What to Know About Nitrofurantoin

Oral Antibiotic Highly Effective in Treating Uncomplicated UTIs

In This Article

Nitrofurantoin is an oral antibiotic used to treat certain urinary tract infections (UTIs). The drug works by stopping the growth of bacteria and is used either to treat an active UTI or to prevent infection in those with recurrent UTIs.

Nitrofurantoin cannot treat viral or fungal infections. It should only be used when a bacteria is proven or strongly suspected of causing the UTI. The inappropriate use of nitrofurantoin can increase the risk of toxicity and antibiotic resistance.

Sold under various brand names and formulations (including Macrodantin, Macrobid, Furadantin, and others), nitrofurantoin is on the World Health Organization's List of Essential Medicines and is the most prescribed drug among pregnant women in the United States, according to a 2015 study in Obstetrics and Gynecology.

Uses

Nitrofurantoin has been in use since the 1950s and is approved by the U.S. Food and Drug Administration (FDA) for the treatment and prevention of bacterial UTIs, including acute cystitis.

The emerging global resistance to other antibiotic drugs, including fluoroquinolones and Bactrim (trimethoprim/sulfamethoxazole), has fueled an increased demand for underused antibiotics like nitrofurantoin.

Unlike other commonly prescribed antibiotics, nitrofurantoin has a low potential for drug resistance. That, combined with a high degree of effectiveness, make it an ideal first-line choice for treating uncomplicated UTIs.

According to the FDA prescribing guidelines, nitrofurantoin exhibits good activity against the following bacteria:

On the other hand, nitrofurantoin is not active against most strains of Proteus or Serratia bacterium or any Pseudomonas species. Additionally, some strains of Enterobacter and Klebsiella are resistant to nitrofurantoin. 

While nitrofurantoin is effective in treating bladder infections, it is less able to penetrate kidney tissues and should never be used to treat pyelonephritis (kidney infection) or perinephric abscesses (kidney abscesses caused by a urinary tract obstruction).

Before Taking

The biggest concern about taking any antibiotic is the risk of drug resistance. Because antibiotics tend to be overused or used incorrectly, pathogenic (disease-causing) bacteria can quickly develop resistance to some of the more commonly prescribed drugs.

Worse yet, some of these bacteria can be spread through communities, meaning that you may "pick up" a bacteria that are already resistant to one or several antibiotic drugs.

To avoid resistance, your doctor must first ensure that your UTI is caused by bacteria and not a virus or fungus This can be done by obtaining a urine sample and performing a bacterial culture and antibiotic susceptibility test (AST).

In the absence of testing, nitrofurantoin may be prescribed if you have recurrent UTIs or if there is a community outbreak of UTIs (as can sometimes happen in nursing homes or during foodborne E. coli outbreaks).

Do not hesitate to ask for a urine culture and antibiotic susceptibility test if you have recurrent UTIs despite treatment.

Results can take anywhere from one to three days to complete and cost between $40 to $100 on average. Most health insurance plans will cover some or all of the cost.

Precautions and Contraindications

Nitrofurantoin can be used in adults and children but should be avoided in newborns under one month due to the risk of hemolytic anemia. Hemolytic anemia is a disorder in which red blood cells are destroyed faster than they can be produced. 

The same risks limit its use in pregnancy. In fact, nitrofurantoin is contraindicated for use in pregnant women at term (38 to 42 weeks), during labor and delivery, or when the onset of labor is imminent. 

Because the drug is excreted mainly through the kidneys, nitrofurantoin should be avoided in people with severe kidney impairment (as measured either by a creatinine clearance of under 60 milliliters per minute or elevated serum creatinine levels).

Other Antibiotic Options

Depending on the results of your urine tests, nitrofurantoin may or may not be recommended. If nitrofurantoin is not an option, other first-line drugs include Bactrim or a broad-spectrum antibiotic known as fosfomycin. Augmentin (amoxicillin/clavulanic acid) and cephalosporin antibiotics such as Rocephin (ceftriaxone) or Suprax (cefixime) may also be used.

The FDA advises against the use of fluoroquinolones when other options are available due to the high rates of resistance and an increased risk of severe side effects.

Dosage

Nitrofurantoin is available in capsule form for adults and older children. There are several different formulations, each with different indications and/or uses:

  • Macrodantin and Furadantin are formulations made with nitrofurantoin macrocrystals and offered in 25-milligram (mg), 50-mg, and 100-mg capsules.
  • Macrobid is made with nitrofurantoin monohydrate and available in 100-mg capsules only.
  • Furadantin oral suspension is made for children in a 25-milligram-per-5-milliliter (25mg/5mL) formulation.

