Nitrofurantoin: 7 things you should know
Medically reviewed by Carmen Fookes, BPharm. Last updated on Apr 16, 2020.
1. How it works
- Nitrofurantoin is an antibacterial agent with a large crystal structure (called a macrocrystal) which restricts absorption through the gastrointestinal tract allowing nitrofurantoin to concentrate in urine.
- Once in contact with bacteria, nitrofurantoin is broken down into its active components which inhibit several vital bacterial biochemical processes, such as protein and cell wall synthesis, DNA and RNA synthesis, and aerobic energy metabolism.
- Nitrofurantoin belongs to the class of medicines known as nitrofuran antibacterials.
- May be used as a treatment for urinary tract infections or at a lower dosage to reduce the recurrence of urinary tract infections.
- Nitrofurantoin is effective for treating certain gram-negative and gram-positive urinary tract infections, such as those due to Escherichia coli, Enterococci, Staphylococcus aureus and susceptible strains of Klebsiella and Enterobacter.
- Because nitrofurantoin concentrates in urine, side effects are generally less than with other agents typically used to treat urinary tract infections.
- Unlike many other antibiotics, resistance to nitrofurantoin has never been a significant problem; experts believe its broad spectrum of action offers a protective effect against resistance development. However, some bacteria are not susceptible to nitrofurantoin and care should still be taken not to encourage the development of resistant bacteria.
- Generic nitrofurantoin is available.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Nausea or vomiting, changes in facial skin color, dark colored urine, flatulence, headache and weight loss. Other side effects, such as abdominal pain, constipation, diarrhea, skin reactions, or cardiovascular effects are uncommon or relatively rare.
- Nitrofurantoin has been associated with potentially fatal lung conditions such as interstitial pneumonitis and pulmonary fibrosis. If these develop, nitrofurantoin should be discontinued. The risk is greater in people receiving nitrofurantoin for longer than six months.
- Not suitable for people with significantly impaired kidney function or in those with a previous history of liver problems associated with nitrofurantoin use.
- Should not be used in pregnant patients near term (38 to 42 weeks gestation) or when labor is imminent, or in newborns aged less than one month, because of the risk of hemolytic anemia.
- Because the distribution of nitrofurantoin to other tissues is limited, there is a higher chance that the bacterial infection being treated may persist or recur. Urine samples should be taken both before and after treatment.
- Should not be taken again by people who have had liver problems or reactions to nitrofurantoin in the past.
- May cause liver problems, particularly with long-term use. Periodic liver enzyme monitoring may be needed.
- Long-term use has also been associated with peripheral neuropathy (nerve disease or damage particularly confined to the feet or hands). The risk is greater in people with kidney disease, anemia, diabetes, electrolyte imbalance, vitamin B deficiency or with chronic debilitating diseases. Rarely, optic neuritis (inflammation of the optic nerve) may develop.
- May also cause other serious side effects such as hemolytic anemia (risk is greater in people with glucose-6-phosphate deficiency) and Clostridium difficile infection (symptoms include persistent diarrhea).
- May interact with quinolone antibiotics, and antacids that contain magnesium may reduce the absorption of nitrofurantoin. Probenecid and sulfinpyrazone can inhibit the excretion of nitrofurantoin, which may increase the risk of toxicity and decrease its effectiveness because this lowers the concentration of nitrofurantoin in the urinary tract.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- Take with food to enhance absorption and decrease the risk of side effects such as nausea.
- Take exactly as directed by your doctor. Ensure you finish the course as prescribed to decrease the risk of resistant bacteria developing.
- Do not take antacid or indigestion remedies containing magnesium trisilicate at the same time as taking nitrofurantoin.
- Nitrofurantoin should only be used to treat infections caused by susceptible bacteria; it does not treat infections caused by viruses. Do not share your nitrofurantoin with anybody else.
- Talk with your doctor if you start feeling unwell or develop shortness of breath on exertion, a cough that doesn't go away, or a numbness, tingling, or loss of sensation in your fingers or toes.
- Talk with your doctor if you develop watery or bloody stools with or without other symptoms such as stomach cramps or fever either while taking nitrofurantoin or within two months of discontinuing it.
- Do not take nitrofurantoin if you are in the last two to four weeks of your pregnancy.
- If using the oral suspension, shake well before use. Measure the exact dose and then swallow (may be mixed with water, milk or fruit juice before swallowing).
- Tell any health professional that treats you that you are taking nitrofurantoin as it may interfere with laboratory tests.
6. Response and Effectiveness
- The macrocrystalline form of nitrofurantoin allows nitrofurantoin to be absorbed more slowly, reducing any negative effects on the stomach (and decreasing the risk of nausea). An improvement in symptoms may be noticed within a couple of days; however, it is important the course of nitrofurantoin is finished or the drug continues to be taken for at least three days following a clear urine sample.
Medicines that interact with nitrofurantoin may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with nitrofurantoin. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may interact with nitrofurantoin include:
- antibiotics, such as chloramphenicol or tinidazole
- antifungals, such as fluconazole
- biologics, such as adalimumab, infliximab, or ipilimumab
- black cohosh
- cancer agents, such as paclitaxel, vinblastine, or vincristine
- HIV medications, such as efavirenz or stavudine
- magnesium salts
- medications to lower cholesterol, such as atorvastatin or fluvastatin
- peginterferon alfa and beta
- red yeast rice
- sodium nitrate
- vaccinations, such as BCG, cholera, or typhoid vaccine (may diminish the effectiveness).
Note that this list is not all-inclusive and includes only common medications that may interact with nitrofurantoin. You should refer to the prescribing information for nitrofurantoin for a complete list of interactions.
Nitrofurantoin. Revised 09/2019. Drugs.com https://www.drugs.com/ppa/nitrofurantoin.html
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use nitrofurantoin only for the indication prescribed.
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