What You Should Know About Nitrofurantoin Side Effects

Nitrofurantoin (brand names Macrobid and Macrodantin) is one of the most prescribed antibiotics for urinary tract infections in the United States. It's been around since the 1950s, it's effective, and it has some of the lowest bacterial resistance rates of any UTI antibiotic. But like all medications, it comes with potential side effects.

Most people tolerate Nitrofurantoin well, especially during the typical 5–7 day course for an acute UTI. However, understanding what's normal, what's not, and when to seek medical attention can help you feel more confident about your treatment.

What Is Nitrofurantoin? (Quick Overview)

Nitrofurantoin is a nitrofuran antibiotic used specifically for uncomplicated lower urinary tract infections (acute cystitis). It works by attacking bacteria through multiple mechanisms, which is why resistance rates remain low even after decades of use. It's available as generic capsules and under brand names like Macrobid (100 mg, twice daily) and Macrodantin (50–100 mg, four times daily).

Common Side Effects

These side effects are relatively frequent but usually mild. They often improve as your body adjusts to the medication or resolve once you finish your course:

• Nausea — The most commonly reported side effect. Taking Nitrofurantoin with food or milk significantly reduces nausea and also increases absorption by about 40%.
• Headache — Mild to moderate headaches may occur during treatment. Over-the-counter pain relievers like acetaminophen (Tylenol) are generally safe to take alongside Nitrofurantoin.
• Flatulence and gas — Some people experience bloating or increased gas.
• Diarrhea — Mild diarrhea is common with many antibiotics. Stay hydrated and contact your doctor if it becomes severe or bloody.
• Loss of appetite — You may not feel as hungry while taking the medication. Try eating smaller, more frequent meals.
• Vomiting — Less common than nausea but can occur, especially if taken on an empty stomach.
• Rust-yellow or brown urine — This is harmless and expected. Nitrofurantoin and its metabolites discolor urine. It's not a sign of a problem—it actually means the drug is concentrating in your urinary tract where it needs to work.

Tip: The single most important thing you can do to reduce common side effects is to always take Nitrofurantoin with food. This is not optional advice—it genuinely makes a difference.

Serious Side Effects

Serious side effects are uncommon, especially during a short course of treatment. However, they're important to know about so you can act quickly if something doesn't feel right.

Pulmonary Toxicity (Lung Problems)

This is the most clinically significant risk associated with Nitrofurantoin, particularly with long-term use (months to years of prophylactic therapy).

• Acute pulmonary reactions can occur within hours to weeks of starting the drug. Symptoms include sudden fever, chills, cough, chest pain, and difficulty breathing. This is typically reversible once the drug is stopped.
• Chronic pulmonary fibrosis can develop with long-term use (usually 6+ months). Symptoms include gradual onset of cough, shortness of breath, and reduced exercise tolerance. This may not be fully reversible.

When to call your doctor: Contact your doctor immediately if you develop a new cough, shortness of breath, chest pain, or fever while taking Nitrofurantoin.

Hepatotoxicity (Liver Problems)

Nitrofurantoin can cause liver damage, including cholestatic jaundice, hepatitis, and rarely hepatic necrosis.

• Symptoms include yellowing of the skin or eyes (jaundice), dark urine (beyond the normal discoloration), unusual fatigue, nausea, abdominal pain, or itching.
• Liver reactions can occur with both short-term and long-term use.

When to call your doctor: Stop taking Nitrofurantoin and contact your doctor right away if you notice yellowing of your skin or eyes, severe fatigue, or persistent abdominal pain.

Peripheral Neuropathy (Nerve Damage)

Numbness, tingling, or pain in the hands or feet can indicate peripheral neuropathy. This is more common with:

• Long-term use
• Impaired kidney function (which is why Nitrofurantoin is contraindicated when creatinine clearance is below 60 mL/min)
• Vitamin B deficiency, diabetes, or other conditions that affect nerves

When to call your doctor: Report any new numbness, tingling, or weakness in your extremities immediately. Nerve damage may be irreversible if the drug is not stopped promptly.

Hemolytic Anemia

Nitrofurantoin can cause red blood cells to break down, especially in people with G6PD deficiency (a genetic enzyme deficiency more common in people of African, Mediterranean, and Southeast Asian descent).

• Symptoms include unusual fatigue, pale skin, dark urine, rapid heartbeat, and shortness of breath.

When to call your doctor: If you experience signs of anemia (extreme fatigue, pallor, rapid heartbeat), seek medical attention promptly.

Other Serious but Rare Side Effects

• Optic neuritis — Changes in vision, eye pain
• Lupus-like syndrome — Joint pain, rash, fever
• Clostridium difficile-associated diarrhea (C. diff) — Severe, watery diarrhea that may occur during or after antibiotic treatment

Specific Populations: Who Needs Extra Caution?

Older Adults (65+)

Nitrofurantoin is on the Beers Criteria list of potentially inappropriate medications for older adults due to increased risk of pulmonary toxicity, liver damage, and peripheral neuropathy. If you're over 65, your doctor should carefully weigh the benefits against these risks, especially for long-term use.

Pregnant Women

Nitrofurantoin is generally considered safe in early pregnancy and is commonly prescribed for UTIs during the first and second trimesters. However, it is contraindicated at term (38–42 weeks) due to the risk of hemolytic anemia in the newborn.

People with Kidney Problems

If your creatinine clearance is below 60 mL/min, Nitrofurantoin should not be used. Reduced kidney function means the drug won't concentrate properly in the urine (making it less effective) and will accumulate in the blood (increasing toxicity risk). Your doctor should check kidney function before prescribing.

Breastfeeding Mothers

Nitrofurantoin passes into breast milk in small amounts. It's generally considered compatible with breastfeeding, but should be avoided if the infant is under 1 month old or has known G6PD deficiency.

How to Manage Common Side Effects

Here are practical strategies to minimize discomfort while taking Nitrofurantoin:

• Take every dose with food or milk. This is the single best way to reduce nausea, vomiting, and stomach upset while also improving how well the drug works.
• Stay hydrated. Drink plenty of water throughout the day to support urinary tract health and reduce GI side effects.
• Don't skip doses. Taking Nitrofurantoin at regular intervals keeps drug levels consistent. Skipping doses can reduce effectiveness and contribute to resistance.
• Complete the full course. Even if you feel better after 2–3 days, finish all prescribed doses. Stopping early increases the risk of the infection returning.
• Avoid antacids containing magnesium trisilicate. These can reduce Nitrofurantoin absorption. If you need an antacid, ask your pharmacist for an alternative.
• Don't be alarmed by urine color changes. Brown or rust-colored urine is a normal, harmless effect of the medication.

Final Thoughts

For the vast majority of people taking a short course of Nitrofurantoin for a UTI, side effects are mild and manageable—usually just some nausea that goes away when you take the medicine with food. The serious risks (lung, liver, nerve damage) are primarily associated with long-term use and are rare during a standard 5–7 day course.

The key is knowing what to watch for. If you develop breathing problems, yellowing skin, or numbness in your hands or feet, don't wait—call your doctor right away.

Need help finding Nitrofurantoin at a pharmacy near you? Medfinder can help you check availability. And if cost is a concern, check out our guide on how to save money on Nitrofurantoin.