• Bacterial infections

Macrobid Generic Name & Formulations

General Description

Nitrofurantoin (as macrocrystals and monohydrate) 100mg; caps.

Pharmacological Class


How Supplied


How Supplied

Black and yellow capsules imprinted with “Macrobid” on one half and “52427-285” on the other.

Bottle of 100 capsules.


Store at controlled room temperature 15°C to 30°C (59°F to 86°F).


Mechanism of Action

The mechanism of the antimicrobial action of nitrofurantoin is unusual among antibacterials. Nitrofurantoin is reduced by bacterial flavoproteins to reactive intermediates which inactivate or alter bacterial ribosomal proteins and other macromolecules. As a result of such inactivations, the vital biochemical processes of protein synthesis, aerobic energy metabolism, DNA synthesis, RNA synthesis, and cell wall synthesis are inhibited.

Macrobid Indications


For the treatment of acute uncomplicated urinary tract infections (acute cystitis) caused by susceptible strains of Escherichia coli or Staphylococcus saprophyticus.

Limitations of Use

Not indicated for the treatment of pyelonephritis or perinephric abscesses.

Macrobid Dosage and Administration


Take with meals. 100mg every 12hrs for 7 days.


Adults and pediatric patients >12 years: 100mg every 12 hours for 7 days. Take with food.

Urine specimens for culture and susceptibility testing should be obtained before and after completion of therapy.

Nitrofurantoins lack the broader tissue distribution of other therapeutic agents approved for UTI. If persistence or reappearance of bacteriuria occurs after treatment with Macrobid, other therapeutic agents with broader tissue distribution should be selected.


Not established.


To enhance tolerance and improve drug absorption, Macrobid should be taken with food (ideally breakfast and dinner).

Macrobid Contraindications


Anuria, oliguria, CrCl <60mL/min. Neonates <1 month of age. Labor & delivery. Pregnancy at term. History of cholestatic jaundice/hepatic dysfunction associated with nitrofurantoin.

Macrobid Boxed Warnings

Not Applicable

Macrobid Warnings/Precautions


Not for treating pyelonephritis or perinephric abscesses. Discontinue if pulmonary reactions, hepatic disorders, or hemolysis occurs. Renal insufficiency; monitor (esp. in elderly). G6PD or Vit. B deficiency. Anemia. Diabetes. Electrolyte imbalance. Monitor renal function and pulmonary condition in long-term use. Debilitated. Pregnancy (Cat.B). Nursing mothers: not recommended.


Pulmonary Reactions

  • Acute, subacute or chronic pulmonary reactions have been observed with nitrofurantoin treatment.
  • Discontinue Macrobid if these reactions occur.
  • Rare pulmonary reactions: Diffuse interstitial pneumonitis, pulmonary fibrosis; generally occur in patients on therapy for 6 months or longer.
  • Patients on long-term therapy should be monitored closely.


  • Rare: Hepatitis, cholestatic jaundice, chronic active hepatitis, hepatic necrosis.
  • Fatalities have been reported.
  • Monitor periodically; if hepatitis occurs, discontinue Macrobid.


  • Peripheral neuropathy has occurred and fatalities have been reported.
  • Factors that enhance neuropathy: Renal impairment, anemia, diabetes, electrolyte imbalance, vitamin B deficiency.
  • Monitor patients on long-term therapy.

Hemolytic Anemia

  • Cases of hemolytic anemia of the primaquine-sensitivity type have been reported with the use of nitrofurantoin.
  • Discontinue Macrobid if hemolysis occurs; hemolysis ceases when the drug is withdrawn.

Clostridium difficile-Associated Diarrhea

  • CDAD has been reported with nearly all antibacterial agents; severity ranges from mild diarrhea to fatal colitis.
  • Consider CDAD in all patients who present with diarrhea following antibiotic use.
  • If suspected or confirmed, antibiotic use not directed against C. difficile may need to be discontinued.

Pregnancy Considerations

No adequate  and well-controlled studies in pregnant women. 

Contraindicated in pregnant patients at term (38 to 42 weeks gestation), during labor and delivery, or when the onset of labor is imminent because of the possibility of hemolytic anemia due to immature erythrocyte enzyme systems.

Nursing Mother Considerations

Nitrofurantoin has been detected in human breast milk in trace amounts. A decision should be made whether to discontinue nursing or discontinue the drug.

Pediatric Considerations

Contraindicated in infants <1 month old. Safety and effectiveness in pediatric patients <12 years old have not been established.

Geriatric Considerations

Clinical studies did not include a sufficient number of patients 65 years of age and older to determine response difference. Spontaneous reports suggest a higher incidence of pulmonary reactions in elderly patients due to a higher proportion of these patients receiving long-term therapy with nitrofurantoin. Severe hepatic reactions have also been reported in elderly patients.

It may be useful to monitor renal function in elderly patients.

Renal Impairment Considerations

Nitrofurantoin is substantially excreted by the kidney; risk of toxic reactions is increased in patients with impaired renal function.

Anuria, oliguria, or significant renal impairment (CrCl<60mL/min or clinically significant elevated serum creatinine) are contraindications.

It may be useful to monitor renal function in elderly patients.

Macrobid Pharmacokinetics


Bioavailability of nitrofurantoin is increased by ~40% when administered with food.


Up to 90% serum protein bound.


Hepatic. ~90% serum protein bound.


Renal. Half-life: 0.72–0.78 hours.

Macrobid Interactions


Reduced absorption by magnesium trisilicate. Uricosurics (eg, probenecid, sulfinpyrazone) may inhibit tubular secretion. May cause false (+) glucose test with Benedict's or Fehling's solution.

Macrobid Adverse Reactions

Adverse Reactions

Nausea, headache, flatulence, dizziness, alopecia; C. diff-associated diarrhea, pulmonary disorders, hepatic damage, hemolytic anemia, peripheral neuropathy (may be irreversible), anaphylaxis, blood dyscrasias; rare: exfoliative dermatitis, Stevens-Johnson syndrome, aplastic anemia.

Macrobid Clinical Trials

Clinical Trials

In controlled clinical trials comparing Macrobid 100mg every 12 hours and Macrodantin 50mg every 6 hours for the treatment of acute uncomplicated UTIs, approximately 75% microbiologic eradication of susceptible pathogens was observed in each treatment group.

Macrobid Note

Not Applicable

Macrobid Patient Counseling

Patient Counseling

Macrobid should be taken with food (ideally breakfast and dinner).

Complete the full course of therapy; skipping doses or not completing therapy may decrease the effectiveness of the treatment and increase the likelihood of drug-resistance bacteria. 

Do not use antacids containing magnesium trisilicate while taking Macrobid.

Diarrhea is common with antibiotics and usually ends with treatment. If watery, bloody stools develop even as late as 2 months after the last dose of antibiotic, contact a health care provider.

Nitrofurantoin may impart a brown color to urine.