When starting a new medication, it’s always essential to consider dosage. The medication won’t do its job if the dosage is too low. Too high, and you may experience unpleasant side effects or even an overdose. Your doctor can help you determine the best Nitrofurantoin dosage for you or your child. These are the most commonly prescribed dosages of nitrofurantoin based on age, infection, and other factors.
What is nitrofurantoin?
Nitrofurantoin is an FDA-approved antibiotic medication. Antibiotic means “against life.” Fortunately, the medications we call antibiotics mainly target microorganisms like bacteria and not our healthy cells. In the U.S., oral antibiotics (meaning they are taken by mouth as a tablet, capsule, or liquid), like nitrofurantoin, are only available from the pharmacy by prescription. Nitrofurantoin is the medication’s generic name; it may also be sold under the brand names Macrobid, Mactrodantin, and Furadantin.
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Indications for Use
Some antibiotics are used to treat a wide range of infections, but nitrofurantoin generally has a much smaller scope of use. Nitrofurantoin kills the bacteria that cause urethra infections, bladder, ureter, and kidneys. It does not work against infections in other body parts, such as the throat, lungs, or sinuses. Although the human reproductive tract is near the urinary tract, nitrofurantoin does not treat sexually transmitted infections (STIs) either.
Types of Nitrofurantoin Formulations
Typically, nitrofurantoin comes in three forms: liquid (oral suspension), capsules (macrocrystals), or dual-release capsules (macrocrystals-monohydrate). They usually come in 25 mg, 50 mg, 100 mg, or 25 mg/5 mL oral suspension dosages.
Importance of Proper Nitrofurantoin Dosage
As with any medication, taking the correct nitrofurantoin dose ensures optimal health solutions. If you take too low of a dose of antibiotics, the medication may not be strong enough to kill the bacteria in your body, causing the urinary tract infection. This might mean you don’t feel better or start to feel a bit better and then worsen again. There is even some evidence that “inappropriately low antibiotic dosing may be contributing to the increasing rate of antibiotic resistance.”
Antibiotic resistance typically occurs when bacteria become immune to certain antibiotic medications they used to be susceptible to. Infection with these bacteria becomes challenging and usually requires strong antibiotics with intense, unpleasant side effects to treat.
On the other hand, taking too high of a dose can also have serious consequences. All medications come with some risk of side effects. With antibiotics, the most common adverse effects affect the gastrointestinal tract and include nausea, diarrhea, and stomach pain.
These adverse reactions can become more pronounced at higher doses. Severe diarrhea can cause you to become dehydrated and make you feel worse when you already have an infection.
In addition to gastrointestinal distress, nitrofurantoin can also affect the liver and lungs. Sometimes, nitrofurantoin causes elevated liver enzymes without symptoms, but in some rare cases, it can result in hepatitis.
If you continue taking nitrofurantoin after developing drug-induced hepatitis, your condition may progress to acute liver failure or chronic hepatitis with cirrhosis (scarring of the liver).
Long-term use of nitrofurantoin can also cause pneumonia, lung disease, or pulmonary fibrosis. Loss of pulmonary function may be permanent even after you stop taking nitrofurantoin.
Nitrofurantoin Dosage Based on Infection Type
Nitrofurantoin is prescribed to kill a wide range of gram-negative and gram-positive bacteria that cause urinary tract infections. It can treat both active infections and prevent future ones from occurring.
Treating Urinary Tract Infections (UTIs)
The urinary system is divided into the lower tract, which includes the urethra and bladder, and the upper tract, which comprises the ureters and kidneys. Infections of the lower urinary tract are called cystitis. Infections of the upper urinary tract are called pyelonephritis.
Symptoms of UTIs most often include painful, difficult, urgent, or frequent urination, pain in the lower abdomen, and bloody or cloudy urine. More severe infections may also cause fever, chills, confusion, and more intense and wide-ranging pain throughout the abdomen and back.
UTIs are usually classified as uncomplicated or complicated.
Nitrofurantoin is usually prescribed to treat uncomplicated UTIs. For a UTI to be uncomplicated, it has to occur in the lower urinary tract of a woman with a fully competent immune system who is not pregnant, does not have a catheter in place, and is not running a fever.
