Macrocrystalline / Nitrofurantoin

Nitrofurantoin (macrocrystalline/monohydrate) is an antibiotic used specifically to treat bacterial infections in the urinary tract.

• Macrobid is indicated for the treatment of acute uncomplicated urinary tract infections (acute cystitis) caused by susceptible strains of Escherichia coli or Staphylococcus saprophyticus
• Nitrofurantoin Monohydrate/Macrocrystalline capsules are indicated for the treatment of acute uncomplicated urinary tract infections (acute cystitis) caused by susceptible strains of Escherichia coli or Staphylococcus saprophyticus
• Neither product is indicated for kidney infections (pyelonephritis) or abscesses around the kidney — a different antibiotic is needed for those
• These medications should only be used when the infection is proven or strongly suspected to be caused by bacteria that nitrofurantoin can kill

Nitrofurantoin works differently from most antibiotics. Bacteria absorb it and convert it into highly reactive compounds that attack multiple critical targets at once — disrupting how bacteria build proteins, generate energy, synthesize DNA and RNA, and construct their cell walls. Hitting so many processes simultaneously makes it very difficult for bacteria to develop resistance. At the concentrations it reaches in urine, it is bactericidal — meaning it kills the bacteria outright rather than just slowing their growth.

Because bacterial resistance requires many simultaneous mutations to develop, resistance to nitrofurantoin has remained very rare since the drug was introduced in 1953. There is also no known cross-resistance with other antibiotic classes such as sulfonamides.

These capsules are taken by mouth. Always take them with food — food increases the amount of drug your body absorbs by about 40%. The standard course for adults and children over 12 is twice a day (every 12 hours) for seven days; follow your prescriber's exact instructions.

• Do not skip doses or stop early, even if you feel better — completing the full course helps clear the infection and reduces antibiotic resistance
• If you miss a dose, take it as soon as you remember; if it is almost time for your next dose, skip the missed one and continue your regular schedule — do not double up

Most people tolerate nitrofurantoin well. The most commonly reported side effects include:

• Nausea (most common — taking it with food can help)
• Headache
• Gas (flatulence)
• Diarrhea or upset stomach
• Abdominal pain or constipation
• Dizziness or drowsiness
• Brown discoloration of urine (harmless)

Serious reactions are rare but require immediate attention: sudden or worsening shortness of breath, cough, or chest pain (lung reaction); yellowing of the skin or eyes (liver problem); numbness or tingling in the hands or feet (nerve damage); or severe diarrhea with blood or mucus (C. difficile infection). Stop the medication and call your doctor or seek care right away if any of these occur.

• Lung reactions: Acute, subacute, or chronic lung inflammation or scarring (pulmonary fibrosis) can occur. Chronic reactions develop slowly, usually in people on long-term treatment (six months or more), and may cause permanent lung damage. Symptoms include cough, shortness of breath, and general tiredness. This has contributed to deaths and requires immediate discontinuation of the drug.
• Liver damage: Serious liver reactions — including hepatitis and liver cell death — are rare but have been fatal. Seek care immediately if you develop jaundice (yellow skin or eyes), dark urine, or extreme fatigue.
• Nerve damage (peripheral neuropathy): Numbness, tingling, or weakness in the limbs can occur and may become permanent. The risk is higher in people with kidney problems, diabetes, anemia, or vitamin B deficiency.
• Hemolytic anemia: Breakdown of red blood cells can occur, particularly in people with G6PD deficiency. Unusual tiredness, pale skin, or jaundice are warning signs.
• C. difficile-associated diarrhea: Like all antibiotics, nitrofurantoin can disrupt the normal gut bacteria and allow C. difficile to overgrow, causing severe diarrhea. This can occur even weeks after finishing the antibiotic.

Nitrofurantoin has a few notable interactions to be aware of:

• Magnesium trisilicate antacids: These antacids bind to nitrofurantoin in the gut and reduce how much is absorbed — avoid taking them together
• Probenecid and sulfinpyrazone (uricosuric drugs): These medications block the kidneys from excreting nitrofurantoin into the urine, which can raise drug levels in the blood (increasing toxicity risk) while lowering levels in the urine (reducing its effectiveness against the UTI)
• Quinolone antibiotics (e.g., ciprofloxacin): Lab studies suggest these may work against each other; combined use is generally avoided, though the clinical impact is not fully established

Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.

• Kidney disease: Do not take this medication if your kidneys are significantly impaired (creatinine clearance under 60 mL/min) — the drug can accumulate to toxic levels and won't reach adequate concentrations in the urine to be effective
• Late pregnancy: This medication is contraindicated at 38–42 weeks of pregnancy, during labor and delivery, or when labor is imminent — it can cause a dangerous blood condition (hemolytic anemia) in the newborn
• Newborns: Not for use in infants under one month of age, due to the same risk of hemolytic anemia
• History of liver problems with nitrofurantoin: If you have ever had cholestatic jaundice or liver dysfunction caused by nitrofurantoin, do not take it again
• Allergy to nitrofurantoin: Do not take this drug if you have had a hypersensitivity (allergic) reaction to it before
• G6PD deficiency: A genetic enzyme deficiency more common in people of Black, Mediterranean, or Near-Eastern heritage — increases the risk of red blood cell breakdown (hemolytic anemia) with this drug
• Diabetes, anemia, nerve problems, or vitamin B deficiency: These conditions raise the risk of nerve damage (peripheral neuropathy) with nitrofurantoin — tell your doctor if any apply to you
• Children: Not approved for children 12 and under based on the supplied product labeling for these capsule formulations

Accidental overdose of nitrofurantoin has generally only caused vomiting. There is no specific antidote. The main approach is to encourage vomiting (if appropriate) and drink plenty of fluids to help the kidneys flush the drug out through the urine. Nitrofurantoin can be removed by dialysis if needed — contact Poison Control or seek emergency care if an overdose is suspected.

Nitrofurantoin is bactericidal (bacteria-killing) at the concentrations it reaches in urine at therapeutic doses. It disrupts multiple essential bacterial processes simultaneously — protein synthesis, DNA and RNA production, energy generation, and cell wall construction — making it highly effective against susceptible urinary pathogens. Because bacteria must mutate many targets at once to resist it, acquired resistance is very rare. It is not effective against Pseudomonas, most Proteus, or Serratia species.

Each nitrofurantoin monohydrate/macrocrystalline capsule contains two forms of the drug: 25% macrocrystalline nitrofurantoin, which dissolves and absorbs more slowly, and 75% nitrofurantoin monohydrate, which forms a gel in the gut and releases the drug gradually. This design helps extend the release and reduces stomach upset. Taking it with food increases absorption by roughly 40%.

Blood levels remain very low after an oral dose — the drug concentrates in the urine rather than the bloodstream, which is why it works for bladder infections but not for kidney or tissue infections. About 20–25% of each dose is excreted unchanged in the urine over 24 hours, and it can turn urine brown (a harmless effect).

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