiting when appropriate, and adequate hydration to prevent crystalluria.

TOXICITY

Norfloxacin, a fluoroquinolone antibiotic, is associated with potentially serious and sometimes irreversible toxic effects, including tendon rupture, peripheral neuropathy, and central nervous system reactions such as seizures and psychosis. More common adverse effects include nausea, headache, dizziness, and gastrointestinal disturbances. It has also been linked to severe reactions such as QT interval prolongation and liver dysfunction, with recent reports noting cases of skin hyperpigmentation.