The manufacturer's recommended dose varies by age and body weight as well as whether the drug is being used therapeutically (as treatment) or prophylactically (as prevention).

All listed dosages are according to the drug manufacturer. Check your prescription and talk to your doctor to make sure you are taking the right dose for you

For adults and children over 12:

  • Macrodantin or Furadantin: 50 mg to 100 mg every six hours for seven consecutive days
  • Macrobid: 100 mg every 12 hours for seven days
  • UTI prophylaxis: Macrodantin or Furadantin 50 mg to 100 mg per day for up to 12 months

For children one month to 12 years of age:

  • Furadantin suspension: 5 to 7 mg per kilogram (mg/kg) per day, taken in four divided doses, for seven days
  • UTI prophylaxis: 1 to 2 mg/kg per day, taken in either a single or divided dose

If treatment failure occurs, increasing the dose or duration of therapy is rarely useful and may only increase the risk of drug toxicity and resistance.

How to Take and Store

Nitrofurantoin should be taken with food as it improves drug absorption. The oral suspension can also be mixed with fruit juice, milk, or formula to improve its taste.

To reduce the risk of drug resistance, it is important to take the antibiotics as prescribed—and to completion—even if you are feeling better. Stopping early or missing doses allows resistant bacteria to "escape" and proliferate, reducing the effectiveness of the antibiotic the next time around.

Nitrofurantoin is most effective if the doses are divided evenly throughout the day. If you have to dose every six hours, set an alarm clock to remind you. If a six-hourly dose is too difficult, ask your doctor for 12-hourly Macrobid.

Nitrofurantoin capsules and oral suspension can be stored at room temperature, ideally between 68 to 77 F (20 to 25 C). Keep the medicine in a dry cupboard away from heat and direct sunlight.

Side Effects

As with all medications, nitrofurantoin can cause side effects. Most are low-grade and rarely cause treatment discontinuation. Other side effects are potentially severe but most commonly occur with prolonged or ongoing treatment.

Common

The most common side effects of nitrofurantoin are:

  • Headaches
  • Nausea
  • Vomiting
  • Loss of appetite
  • Diarrhea

Some of these symptoms will resolve as your body adapts to treatment. Others may persist and require over-the-counter medications to alleviate nausea, headaches, or diarrhea. Taking nitrofurantoin with food can also help.

Nitrofurantoin can sometimes cause a darkening of the urine. This is harmless and not an indication of liver problems. Once treatment is stopped, the color will normalize.

Serious Side Effects

On rare occasion, a medical condition called pulmonary hypersensitivity reaction (PHR) has been known to occur. It is most often caused when nitrofurantoin is used for more than six months, although it can sometimes occur after two weeks.

In some cases, the reaction can turn deadly if the symptoms are not recognized and treated early. Symptoms include:

  • Fatigue
  • Malaise
  • Shortness of breath on exertion
  • Cough
  • Unintentional weight loss
  • Fever
  • Chills
  • Chest pain

In severe cases, PHR can cause severe pneumonitis (lung inflammation) and pulmonary fibrosis (scarring of the lungs).

Call your doctor if you experience chronic fatigue or are unable to catch your breath after normal activity while taking nitrofurantoin. This is especially true if there is fever, chills, a persistent cough, or chest pains.

Warning and Interactions

Nitrofurantoin should be used with caution in people with liver or kidney disease. Even if your liver and renal enzymes are borderline normal, the extended use of nitrofurantoin can cause significant and even severe impairment.

Kidney function should be measured in advance of treatment and monitored regularly if nitrofurantoin is used prophylactically. Liver function should also be monitored.

If kidney impairment or hepatitis develops while taking nitrofurantoin, treatment should be stopped immediately.

Interactions

While there are only a handful of drug interactions associated with nitrofurantoin, some may be significant enough to require an adjustment of treatment. Among the interactions of concern:

  • Antacids can reduce the rate and extent by which nitrofurantoin is absorbed in the intestines. Separating the doses may help, but it is usually best to avoid antacids during antibiotic treatment.
  • Gout medications, such as probenecid and sulfinpyrazone, can reduce the excretion of nitrofurantoin from the kidneys, leading to toxicity. A reduction in the nitrofurantoin dose may be required.
  • Hormonal birth control may be affected by antibiotics such as nitrofurantoin, reducing their efficacy and increasing the risk of pregnancy. Additional forms of contraception may be needed if taking hormonal contraceptives with nitrofurantoin.

Nitrofurantoin can also affect the results of urine glucose tests. Advise your doctor or lab personnel if you are scheduled to take this test while on nitrofurantoin.

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