Nitrofurantoin is an antibiotic used to treat and prevent urinary tract infections (UTIs). It works specifically in the urinary tract and is one of the most commonly prescribed first-line treatments for uncomplicated bladder infections. You may recognize it by its brand names, Macrobid or Macrodantin.
Treating Bladder Infections
Nitrofurantoin’s primary use is treating uncomplicated lower urinary tract infections, meaning infections in the bladder and urethra. It’s not used for kidney infections or infections elsewhere in the body because the drug concentrates almost entirely in urine rather than building up in the bloodstream or other tissues. That narrow focus is actually one of its strengths: it reaches high concentrations right where the infection lives.
The antibiotic is effective against E. coli, the bacterium responsible for the vast majority of UTIs. It also works against several other common UTI-causing bacteria, including Staphylococcus saprophyticus and Enterococcus faecalis. However, it does not work against Proteus, Serratia, or Pseudomonas species, so if your UTI is caused by one of these, your provider will choose a different antibiotic.
A typical treatment course for a bladder infection is 5 to 7 days. The two main formulations are dosed differently: the monohydrate/macrocrystal version (Macrobid) is taken twice a day, while the macrocrystal version (Macrodantin) is taken four times a day. Taking it with food helps your body absorb the drug and reduces the chance of an upset stomach.
Preventing Recurrent UTIs
Beyond treating active infections, nitrofurantoin is widely used as a preventive medication for people who get UTIs repeatedly. The typical preventive dose is 50 to 100 mg taken once daily at bedtime, and this regimen can continue for several months. For some people, a single dose of 50 to 100 mg can also be taken after a known trigger, such as sexual intercourse, to head off an infection before it starts.
Nitrofurantoin tends to perform well in this preventive role partly because bacteria are slow to develop resistance to it. In studies comparing it to another common UTI antibiotic (trimethoprim-sulfamethoxazole, often called Bactrim), only about 37.5% of bacteria showed resistance to nitrofurantoin, compared with 56% resistance to Bactrim. That lower resistance rate makes nitrofurantoin a particularly reliable long-term option.
Why Resistance Stays Low
Unlike many antibiotics that target a single step in bacterial growth, nitrofurantoin attacks bacteria through multiple mechanisms at once. Inside bacterial cells, the drug is converted into reactive compounds that damage DNA, disrupt protein production, and interfere with energy metabolism simultaneously. Because a bacterium would need to develop defenses against all of these pathways at the same time, resistance evolves much more slowly than it does with antibiotics that have a single target. This is a meaningful advantage at a time when antibiotic resistance is a growing concern worldwide.
Who Should Not Take It
Because nitrofurantoin is cleared through the kidneys, it doesn’t work properly if kidney function is significantly reduced. The drug is contraindicated when estimated kidney filtration rate (eGFR) falls below 45 ml/min. Below that threshold, not enough of the drug reaches the urine to fight the infection, and the risk of side effects increases because more of it stays in the bloodstream. In certain cases, a short course of 3 to 7 days may still be considered for patients with an eGFR between 30 and 44, but only when dealing with multidrug-resistant bacteria and no better options exist.
Regarding pregnancy, guidance has been somewhat cautious. The American College of Obstetricians and Gynecologists has not given firm recommendations about using nitrofurantoin in the first trimester due to earlier uncertainty about birth defects. However, a large cohort study published in JAMA Network Open found no elevated risk of congenital malformations associated with nitrofurantoin use. It is generally avoided near the end of pregnancy and during labor because of a theoretical risk of breaking down red blood cells in the newborn.
Common and Serious Side Effects
Most people tolerate nitrofurantoin well, especially during short courses. The most frequent side effects are nausea, headache, and gas. Taking the medication with food significantly reduces stomach-related symptoms.
Lung reactions are the most important rare side effect to know about. An acute reaction can develop within the first week or two, causing fever, chills, cough, chest pain, and difficulty breathing. This type usually resolves once the drug is stopped. A chronic form can develop with long-term use over months, presenting as a lingering cough, shortness of breath, or coughing up blood or mucus. If you experience any breathing difficulties while taking nitrofurantoin, that warrants prompt medical attention.
Liver reactions are another rare but serious concern. Signs include yellowing of the skin or eyes, dark urine, pale stools, upper right abdominal pain, or itching. These can range from temporary inflammation to more severe liver damage, and they are more likely with prolonged use.
For people taking nitrofurantoin as long-term prevention, periodic monitoring of lung and liver function is standard practice to catch any problems early.
How It Compares to Other UTI Antibiotics
Nitrofurantoin occupies a specific niche. It is a first-line choice for uncomplicated bladder infections alongside trimethoprim-sulfamethoxazole and fosfomycin. Its advantages are low resistance rates, minimal disruption to the body’s normal bacterial communities (since it concentrates in the urine rather than spreading systemically), and decades of reliable use. Its limitations are equally clear: it cannot treat kidney infections, bloodstream infections, or UTIs caused by resistant organisms like Pseudomonas. If your infection involves fever, back pain, or other signs that it has spread beyond the bladder, a different antibiotic with broader tissue penetration will be needed.