Nitrofurantoin
Brand names: Macrobid, Macrodantin
Class: 💉 Penicillins, Cephalosporins & UTI Antibiotics
The AANP exam tests nitrofurantoin as a first-line agent for uncomplicated cystitis — and demands you remember the two situations where you must avoid it. It concentrates in the urine and treats lower UTI only; it does not reach therapeutic levels in the kidney parenchyma or bloodstream, so it is wrong for pyelonephritis or bacteremia. Avoid in CrCl <30 (insufficient urine concentration and accumulation toxicity) and at 36+ weeks of pregnancy or during labor (neonatal hemolysis in G6PD-deficient infants). Take with food to improve absorption and reduce nausea. Long-term suppressive use carries pulmonary fibrosis and hepatotoxicity risk. The trigger phrase on the exam — uncomplicated cystitis with normal renal function — is the nitrofurantoin question.
✅ Indications
Uncomplicated cystitis (lower UTI only) — NOT for pyelonephritis.
⚙️ Mechanism of Action
Multiple intracellular targets; concentrated in urine only.
📏 Dosing
100 mg PO BID × 5 days.
🚫 Contraindications
CrCl <30 mL/min (inadequate urinary concentration), pregnancy near term (38–42 wk, hemolytic anemia), G6PD deficiency.
⚠️ Adverse Effects
GI upset, pulmonary hypersensitivity (acute pneumonitis + chronic fibrosis with long-term use), hepatotoxicity, peripheral neuropathy, hemolysis (G6PD).
🔬 Monitoring
CrCl before start; watch for pulmonary symptoms with long-term prophylaxis.
💎 Board Pearls
- 🚫 ONLY lower UTI — does NOT penetrate kidney tissue (no pyelo coverage).
- 🩸 Avoid CrCl <30 — won't concentrate in urine.
- 🤰 Safe most of pregnancy EXCEPT 38–42 weeks (hemolytic anemia in newborn).
- 🫁 Long-term prophylaxis → pulmonary fibrosis risk.
Practice Questions
A 32-year-old G2P1 woman at 39 weeks gestation calls the clinic with 2 days of dysuria, urinary frequency, and suprapubic discomfort. She is afebrile and denies flank pain or contractions. A UA obtained yesterday is positive for leukocyte esterase and nitrites. Her records note no drug allergies. Which of the following antibiotic plans is LEAST appropriate to phone in for her today?
Related Drugs in This Class
- Amoxicillin — Amoxil
- Amoxicillin-Clavulanate — Augmentin
- Cephalexin — Keflex
- Trimethoprim-Sulfamethoxazole — Bactrim, Septra, TMP-SMX
Sources
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