1. Clinical Overview
Nitrofurantoin is a synthetic nitrofuran derivative antibiotic specifically indicated for the treatment and prophylaxis of uncomplicated lower urinary tract infections (UTIs) caused by susceptible strains of Escherichia coli, Staphylococcus saprophyticus, Enterococcus faecalis, and certain strains of Klebsiella and Enterobacter species. Its unique property is achieving high concentrations in the urine while maintaining low serum levels, making it unsuitable for systemic infections. The 25mg/5ml oral suspension is a common pediatric formulation in India.
| Onset | Duration | Bioavailability |
|---|---|---|
| Urinary antibacterial concentrations are achieved within 30 minutes to 1 hour after oral administration. | Approximately 6 to 8 hours, necessitating multiple daily dosing. | Approximately 90% for the macrocrystalline form (common in suspensions), with rapid and complete absorption from the gastrointestinal tract. |
2. Mechanism of Action
Nitrofurantoin is a prodrug. It is taken up by susceptible bacteria via passive diffusion and, to a greater extent, by energy-dependent bacterial transport systems. Inside the bacterial cell, it is reduced by bacterial nitroreductases (flavoproteins) to highly reactive electrophilic intermediates. These intermediates attack and damage bacterial ribosomal proteins, DNA, RNA, and other critical macromolecules, leading to inhibition of the acetyl coenzyme A pathway, aerobic energy metabolism, and cell wall synthesis.
3. Indications & Uses
- Treatment of acute, uncomplicated cystitis caused by susceptible strains of E. coli, S. saprophyticus, and Enterococcus faecalis.
- Prophylaxis of recurrent urinary tract infections (long-term, low-dose therapy).
4. Dosage & Administration
Adult Dosage: For treatment: 50 to 100 mg (10 to 20 ml of 25mg/5ml suspension) four times daily for 5 to 7 days. For prophylaxis: 50 to 100 mg (10 to 20 ml) once daily at bedtime.
Administration: Administer with food or milk to improve tolerance, enhance absorption, and reduce gastrointestinal side effects. Shake the oral suspension well before each use. Use the measuring cup/spoon provided. Complete the full prescribed course even if symptoms improve earlier.
5. Side Effects
Common side effects may include:
- Nausea
- Anorexia (loss of appetite)
- Abdominal pain
- Diarrhea
- Headache
- Brownish discoloration of urine (harmless)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Antacids containing Magnesium Trisilicate | Reduces absorption and bioavailability of nitrofurantoin. | Moderate |
| Probenecid | Inhibits renal tubular secretion of nitrofurantoin, leading to increased serum levels and decreased urinary concentrations, potentially reducing efficacy and increasing toxicity. | Major |
| Sulfinpyrazone | Similar to probenecid, inhibits excretion, increases toxicity. | Major |
| Uricosuric Agents (e.g., Benzbromarone) | May decrease renal excretion of nitrofurantoin. | Moderate |
| Drugs causing Peripheral Neuropathy (e.g., Statins, Colchicine, Metronidazole, Isoniazid) | Additive risk of neuropathy. | Moderate |
| Live Bacterial Vaccines (e.g., Typhoid oral vaccine) | Antibiotics may diminish therapeutic effect of live vaccines. | Moderate |
7. Patient Counselling
- DO take with food or milk to reduce stomach upset.
- DO shake the suspension well before measuring each dose.
- DO use the measuring device provided with the medicine, not a household spoon.
- DO complete the full course of medicine even if you feel better.
- DO drink plenty of fluids (water) while on this medication.
- DONT take antacids containing magnesium trisilicate at the same time. Separate by at least 2 hours.
- DONT use if you are pregnant at term (38-42 weeks).
- DONT use if you have known severe kidney problems.
8. Toxicology & Storage
Overdose: Symptoms are primarily related to exaggerated pharmacological effects: severe nausea, vomiting, and gastrointestinal distress. In cases of massive overdose or in patients with renal impairment, systemic toxicity such as neurotoxicity (seizures, polyneuropathy) could occur.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Do not freeze. Keep the bottle tightly closed. Keep out of reach of children. Discard any unused suspension after the course of treatment is completed or by the expiry date, whichever is earlier.