Urinary tract anti-infective agents are drugs used to treat infections of the urinary system, including infections of the kidney (pyelonephritis), bladder (cystitis), and urethra (urethritis). These drugs act either by directly killing bacteria or by preventing their growth in the urinary tract.
Many UTI-causing organisms include E. coli, Klebsiella, Proteus, Pseudomonas, and other Gram-negative bacteria. Drug selection depends on the site of infection, severity, and susceptibility of the organism.
Classification of Urinary Anti-Infective Agents
- Urinary Antiseptics
- Nitrofurantoin
- Methenamine
- Phenazopyridine
- Sulfonamides
- Sulfisoxazole
- Co-trimoxazole (Trimethoprim + Sulfamethoxazole)
- Quinolones / Fluoroquinolones
- Norfloxacin
- Ciprofloxacin
- Ofloxacin
- Miscellaneous
- Nalidixic acid
- Pipemidic acid
- Fosfomycin
Urinary Antiseptics
Nitrofurantoin
Mechanism: Reduced inside bacterial cells into reactive intermediates that damage DNA, ribosomes, and metabolic enzymes.
Spectrum: Mainly Gram-negative bacteria.
Uses: Uncomplicated lower UTIs.
Side effects: Nausea, vomiting, pulmonary toxicity (rare but serious).
Methenamine
Mechanism: Releases formaldehyde in acidic urine, which acts as an antibacterial agent.
Uses: Chronic or recurrent UTI prophylaxis.
Notes: Ineffective if urine is not acidic.
Phenazopyridine
Not an antibiotic — used as a urinary tract analgesic.
Effect: Provides symptomatic relief (pain, burning).
Side effects: Turns urine orange-red.
Sulfonamides
Sulfisoxazole
Mechanism: Inhibits folic acid synthesis (bacteriostatic).
Uses: Lower UTIs caused by susceptible organisms.
Co-trimoxazole (TMP + SMX)
Mechanism: Sequential blockade of folic acid pathway; bactericidal combination.
Uses: Uncomplicated UTIs, especially when E. coli is involved.
Advantages: Broad activity, low cost.
Quinolones and Fluoroquinolones
Norfloxacin
First-generation fluoroquinolone commonly used for UTIs.
Mechanism: Inhibits DNA gyrase and topoisomerase IV.
Use: Effective against most UTI pathogens.
Ciprofloxacin
Spectrum: Broad-spectrum, including Pseudomonas.
Uses: Complicated and non-complicated UTIs.
Ofloxacin
Highly effective, good oral absorption.
Miscellaneous Agents
Nalidixic Acid
Older quinolone effective only for Gram-negative bacteria.
Mechanism: Interferes with DNA replication.
Pipemidic Acid
Used in uncomplicated UTIs; similar to nalidixic acid.
Fosfomycin
Mechanism: Inhibits bacterial cell wall synthesis.
Use: Single-dose therapy for uncomplicated UTI (especially in women).
General Mechanisms of Action
- Inhibition of DNA synthesis: Fluoroquinolones, nalidixic acid
- Inhibition of folic acid pathway: Sulfonamides, trimethoprim
- Bacterial enzyme inhibition: Nitrofurantoin
- Release of formaldehyde in urine: Methenamine
Therapeutic Considerations
- Drug choice depends on pathogen sensitivity.
- Fluoroquinolones are avoided in pregnancy and children.
- Nitrofurantoin is preferred in pregnancy (except near term).
- Resistance patterns should be reviewed before antibiotic selection.
- Hydration helps flush the urinary tract and improve drug action.
Detailed Notes:
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