Nitrofurantoin - Dosage, Uses, and Side Effects

Nitrofurantoin: An Overview

Nitrofurantoin is used to treat UTIs (urinary tract infections), especially infections in the bladder. Nitrofurantoin is a prescription medicine, which means you need a doctor’s prescription to get it. It is not available over-the-counter (OTC).

It has been approved by the FDA since 1953 and works by killing the germs that cause these infections. Nitrofurantoin stays mostly in the urine, so it works best for bladder infections but not for serious kidney problems.

Drug Group

Nitrofurantoin belongs to a drug class of broad-spectrum bactericidal antibiotics. Nitrofurantoin is an antibacterial (nitrofuran class) used mainly for urinary tract infections.

Indications or Uses

• Nitrofurantoin is a medicine used to treat UTIs (urinary tract infections), especially bladder infections.

• It works only against certain bacteria that cause these infections, like E. coli.

• Your doctor may do a urine test to make sure the bacteria will respond to this medicine.

• If a test isn’t available, doctors may use information about common local bacteria to choose treatment.

• Taking Nitrofurantoin the right way helps it keep working well and lowers the chance of bacteria becoming resistant.

Things to Keep in Mind

• Nitrofurantoin does not spread widely in body tissues like some other antibiotics.

• Because of this, some patients may still have bacteria in their urine even after treatment.

• Doctors sometimes use Nitrofurantoin because, even though it may not work as strongly as some other antibiotics, it is safer and less likely to cause resistance or serious side effects.

Dosage Forms and Available Strengths

• Capsules: You can find Nitrofurantoin macrocrystals in different strengths like 25 mg, 50 mg, and 100 mg. There’s also a 100 mg option that combines two forms of Nitrofurantoin monohydrate and macrocrystals, to help it work better for you.

• Oral Suspension: Nitrofurantoin oral suspension, typically 25 mg per 5 mL (strength may vary by brand).

• Tablets: Usually in 50 mg or 100 mg strengths.

What Are the Associated Warnings and Precautions?

• Use Only for Bacterial Infections: Nitrofurantoin treats only bacterial infections. It won’t help with any viral infection like the common cold.

• Complete Your Dose: Even if you feel better, keep taking the medicine as your doctor told you. Stopping early or missing doses can make the infection harder to treat and cause bacteria to become stronger against the medicine.

• Serious Side Effects: Diarrhea is commonly seen; however, some patients may develop severe diarrhea with watery or bloody stools, stomach cramps, or fever. This can happen even weeks after stopping the antibiotic. If this occurs, contact your doctor immediately.

• Avoid Unnecessary Use: Taking Nitrofurantoin when you don’t have a confirmed or likely bacterial infection probably won’t help you and can make bacteria stronger and harder to treat in the future.

For Patients

How Does Nitrofurantoin Work?

Nitrofurantoin is a medicine that kills germs (microorganisms) that cause urinary tract infections (UTIs). It stops them from growing, so your body can get rid of the infection. It stays mostly in the urine, which makes it especially effective for infections in the bladder and urinary tract.

Which Conditions Are Treated with Nitrofurantoin?

Nitrofurantoin is used for:

• Bladder infections (UTIs) are caused by certain bacteria.

• Preventing UTIs if you get them often.

Not used for:

• Kidney infections.

• Infections outside the bladder.

Nitrofurantoin Dosage Guidelines for Adults and Children

For Adults:

• Treatment of UTIs: 50–100 mg (macrocrystals) every 6 hours for 7 days or as directed.

• Prevention of UTIs: 50–100 mg once daily at bedtime.

For Children (Over 1 Month Old):

• Treatment of UTIs: 5–7 mg/kg/day, divided into 4 doses (maximum 400 mg/day).

• Prevention of UTIs: 1 mg/kg once daily at bedtime (maximum 100 mg/day).

How Is Nitrofurantoin Administered?

• It comes as a capsule, tablet, or liquid and is taken by mouth.

• Always take it with food or milk to help your body absorb it and avoid stomach upset.

• Capsule or tablet, swallow it whole with water. Don’t crush or chew it.

