Quinolines and fluoroquinolones are antibacterial drugs that work by blocking bacterial DNA replication. They are widely used for urinary infections, respiratory infections, gastrointestinal infections, and other systemic bacterial diseases. Fluoroquinolones are improved versions of older quinolines and are more powerful, better absorbed, and have a broader antibacterial range.
Mechanism of Action
These drugs act by inhibiting bacterial enzymes needed for DNA functions:
- DNA gyrase (Topoisomerase II)
- Topoisomerase IV
Blocking these enzymes prevents the bacteria from replicating or repairing DNA, leading to bacterial death. This is why fluoroquinolones are considered bactericidal.
Classification
1. First-Generation Quinolines
- Nalidixic acid
- Oxolinic acid
These older drugs mainly act on gram-negative bacteria and are used mostly for urinary tract infections.
2. Second-Generation Fluoroquinolones
- Ciprofloxacin
- Ofloxacin
- Norfloxacin
- Lomefloxacin
They have strong gram-negative action and moderate gram-positive activity. Ciprofloxacin is one of the most commonly used fluoroquinolones.
3. Third-Generation Fluoroquinolones
- Levofloxacin
- Gatifloxacin
These have better action against gram-positive organisms and are widely used in respiratory infections.
4. Fourth-Generation Fluoroquinolones
- Moxifloxacin
- Gemifloxacin
These have broad-spectrum activity, including anaerobes.
Pharmacokinetics
- Well absorbed when taken orally
- Good distribution in tissues and body fluids
- Norfloxacin reaches lower serum levels (acts mainly in urinary tract)
- Eliminated mostly through kidneys
- Food delays but does not reduce absorption
Uses
1. Urinary Tract Infections (UTI)
Ciprofloxacin, norfloxacin, and ofloxacin are commonly used.
2. Respiratory Infections
- Levofloxacin and moxifloxacin
- Effective in pneumonia, bronchitis, sinusitis
3. Gastrointestinal Infections
- Ciprofloxacin is useful in infectious diarrhoea and typhoid fever
4. Bone and Joint Infections
- Ciprofloxacin penetrates well into bone
5. Skin and Soft Tissue Infections
Levofloxacin and moxifloxacin have good coverage.
6. Anthrax
Ciprofloxacin is the drug of choice for anthrax exposure.
Adverse Effects
- Nausea, vomiting, abdominal discomfort
- Headache, dizziness
- Photosensitivity
- Tendonitis and tendon rupture (risk higher in elderly)
- Prolonged QT interval (risk of arrhythmias)
- Joint and cartilage damage in children
Contraindications: Pregnancy, breastfeeding, and children under 18 years (except life-threatening conditions).
Drug Interactions
- Antacids containing magnesium or aluminium reduce absorption
- Increases levels of theophylline and warfarin
- Should not be combined with drugs that prolong QT interval
Bacterial Resistance
- Mutations in DNA gyrase or topoisomerase IV
- Reduced drug entry into bacteria
- Drug efflux pumps
Resistance develops faster with improper or overuse of these drugs.
Detailed Notes:
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