Common bacteria cause uncomplicated UTIs. These are usually easy to treat and have a low risk of further complications.
Any urinary tract infection that occurs in a male patient, a pregnant patient, an immunocompromised patient, or a patient with a urinary catheter is considered complicated.
Doctors also classify UTIs as complicated if they cause a fever, involve the upper urinary tract, result in sepsis, or are caused by unusual bacteria or a kidney stone.
Complicated UTIs are more challenging to treat and have a higher risk of complications. Nitrofurantoin is not typically prescribed for complicated UTIs.
Preventing UTI Recurrence
UTIs are considered recurrent (rUTI) when a patient has 2 or more cases of cystitis in six months or 3 or more cases in 12 months. If behavioral and hygiene modifications are ineffective in preventing subsequent infections, doctors may turn to antibiotics, including nitrofurantoin.
There are usually three strategies for antibiotic treatment. If the UTIs occur after exposure to an identifiable trigger, such as sexual intercourse, you may be instructed to take a single dose of nitrofurantoin after exposure to prevent infections. Another method is to prescribe standby antibiotics that you can self-start at the first sign of an infection.
Doctors may consider continuous antibiotic prophylaxis if neither of these strategies is effective. In this case, you will take a dose of nitrofurantoin daily for an extended period.
This is not usually a life-long treatment, and you must undergo periodic reviews to determine whether it is in your best interest to continue antibiotic prophylaxis.
Nitrofurantoin for Other Bacterial Infections
Nitrofurantoin does not effectively treat infections that occur outside the renal system. This is because its half-life is too short to reach other systems of the body with enough potency to be therapeutic.
Nitrofurantoin Adult Dosage Guidelines
When prescribing an adult patient nitrofurantoin, doctors will consider factors such as age and infection severity.
Standard Adult Dosage
If you take nitrofurantoin capsules or oral suspension, you usually take 50 to 100 mg every 6 hours for at least one week. Sometimes, you may have to continue to take the medication for 3 days after your urine comes back negative for disease-causing bacteria. Extended-release capsules are taken in 100mg doses every 12 hours for 7 days.
Nitrofurantoin Dosage for Severe Infections
If you have a severe UTI, your doctor will probably prescribe you the 100 mg tablet or standard capsule 4 times a day.
Nitrofurantoin Extended Treatment Duration
Doctors will either prescribe 50 or 100 mg of nitrofurantoin once a day at bedtime for continuous antibiotic prophylaxis of recurrent UTIs. Generally, it is not recommended to prescribe nitrofurantoin for more than 6 months, as continued treatment increases the risk of lung damage.
Suppose your doctor determines the benefits of continuing nitrofurantoin treatment beyond six months outweigh the risks. In that case, they will provide information on recognizing signs of pulmonary damage, such as a persistent cough or shortness of breath.
Nitrofurantoin Dosage Adjustment for Elderly Patients
Older adults may have kidney problems that prevent them from processing drugs as quickly. As a result, it may take longer for them to clear the drug out of their system and increase the risk of side effects.
As a result, doctors may choose to start on a 50 mg dose to prevent drug levels from building up in their bodies.
Nitrofurantoin Pediatric Dosage Recommendations
Nitrofurantoin is also used to treat UTIs in children. The most accurate way to choose the correct dosage for a child is based on their weight.
Age-Related Dosage Considerations
Babies can be prescribed nitrofurantoin as young as one month old. Your child may be prescribed adult dosages as young as 12, depending on their weight. At 12, children can also start taking 100 mg dual-release capsules.
Pediatric Dosage for UTIs
Pediatric weight-based dosing for nitrofurantoin ranges from 5 to 7 mg per kg of body weight daily, not exceeding 400 mg/day. Pediatricians have developed a fixed dosing recommendation for different weight ranges to make things easier for parents.
These doses are usually administered as a liquid suspension:
- 12.5 mg 4 times per day for children 7 to 11 kg
- 25 mg 4 times per day for children 12 to 21 kg
- 37.5 mg 4 times per day for children 22 to 30 kg
- 50 mg 4 times per day for children 31 to 41 kg
- 50 to 100 mg 4 times per day for children 42 kg or more
If you know your child’s weight in pounds, you can divide it by 2.205 to get their approximate weight in kilograms.
