Known brand names include Macrobid.
A urinary antibiotic capsule (Macrobid) for uncomplicated bladder infections caused by E. coli or Staphylococcus saprophyticus. It is not for kidney infections, and it can cause lung, liver, and nerve reactions.
Inside bacteria, enzymes called flavoproteins change nitrofurantoin into reactive pieces. These pieces damage the bacteria's ribosomes, the parts that make proteins, along with other large molecules. As a result, the bacteria can no longer make protein, DNA, or RNA, produce energy, or build their cell walls, and they die. Because it hits so many targets at once, bacteria rarely become resistant to it.
Each Macrobid capsule holds two forms of the drug: one dissolves slowly, and the other forms a gel in the stomach and gut that releases the drug over time. Very little stays in the blood, but about a quarter of each dose passes unchanged into the urine within a day, where it kills bacteria and may turn the urine brown. Taking it with food raises the amount absorbed by about 40%. Because the kidneys clear it, poor kidney function leads to higher blood levels and more toxicity, such as nerve damage, while use for months is linked to lung scarring.
Nitrofurantoin treats acute, uncomplicated urinary tract infections of the bladder, also called acute cystitis. It works against bladder infections caused by two common germs, E. coli and Staphylococcus saprophyticus. It is meant to kill the bacteria in the urine and clear the infection. Because it treats only bacterial infections, it does not help colds, flu, or other viral infections.
Adults and children older than 12 take the capsule by mouth with food. It is not used for kidney infections or for abscesses around the kidney, because the drug does not spread widely into body tissues. It is also not given to people with poor kidney function, to babies younger than 1 month, or at the end of pregnancy and during labor. Bacteria may linger or return in some people after treatment, and they then need a different antibiotic.
Nausea and headache are the most common complaints, followed by gas, diarrhea, upset stomach, and dizziness. The label treats lung reactions as the main serious risk: sudden fever, chills, cough, and shortness of breath in the first week, or slow lung scarring after six months or more of use, sometimes fatal. It also warns about liver injury, nerve damage in the hands and feet that can become permanent, breakdown of red blood cells in people with G6PD deficiency, and severe diarrhea from C. difficile.