Nitrofurantoin is concentrated in the urine, leading to higher and more effective levels in the urinary tract than in other tissues or compartments. With a 100 mg oral dose, plasma levels are typically less than 1 µg/ml while in the urine it reaches 200 µg/ml.
The mechanism of action
is unique and complex. The drug works by damaging bacterial DNA, since its
reduced form is highly reactive. This is made possible by the rapid
reduction of nitrofurantoin inside the bacterial cell by flavoproteins (nitrofuran
reductase) to multiple reactive intermediates that attack ribosomal proteins,
DNA, respiration, pyruvate metabolism and other macromolecules
within the cell. Nitrofurantoin exerts greater effects on bacterial cells than
mammalian cells because bacterial cells activate the drug more rapidly. It is
not known which of the actions of nitrofurantoin is primarily responsible for
its bactericidal activity. The broad mechanism of action for this drug likely
is responsible for the low development of resistance to its effects, as the
drug affects many different processes important to the bacterial cell.
Current uses include the treatment of uncomplicated urinary tract infections (UTIs) and prophylaxis against UTIs in people prone to recurrent UTIs.
Increasing bacterial antibiotic resistance to other commonly used agents, such as fluoroquinolones and trimethoprim/sulfamethoxazole, has led to increased interest in using nitrofurantoin. The efficacy of nitrofurantoin in treating UTIs combined with a low rate of bacterial resistance to this agent makes it one of the first-line agents for treating uncomplicated UTIs as recommended by the Infectious Diseases Society of America and the European Society for Microbiology and Infectious Diseases.
Nitrofurantoin is not
recommended for the treatment of pyelonephritis, prostatitis, and
intra-abdominal abscess, because of extremely poor tissue penetration
and low blood levels.
Nitrofurantoin oral capsule may cause drowsiness. It may also cause other side effects.
More common side effects
The more common side effects of nitrofurantoin can include:
If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.
Serious side effects
Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.
Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.
Certain medicines should
not be used at or around the time of eating food or eating certain types of
food since interactions may occur. Using alcohol or tobacco with certain
medicines may also cause interactions to occur. Discuss with your healthcare
professional the use of your medicine with food, alcohol, or tobacco.
Take Nitrofurantoin as advised by your doctor. Do not take in larger amounts than advised. It is advised to take this medicine at the same time every day. Consult the doctor if you experience any undesirable effects. Do not stop taking the medicine without consulting your doctor.
Nitrofurantoin oral capsule comes with several warnings.
Nitrofurantoin can cause a severe allergic reaction. Symptoms can include:
If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 911 or go to the nearest emergency room.
Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal (cause death).
Warnings for people with certain health conditions
For people with kidney disease: If you have a history of kidney disease, you may not be able to clear nitrofurantoin from your body well. This could lead to a buildup of nitrofurantoin. This raises your risk of side effects.
For people with liver disease: You should not use nitrofurantoin. It can make your liver damage worse.
Warnings for other groups
For pregnant women: During weeks 0–37 of pregnancy, nitrofurantoin is a category B pregnancy drug. That means two things:
Talk to your doctor if you’re pregnant or plan to become pregnant. Animal studies do not always predict the way humans would respond.
Nitrofurantoin can cause red blood cell problems in a newborn. For this reason, women who are pregnant should not take this drug:
Call your doctor if you become pregnant while taking this drug.
For women who are breastfeeding: Nitrofurantoin may pass into breast milk and cause side effects in a child who is breastfed. Talk to your doctor about breastfeeding your child. You may need to decide whether to stop breastfeeding or stop taking this medication.
For seniors: The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This raises your risk of side effects. If you’re older than 65 years, nitrofurantoin may not be a good choice for you.
For children: Do not use any form of nitrofurantoin in
infants younger than 1 month. Macrodantin and its generic form are safe for use
in children older than 1 month. Macrobid and its generic form have not been
studied in children younger than 12 years of age. They should not be used in
this age group.