Macrodantin Drug Interactions: What to Avoid and What to Tell Your Doctor

What You Need to Know About Macrodantin Drug Interactions

Before starting any new medication, it's important to understand how it interacts with other drugs, supplements, and foods you're already using. Macrodantin (Nitrofurantoin) is generally a well-tolerated antibiotic with fewer drug interactions than many other medications — but there are still some combinations you need to watch out for.

This guide covers the major and moderate drug interactions for Macrodantin so you can have an informed conversation with your doctor and pharmacist.

How Drug Interactions Work

Drug interactions happen when one substance changes the way another works in your body. This can happen in several ways:

• Reduced absorption: One drug prevents another from being properly absorbed in your stomach or intestines, making it less effective.
• Increased blood levels: One drug causes another to build up in your body to higher-than-expected levels, increasing the risk of side effects or toxicity.
• Reduced effectiveness: One drug cancels out or weakens the effect of another.
• Additive toxicity: Two drugs that affect the same organ (like the liver) can increase the risk of damage to that organ when taken together.

With Macrodantin specifically, the most important interactions involve drugs that affect its absorption, its concentration in urine (where it does its work), or that increase the risk of liver damage.

Major Drug Interactions

These interactions are the most clinically significant. You should avoid these combinations or discuss them carefully with your doctor:

Magnesium Trisilicate-Containing Antacids

Antacids that contain magnesium trisilicate can significantly reduce how much Nitrofurantoin your body absorbs. This means the drug may not reach effective levels in your urine, and your UTI may not clear up. If you need an antacid while taking Macrodantin, ask your pharmacist to recommend one that does not contain magnesium trisilicate.

Probenecid

Probenecid (used for gout) interferes with Macrodantin in a double-negative way: it increases Nitrofurantoin levels in your blood (raising toxicity risk) while simultaneously reducing the drug's concentration in your urine. Since Macrodantin only works in the urine, this combination makes the medication both less effective and more dangerous. This combination should generally be avoided.

Sulfinpyrazone

Sulfinpyrazone (another gout medication) has a similar effect to Probenecid — it can increase blood levels of Nitrofurantoin while decreasing urinary concentration. The same risks apply.

Pexidartinib (Turalio)

Pexidartinib is a medication used for certain tumors. Both Pexidartinib and Macrodantin can cause liver damage, and taking them together significantly increases the risk of hepatotoxicity. This combination should be avoided. If you're taking Pexidartinib and develop a UTI, your doctor should prescribe a different antibiotic.

Moderate Drug Interactions

These interactions are less severe but still worth discussing with your doctor:

Quinolone Antibiotics (Norfloxacin)

Nitrofurantoin may antagonize (work against) the antibacterial effect of quinolone antibiotics like Norfloxacin in the urinary tract. If your doctor is considering a quinolone antibiotic for your UTI, they should generally choose one or the other — not both. This doesn't apply to all quinolones equally, but it's something your prescriber should be aware of.

Live Vaccines (BCG)

Like most antibiotics, Macrodantin may reduce the effectiveness of live bacterial vaccines, specifically the BCG vaccine (used for tuberculosis and sometimes bladder cancer treatment). If you're scheduled to receive a live vaccine, let your healthcare provider know you're taking an antibiotic so they can adjust the timing if needed.

Diphenoxylate/Atropine (Lomotil)

Diphenoxylate/Atropine is an anti-diarrheal medication. It slows down your digestive tract, which can increase how much Nitrofurantoin your body absorbs. This could potentially raise blood levels and increase the risk of side effects. If you're experiencing diarrhea while on Macrodantin, talk to your doctor before using Lomotil — they may recommend a different approach.

Supplements and Over-the-Counter Products to Watch

While Macrodantin has relatively few interactions with supplements and OTC products, there are a few things to keep in mind:

Antacids

As mentioned above, antacids containing magnesium trisilicate should be avoided. Other antacids (calcium carbonate, aluminum hydroxide) don't have the same interaction, but it's still a good idea to separate them from your Macrodantin dose by at least two hours to be safe.

Cranberry Supplements

Cranberry juice and supplements are commonly used for UTI prevention. There's no known interaction with Macrodantin, and you can safely continue using cranberry products while taking the medication. Just don't rely on cranberry alone to treat an active UTI — it's not a substitute for antibiotics.

Probiotics

Probiotics are generally safe to take alongside Macrodantin and may even help reduce antibiotic-related digestive side effects like diarrhea. Space your probiotic dose a few hours apart from your antibiotic for the best results.

Iron Supplements

There's no established major interaction between Nitrofurantoin and iron supplements, but high-dose iron can cause stomach upset on its own. If you're taking both, taking them at different times of day may help reduce GI discomfort.

Food and Drink Interactions

Food

Unlike many medications, food is actually recommended with Macrodantin. Taking it with a meal improves absorption and significantly reduces nausea and stomach upset. There are no specific foods you need to avoid.

Alcohol

There is no direct chemical interaction between Nitrofurantoin and alcohol — unlike some antibiotics (like Metronidazole), Macrodantin won't cause a severe reaction if you drink. However, alcohol can:

• Worsen GI side effects like nausea and stomach upset
• Dehydrate you, which isn't ideal when you're fighting a UTI
• Impair your immune system's ability to fight the infection

Most doctors recommend avoiding or limiting alcohol while taking any antibiotic. It won't cause a dangerous reaction with Macrodantin, but it's not helping your recovery either.

What to Tell Your Doctor Before Starting Macrodantin

Before your doctor prescribes Macrodantin, make sure they know about:

• All medications you're currently taking — including prescription drugs, over-the-counter medications, and supplements. Pay special attention to gout medications (Probenecid, Sulfinpyrazone) and antacids.
• Liver or kidney problems — Macrodantin is contraindicated in severe kidney impairment (creatinine clearance below 30 mL/min) and in patients with a history of liver problems from Nitrofurantoin.
• G6PD deficiency — This genetic condition increases the risk of hemolytic anemia with Macrodantin.
• Pregnancy status — Macrodantin is generally safe during pregnancy but is contraindicated at term (38-42 weeks). See our comprehensive Macrodantin guide for details.
• Allergies — Especially any previous reactions to Nitrofurantoin or related medications.
• Other antibiotics you've recently taken — This helps your doctor choose the right treatment and avoid antagonistic combinations.

Your pharmacist is also an excellent resource. When you pick up your prescription, they'll check for interactions with your other medications. Don't hesitate to ask them if you have questions about combining Macrodantin with anything else you're taking.

For more information about Macrodantin's side effects and safety, read our side effects guide. To learn about the medication itself, see What Is Macrodantin?.

Final Thoughts

Macrodantin has relatively few drug interactions compared to many other antibiotics — which is one of its advantages. The most important interactions to be aware of involve gout medications (Probenecid, Sulfinpyrazone), certain antacids (magnesium trisilicate), and medications that increase liver toxicity risk (Pexidartinib).

The golden rule: always give your doctor and pharmacist a complete list of everything you're taking. They'll catch any potential interactions and help you take Macrodantin safely and effectively.

Need help finding Macrodantin at a pharmacy near you? Medfinder can help you check availability and compare prices.