• If it is in liquid form, shake the bottle well before each dose. Use a measuring spoon or syringe, not a kitchen spoon.

• Take doses evenly spaced throughout the day so the medicine works best.

• It is necessary to finish all the medicine your doctor gives you, even if you feel better.

What Are the Side Effects of Nitrofurantoin?

Some side effects of Nitrofurantoin are mild and may go away on their own. Tell your doctor if they bother you or last long:

• Upset stomach (nausea, vomiting, heartburn, or gas).

• Loss of appetite.

• Headache.

• Hair loss.

Get medical help right away if you notice:

• Rash, hives, or itching.

• Trouble breathing or swallowing.

• Swelling of the face, lips, tongue, or throat.

• Fever, chills, chest pain, or a cough that doesn’t go away.

• Numbness, tingling, or weakness in hands or feet.

• Yellow skin or eyes, dark pee, tiredness, or pain under the ribs on your right side.

• Confusion, dizziness, or very pale skin.

• Severe diarrhea (watery or bloody), with or without fever and cramps, even up to 2 months after treatment.

• Eye pain or vision changes.

If you notice anything unusual, call your doctor.

What Are the Things to Inform the Doctor Before Taking Nitrofurantoin?

Before Taking Nitrofurantoin:

• Tell your doctor and pharmacist if you are allergic to Nitrofurantoin, any other medicines, or any ingredients in the capsules or suspension. You can ask for the ingredients to see what is in the medicine.

• Tell your doctor about all medicines, vitamins, herbs, or supplements you are taking or plan to take. Your doctor may change doses or watch for side effects.

• Let your doctor know if you take over-the-counter antacids, as these may interact with Nitrofurantoin. Do not start any new medicines without medical advice while on Nitrofurantoin.

• Tell your doctor if you have kidney disease, a history of jaundice, or liver problems from Nitrofurantoin; your doctor may advise against taking it.

• Tell your doctor if you have or have had anemia, diabetes, lung issues, nerve damage, electrolyte imbalance, vitamin B deficiency, or glucose-6-phosphate dehydrogenase (G6PD) deficiency.

• If you are pregnant, planning to be, or breastfeeding, tell your doctor. Nitrofurantoin should not be used in the last month of pregnancy because it can harm the baby.

Dietary Considerations

Keep eating your usual diet unless your doctor advises otherwise.

Missed Dose

If you forget a dose, take it right away unless it’s almost time for your next one. In that case, skip it and resume your usual schedule. Avoid taking two doses at once.

Overdose:

Signs of Nitrofurantoin overdose.

• Nausea, vomiting, or loss of appetite.

• Diarrhea.

• Dizziness, headache, or fatigue.

• Shortness of breath or chest discomfort.

• Cough or wheezing.

• Yellowing of the skin or eyes (jaundice).

• Numbness or tingling in hands or feet.

• Confusion.

What to Do?

• Seek emergency help immediately.

• Stop taking Nitrofurantoin.

• Supportive care in the hospital, doctors will monitor vital signs and provide fluids.

• Dialysis may be needed in very severe cases.

• There is no specific antidote, so prompt medical care is important.

Storage and Handling

• Keep this drug in its original container with the lid tightly closed. Make sure it is out of reach of children. Store it at room temperature, away from heat, moisture, and bathrooms.

• Throw away any unused medicine safely so kids, pets, or others cannot get it. Don’t flush it. Use a medicine take-back program and ask your pharmacist for local options.

• Always keep medicines out of children’s sight and reach. Lock safety caps and store them up high in a safe place.

For Doctors

Chemical Taxonomy

Chemical Name:

1-[[(5-NITRO-2-FURANYL)METHYLENE]AMINO]-2,4-IMIDAZOLIDINEDIONE

Chemical Type: Synthetic compound with controlled crystal size.

Appearance: Stable, yellow, crystalline powder.

What Are the Pharmacological Actions of Nitrofurantoin?

1. Pharmacodynamics and Mechanism of Action

• Nitrofurantoin is an antibacterial (nitrofuran class) used mainly for urinary tract infections.