Safety and Efficacy in Children
Nitrofurantoin should be given to a child under one-month-old. However, Macrodantin and its generic form have been proven safe and effective in children as young as one month and older. Macrobid and its generic forms have only been studied in children aged 12 and older and should not be prescribed for younger children.
Nitrofurantoin in Pregnancy
It is prevalent for women to develop UTIs during pregnancy, as the growing uterus sits directly on top of the bladder and may prevent urine from draining properly. Nitrofurantoin is generally considered safe for women during their first two trimesters. Still, doctors may prefer to prescribe an alternative antibiotic in the third trimester, especially when they reach term at 38 weeks of pregnancy. There is a slight chance that newborns may develop a problem with their red blood cells if nitrofurantoin is taken shortly before or during labor.
Recommended Dosage During Pregnancy
Untreated UTIs can turn into a kidney infection, which may trigger early labor and lead to low birth weight in your baby. Your doctor will want to treat your UTI quickly and effectively to prevent further complications. The most commonly recommended nitrofurantoin therapy for pregnant women is 100 mg dual-release capsules twice a day.
Safe Dosage for Nursing Mothers
Small amounts of nitrofurantoin may pass to your baby through your breastmilk, though it is unlikely to cause any side effects in a healthy baby. However, it is recommended that you only take nitrofurantoin for no more than a few weeks while breastfeeding. If you are considering continuous antibiotic prophylaxis with nitrofurantoin, consider exploring alternate options or discontinuing breastfeeding.
You should not take nitrofurantoin while breastfeeding if your baby has jaundice or a rare red blood cell condition called glucose-6-phosphate dehydrogenase deficiency. Contact your doctor if your baby develops an upset stomach, oral thrush, or stops eating well.
Nitrofurantoin Drug Interactions and Dosage
There are three drugs you should never take with nitrofurantoin: magnesium trisilicate, Probenecid, and sulfinpyrazone. Magnesium trisilicate will make nitrofurantoin less effective and may prolong your infection. On the other hand, Probenecid and sulfinpyrazone may prevent you from adequately processing nitrofurantoin. Instead, it builds up in your blood, which may cause harmful side effects. Reduced levels in your urine also make it less effective at treating your UTI.
When to See a Doctor
If you suspect a UTI, you will need an antibiotic like nitrofurantoin to get rid of it and prevent the infection from spreading. Antibiotics can only be acquired with a valid prescription from a licensed doctor. If you don’t have a primary physician or don’t have time to schedule an in-person appointment, you can schedule a telehealth appointment from your home at your convenience. A licensed physician will evaluate your symptoms and can direct you toward the appropriate next steps, including providing you with a prescription for nitrofurantoin.
Read next: What Can Nitrofurantoin Be Used to Treat?
Frequently Asked Questions
It depends on how you would describe “strong”—in terms of efficacy or the severity of side effects. Nitrofurantoin is more than 80% effective at curing infections while causing relatively few side effects.
A twice-daily dose of 100 mg of nitrofurantoin was shown to have a 93% microbiological cure rate after 7 days and a 90% cure rate after 5 days. Nitrofurantoin passes very quickly from the bloodstream to the urine, meaning the most potent concentration is passed directly to the source of the infection.
The highest single dose of nitrofurantoin is 100 mg at a time. The maximum daily dose is 400 mg.
Most treatment regimens require you to take nitrofurantoin for one week or until 3 days after your urine cultures come back clean. Sometimes, you may take nitrofurantoin for several weeks or months to prevent recurrent infections.
Like all medications, nitrofurantoin can cause side effects. Some of the most common, mild side effects include yeast infections, vomiting, nausea, stomach pain, loss of appetite, and diarrhea. You may also experience numbness or pain in your hands and feet, weakness, dizziness, headache, and drowsiness.
In rare cases, nitrofurantoin can cause lung, liver, and nervous system problems and damage red blood cells. Call your medical professional if you experience breathing difficulties, chest pain, yellowing of the skin or eyes, dark urine, extreme numbness or tingling, muscle weakness, severe fatigue, fever, or chills.