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Nitrofurantoin: Side Effects, Contraindications, and Dosage

Mechanism of Action of Nitrofurantoin

Nitrofurantoin is a bacteriostatic antibiotic. The substance is reduced by bacterial enzymes (nitroreductases) to reactive metabolites, which damage bacterial DNA and other enzymes.

Antibiotic spectrum of Nitrofurantoin:

Nitrofurantoin is effective against most Gram-positive and Gram-negative bacteria that cause urinary tract infections (E. coli, Klebsiella, enterococci, Enterobacter, and staphylococci). In Germany, 86% of pathogens causing uncomplicated cystitis are sensitive to nitrofurantoin (S3 guideline for UTI). It is generally not effective against Proteus mirabilis and Pseudomonas aeruginosa.

Urological Indications for Nitrofurantoin:

• Treatment of uncomplicated urinary tract infection in women.
• Treatment and prophylaxis of recurrent (complicated) urinary tract infections.

Pharmacokinetics of Nitrofurantoin:

• Almost complete absorption of nitrofurantoin after oral administration. The sustained-release form with macrocrystals delays absorption, prevents toxic plasma concentrations, and allows for longer dosing intervals.
• Partial enzymatic metabolism to inactive metabolites. Rapid renal elimination of the active ingredient and inactive metabolites (50%) through filtration and tubular secretion; brown discoloration of the urine is possible. The half-life of nitrofurantoin is 20–30 min.
• Good kidney function is necessary for effective concentration in the urine. In patients with renal insufficiency, there is a risk of toxic serum concentrations and insufficient urine concentrations.

Side effects of Nitrofurantoin:

Significant side effects are possible in some cases, especially during long-term therapy. Treatment must be discontinued immediately if the following symptoms occur: shortness of breath, cough, fever, cholestasis, or neurological symptoms. Blood counts and liver and kidney function tests are necessary during long-term therapy with nitrofurantoin.

Lung:

Interstitial pneumonia and even fatal pulmonary fibrosis have been observed with the use of nitrofurantoin. Discontinue treatment immediately if respiratory symptoms occur.

Allergy:

Drug fever and exanthema are possible, very rare, severe skin reactions.

Liver:

Common: Increased transaminases. In isolated cases, toxic liver failure.

Gastrointestinal tract:

Common: nausea, vomiting, and less common diarrhea.

CNS:

Common: vertigo, ataxia, and headaches. Very rare: psychotic reactions, depression, or polyneuropathy.

Blood:

Very rare: severe bone marrow depression.

Contraindications of Nitrofurantoin:

• Hypersensitivity to nitrofurantoin
• Renal insufficiency with a GFR below 45 ml/min
• Abnormal liver enzymes
• Glucose-6-phosphate dehydrogenase deficiency
• Polyneuropathy
• Pregnancy in the last trimester, premature infants, and infants up to the end of the third month of life.

Drug Interactions with Nitrofurantoin:

Urine acidification with methionine increases the effectiveness of nitrofurantoin. Do not administer nitrofurantoin and quinolones simultaneously.

Dosage of Nitrofurantoin:

• Uncomplicated cystitis: 100 mg sustained release 1-0-1 or 1-1-1 over 5–7 days. The maximum daily dose for children and adults should not exceed 5 mg/kg body weight.
• Therapy of complicated urinary tract infections (urinary bladder emptying disorders, DK carriers): 100 mg 1-0-1 or 0-0-1 for a maximum of 14 days. The daily dose for children and adults should not exceed 2–3 mg/kg body weight.
• Prophylaxis of recurrent urinary tract infections: 50–100 mg sustained release 0-0-1 for a maximum of six months. The daily dose for children and adults should not exceed 1.2 mg/kg body weight.

References

H. R. Brodt, A. Hörauf, M. Kresken, W. Solbach, and T. Welte, Infektionstherapie: Antibiotika, Virostatika, Antimykotika, Antiparasitäre Wirkstoffe. Thieme, 2023.

DGU, DEGAM, and PEG, “S3 Leitlinie Epidemiologie, Diagnostik, Therapie, Prävention und Management unkomplizierter, bakterieller, ambulant erworbener Harnwegsinfektionen bei erwachsenen Patienten Aktualisierung 2024.” [Online]. Available: https://register.awmf.org/assets/guidelines/043-044l_S3_Epidemiologie-Diagnostik-Therapie-Praevention-Management-Harnwegsinfektione-Erwachsene-HWI_2024-09.pdf

  Deutsche Version: Nitrofurantoin

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