• Its mechanism is unique: bacterial enzymes (flavoproteins) convert Nitrofurantoin into reactive compounds that damage bacterial proteins, DNA, RNA, and cell walls.

• This disruption blocks essential bacterial processes like protein synthesis and energy metabolism.

• Nitrofurantoin is bactericidal in urine at therapeutic doses.

• The complex mechanism explains why bacteria rarely develop resistance.

2. How the Body Handles the Medicine?

• Absorption Rate: The larger crystal form of Nitrofurantoin is absorbed slowly, but taking it with food improves absorption.

• Distribution: Blood levels are usually low at therapeutic doses.

• Excretion: Highly soluble in urine; may turn urine brown.

• Urinary Recovery: After 100 mg four times daily for seven days, about 36 to 38 percent is recovered in urine.

3. Interactions with Other Antibiotics:

Some in vitro antagonism with quinolones has been noted, though clinical significance is unclear.

4. Toxicity and Resistance

• Nitrofurantoin has had minimal resistance.

• Transferable or acquired resistance is extremely rare.

What Are the Contraindications of Nitrofurantoin?

• Kidney Problems: Do not use it if you have very low urine output (anuria or oliguria) or significant kidney impairment (creatinine clearance below 60 mL/min or high serum creatinine), as this increases the risk of toxicity.

• Pregnancy and Labor: Avoid pregnant women at term (38 to 42 weeks), during labor, or when labor is about to start due to the risk of hemolytic anemia in the baby.

• Newborns: Do not use it in infants under 1 month of age for the same reason.

• Liver Issues: Avoid if you have a history of liver problems or jaundice caused by Nitrofurantoin.

• Allergy: Do not use it if you are allergic to Nitrofurantoin.

What Are the Drug Interactions of Nitrofurantoin?

• Antacids: Antacids containing magnesium trisilicate can reduce the absorption of Nitrofurantoin, making it less effective.

• Uricosuric Drugs: Drugs like Probenecid and Sulfinpyrazone can reduce the kidney excretion of Nitrofurantoin. This may increase Nitrofurantoin levels in the blood (risk of toxicity) and reduce its effectiveness in the urine.

• Other Antibiotics: Some lab studies suggest Nitrofurantoin and Quinolone antibiotics may interfere with each other, but it’s not clear if this happens in real patients.

Which Clinical Studies Have Evaluated the Effectiveness and Safety of Nitrofurantoin?

Nitrofurantoin has been well studied for treating and preventing urinary tract infections (UTIs). The NCT00649506 study showed that taking it with food helps absorption. Research in PMC10361848 found it effective in women of all ages, including those with mild kidney problems. A review in Clinical Microbiology and Infection highlighted its role in preventing repeated UTIs. The JAMA Internal Medicine study confirmed that a 5-day course works well, giving high cure rates in a shorter time.

Use in Specific Populations:

Pregnancy:

• Category B. Animal studies show no major harm at normal doses.

• Avoid in the last month of pregnancy due to the risk of hemolytic anemia in the newborn.

• Use only if clearly needed.

Nursing Mothers:

• Small amounts pass into breast milk.

• Avoid infants under one month old due to potential serious side effects.

Pediatric Use:

• Contraindicated in infants less than one month old.

Geriatric Use:

Older adults may have a higher chance of lung or liver problems, especially with long-term use. Kidney function should be checked before and during treatment.

Conclusion:

Nitrofurantoin is a trusted antibiotic for treating and preventing urinary tract infections (UTIs), especially in the bladder. It works by killing bacteria and stopping them from spreading. When taken as prescribed, it has been safe for many years. Its special way of working makes resistance very rare. Overall, Nitrofurantoin is a reliable choice for treating and preventing repeated UTIs.

Note from iClinq:

• Nitrofurantoin kills bacteria in the urinary tract and stops them from spreading, making it effective for bladder infections.

• Nitrofurantoin has a unique mechanism that makes bacterial resistance very rare, keeping it effective even after decades of use.Clinical studies show that a 5-day course treats acute UTIs effectively, while long-term use can prevent recurrent infections.

• Consult our urologist if you notice persistent UTI symptoms, unusual side effects, or kidney-related concerns while taking Nitrofurantoin.