Bacteria Susceptible to Nitrofurantoin
Nitrofurantoin is highly effective against most common uropathogens, particularly Escherichia coli, Staphylococcus saprophyticus, and Enterococcus species, including vancomycin-resistant enterococci (VRE). 1, 2
Primary Susceptible Organisms
- Escherichia coli: Maintains excellent susceptibility despite increasing resistance to other antibiotics. E. coli remains highly susceptible to nitrofurantoin even when resistant to fluoroquinolones and trimethoprim-sulfamethoxazole 1, 3
- Staphylococcus saprophyticus: Highly susceptible with significant killing effect 3
- Enterococcus species: Including E. faecalis and E. faecium 4, 5
- Vancomycin-resistant enterococci (VRE): Notably, nitrofurantoin maintains activity against VRE, making it valuable for resistant infections 1, 4
Susceptibility Patterns
- Studies show 88% of Enterococcus isolates are susceptible to nitrofurantoin 5
- Among strains resistant to other antibiotics (ampicillin, co-trimoxazole, doxycycline, imipenem, and vancomycin), 50-88% remain susceptible to nitrofurantoin 5
- No resistance was found in 300 tested isolates of E. faecium, E. faecalis, and E. gallinarum, including vancomycin-resistant strains 4
Pharmacodynamic Properties
- Nitrofurantoin exhibits concentration-dependent bactericidal activity against E. coli 3
- The time above MIC (T>MIC) correlates best with antibacterial effect 3
- Requires bacterial nitroreductases for activation, which convert it to its active form 6
- Metabolic activity of bacteria can influence susceptibility - bacteria in stationary phase may be less susceptible unless metabolites are present 6
Clinical Applications
- Recommended as a first-line agent for uncomplicated lower urinary tract infections by WHO and IDSA guidelines 7, 1
- The WHO Essential Medicines list categorizes nitrofurantoin as an Access (A) category antibiotic for lower UTIs 7
- Particularly valuable in settings with high resistance to fluoroquinolones and trimethoprim-sulfamethoxazole 2
- Should not be used for pyelonephritis or systemic infections due to inadequate serum concentrations 1
Resistance Considerations
- Nitrofurantoin maintains high activity against E. coli despite increasing resistance to other antibiotics 2
- The susceptibility of E. coli to nitrofurantoin in urinary isolates remains generally high in both adults and children 7
- Nitrofurantoin becomes more cost-effective when fluoroquinolone-resistant E. coli exceeds 12% prevalence 7
Important Limitations
- Not effective for pyelonephritis or prostatitis due to poor tissue penetration 7, 1
- Contraindicated in patients with renal impairment and in the last trimester of pregnancy 1, 2
- Primarily excreted in urine, with poor tissue penetration, limiting its use to lower urinary tract infections 1
Nitrofurantoin's continued effectiveness against common uropathogens, including resistant strains, makes it a valuable option for uncomplicated urinary tract infections, particularly in an era of increasing antimicrobial resistance.