1. Generic & Brand Names
Generic: Nitrofurantoin
Brands:
Macrocrystalline: Macrobid® (100mg caps), Macrodantin® (25/50/100mg caps)
Monohydrate: Furadantin® (oral suspension)
Generics: Common in most markets
2. Drug Class & Mechanism
Class: Nitrofuran antibiotic
Mechanism:
Activated by bacterial reductases → damages DNA/RNA/proteins
Bacteriostatic at low doses, bactericidal at high concentrations
Spectrum:
Gram-negative: E. coli, Klebsiella, Enterobacter
Gram-positive: Enterococcus, S. saprophyticus
NOT for: Proteus, Pseudomonas, Serratia (produce drug-inactivating enzymes)
3. FDA-Approved Uses
| Indication | Details |
|---|---|
| Uncomplicated Cystitis | First-line for acute lower UTI |
| Prophylaxis | Recurrent UTI prevention (50-100mg at bedtime) |
4. Dosing Regimens
| Formulation | Acute UTI Treatment | Prophylaxis |
|---|---|---|
| Macrocrystalline (Macrobid®) | 100 mg q12h × 5-7 days | 100 mg at bedtime |
| Monohydrate (Furadantin®) | 50-100 mg q6h × 7 days | 50-100 mg at bedtime |
| Pediatric (≥1 month) | 5-7 mg/kg/day divided q6h | Not recommended |
Key Administration Rules:
Take with food/milk ↑ absorption + ↓ nausea
Avoid antacids ↓ efficacy
CrCl <60 mL/min: CONTRAINDICATED (↑ toxicity + subtherapeutic urine levels)
5. Side Effects
| Common (≥10%) | Serious (<1%) |
|---|---|
| Nausea/vomiting | Pulmonary Fibrosis (chronic use) |
| Headache | Hepatotoxicity (jaundice) |
| Brown urine (harmless) | Peripheral Neuropathy |
| Diarrhea | Hemolytic Anemia (G6PD deficiency) |
6. Black Box Warnings & Contraindications
🚫 Absolute Contraindications:
CrCl <60 mL/min
G6PD deficiency (risk of hemolysis)
Infants <1 month (risk of hemolytic anemia)
Pregnancy ≥38 weeks (risk of neonatal hemolysis)
Major Warnings:
Pulmonary reactions: Acute (fever, cough) or chronic (fibrosis) – discontinue immediately
Hepatic necrosis: Monitor LFTs with long-term prophylaxis
7. Drug Interactions
| Medication | Risk | Management |
|---|---|---|
| Antacids | ↓ Absorption | Separate by 2h |
| Probenecid | ↓ Urinary excretion → ↑ toxicity | Avoid combo |
| Uricosurics | ↓ Efficacy (e.g., sulfinpyrazone) | Monitor for failure |
8. Resistance Advantages
Resistance remains <5% in E. coli (vs. >25% for TMP-SMX)
No cross-resistance with fluoroquinolones/cephalosporins
Ideal for:
Community-acquired UTIs
Patients allergic to β-lactams
9. Special Populations
| Group | Recommendation |
|---|---|
| Pregnancy | Category B (avoid at term) |
| Breastfeeding | Avoid (infant hemolysis risk) |
| Elderly | Check CrCl before prescribing |
10. Storage & Handling
Capsules: 20-25°C; protect from moisture
Suspension: Refrigerate; discard after 7 days
Avoid heat/light (darkens drug → harmless but alarming)
Clinical Practice Guidelines
✅ First-Line for Uncomplicated Cystitis:
IDSA/ESCMID: 5-day nitrofurantoin = 3-day fosfomycin (cure rates 85-90%)
❌ Avoid For:Pyelonephritis (poor tissue penetration)
Prostatitis (no prostate penetration)
UTIs with suspected Proteus/Pseudomonas
⚠️ Renal Function Critical:
Nitrofurantoin vs. Alternatives for UTI
| Parameter | Nitrofurantoin | TMP-SMX | Fosfomycin |
|---|---|---|---|
| Resistance (E. coli) | 3-5% | 20-35% | 1-3% |
| Dosing | Twice daily | Twice daily | Single dose |
| Renal Safety | Avoid if CrCl<60 | OK down to CrCl>15 | Any function |
| Pregnancy | Limited use | Avoid (Category D) | Safe |
Patient Counseling
"Take with food to prevent upset stomach."
"Brown urine is normal – don't panic!"
"Stop immediately for:
Shortness of breath/cough (lung issues)
Yellow skin/eyes (liver problems)
Tingling hands/feet (nerve damage)"
"Do NOT use if pregnant near delivery."
💡 Pro Tip: For recurrent UTIs, vaginal estrogen (postmenopausal) or cranberry proanthocyanidins may reduce recurrence when combined with prophylaxis.
Prescribing Status: First-line for uncomplicated cystitis per IDSA guidelines. Monitor for pulmonary/hepatic toxicity with long-term use.
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