Macrobid, Macrodantin
Classifications: urinary tract antibiotic;
Therapeutic: urinary tract antibiotic

Pregnancy Category: B


25 mg/mL suspension; 25 mg, 50 mg, 100 mg capsules


Synthetic nitrofuran derivative presumed to act by interfering with several bacterial enzyme systems. Highly soluble in urine and reportedly most active in acid urine. Antimicrobial concentrations in urine exceed those in blood.

Therapeutic Effect

Active against wide variety of gram-negative and gram-positive microorganisms.


Pyelonephritis, pyelitis, and cystitis caused by susceptible organisms.


Anuria, oliguria, significant impairment of kidney function (Clcr <60 mL/min); G6PD deficiency; infants <1 mo; pregnancy at term (38–42 wk), labor, or obstetric delivery.

Cautious Use

History of asthma, anemia, diabetes, vitamin B deficiency, hepatic disease; pulmonary disease; mild to moderate renal disease; electrolyte imbalance, debilitating disease; B12 deficiency; pregnancy (category B).

Route & Dosage

Pyelonephritis, Cystitis
Adult: PO 50–100 mg q.i.d. x 7 d or Macrobid 100 mg b.i.d. x 7 d
Child (1 mo–12 y): PO 5–7 mg/kg/d in 4 divided doses (max: 400 mg/d)

Chronic Suppressive Therapy
Adult: PO 50–100 mg h.s.
Child (1 mo–12 y): PO 1–2 mg/kg/d in 1–2 divided doses (max: 100 mg/d)

Renal Impairment
Avoid if Clcr <60 mL/min.


  • Give with food or milk to minimize gastric irritation.
  • Avoid crushing tablets because of the possibility of tooth staining; rather dilute oral suspension in milk, water, or fruit juice, and rinse mouth thoroughly after taking drug.

Adverse Effects (≥1%)

CNS: Peripheral neuropathy, headache, nystagmus, drowsiness, vertigo. GI: Anorexia, nausea, vomiting, abdominal pain, diarrhea, cholestatic jaundice, hepatic necrosis. Hematologic (rare): Hemolytic or megaloblastic anemia (especially in patients with G6PD deficiency), granulocytosis, eosinophilia. Body as a Whole: Angioedema, anaphylaxis, drug fever, arthralgia. Respiratory: Allergic pneumonitis, asthmatic attack (patients with history of asthma), pulmonary sensitivity reactions (interstitial pneumonitis or fibrosis). Skin: Skin eruptions, pruritus, urticaria, exfoliative dermatitis, transient alopecia. Urogenital: Genitourinary superinfections (especially with Pseudomonas), crystalluria (older adult patients), dark yellow or brown urine. Other: Tooth staining from direct contact with oral suspension and crushed tablets (infants).

Diagnostic Test Interference

Nitrofurantoin metabolite may produce false-positive urine glucose test results with Benedict's reagent.


Drug: antacids may decrease absorption of nitrofurantoin; nalidixic acid, other quinolones may antagonize antimicrobial effects; probenecid, sulfinpyrazone increase risk of nitrofurantoin toxicity.


Absorption: Readily from GI tract. Peak: Urine: 30 min. Distribution: Crosses placenta; distributed into breast milk. Metabolism: Partially in liver. Elimination: Primarily in urine. Half-Life: 20 min.

Nursing Implications

Assessment & Drug Effects

  • Lab tests: Perform C&S prior to therapy; recommended in patients with recurrent infections.
  • Monitor I&O. Report oliguria and any change in I&O ratio. Drug should be discontinued if oliguria or anuria develops or creatinine clearance falls below 40 mL/min.
  • Be alert to signs of urinary tract superinfections (e.g., milky urine, foul-smelling urine, perineal irritation, dysuria).
  • Assess for nausea (which occurs fairly frequently). May be relieved by using macrocrystalline preparation (Macrodantin) or by reducing dosage.
  • Watch for acute pulmonary sensitivity reaction, usually within first week of therapy and apparently more common in older adults. May be manifested by mild to severe flu-like syndrome. Eosinophilia generally develops in a few days. Recovery usually occurs rapidly after drug is discontinued.
  • With prolonged therapy, monitor for subacute or chronic pulmonary sensitivity reaction, commonly manifested by insidious onset of malaise, cough, dyspnea on exertion, altered ABGs.
  • Be alert for and advise the patient to report onset of muscle weakness, tingling, numbness, or other sensations. Peripheral neuropathy can be severe and irreversible. Drug should be withdrawn immediately.

Patient & Family Education

  • Be aware that IM injection of nitrofurantoin may be painful (pain may be severe enough to warrant discontinuation of drug by this route).
  • Nitrofurantoin may impart a harmless brown color to urine.
  • Consult physician regarding fluid intake. Generally, fluids are not forced; however, intake should be adequate.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 06/25/2022 (0)
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