How long does nitrofurantoin take to work on a UTI?

A urinary tract infection (UTI) results from bacteria entering your urethra. Because they’re due to bacteria, doctors treat UTIs with antibiotics.

Nitrofurantoin is a common, generic antibiotic that you might take over the course of several days. You can expect to feel better within a few days of taking nitrofurantoin, but you should finish your entire course of antibiotics.

If you have a complicated UTI, a doctor might recommend a longer antibiotic course and other treatments like fluid therapy. 

Sex and gender exist on spectrums. This article uses the terms “women,” “men,” or both when discussing people assigned female or male at birth to reflect language that appears in source materials. 

While gender is solely about how you identify yourself, independent of your physical body, you may need to consider how your personal circumstances will affect diagnosis, symptoms, and treatment. Learn more about the difference between sex and gender here.

How long does it take to work? 

Nitrofurantoin (Macrobid) should start to work within a few days. Even if you feel better, you should continue to take the medication until your prescription is complete.

This medication comes in a capsule or liquid form. A typical dosing schedule is 2–4 times every day for 5–7 days. 

These timelines generally apply to an uncomplicated UTI, which is the term for a UTI that affects the lower urinary tract and is less likely to lead to serious complications. A complicated UTI affects the upper urinary tract, such as the kidneys, and can cause more severe symptoms and complications. They may be harder to treat.

A complicated UTI might require a longer course of antibiotics, up to 10–14 days. You should be able to see if you are responding to treatment for a complicated UTI within 24–48 hours.  

Other treatments besides antibiotics for a complicated UTI include in-hospital fluid therapy.

Many factors can make your UTI complicated, such as if you are:

• immunocompromised
• pregnant
• male
• older
• living with kidney conditions

Men or people with penises might have to take an antibiotic course for a UTI longer than women or people without penises because the bacteria can go into the prostate gland.

In order to improve the effectiveness of nitrofurantoin and to help prevent antibiotic resistance, doctors recommend taking your dose at about the same time every day and avoiding skipping doses. 

Nitrofurantoin works by killing and stopping the growth of bacteria. It is an older antibiotic. It received Food and Drug Administration (FDA) approval to treat UTIs in 1953. Although it is possible to develop antibiotic resistance to nitrofurantoin, this is less common than with other antibiotics.

There are a few tips to follow to take antibiotics safely:

• take the course of nitrofurantoin as a doctor prescribes
• don’t share the antibiotic or take someone else’s prescription of nitrofurantoin
• don’t keep old antibiotics, but return unused antibiotics to a pharmacy for proper disposal.

To help your healing from a UTI, consider:

• drinking plenty of water
• urinating often and fully emptying your bladder
• using a heating pad to manage back or abdominal pain

Possible side effects

Some common side effects you might experience include:

• loss of appetite
• nausea or vomiting
• hair loss
• headaches
• gas or heartburn

If these side effects don’t go away or are severe, you might want to discuss them with a doctor.

Some uncommon and more serious side effects include:

• rash or hives
• problems swallowing or breathing
• flu-like symptoms
• numbness or tingling in fingers or toes
• muscle weakness
• yellowing of the eyes
• pain in the upper right area of your stomach
• confusion or dizziness
• vision changes
• severe diarrhea

If you have any of these more serious symptoms, consider seeing a doctor right away or visiting an emergency room.

Alternative medications 

Antibiotics are the first-line treatment for UTIs. A doctor might prescribe an alternative antibiotic to nitrofurantoin. Options might include:

• trimethoprim-sulfamethoxazole (Bactrim)
• fosfomycin (Monurol)

A 2021 research review of randomized controlled trials found that nitrofurantoin was at least as effective at treating UTIs as other kinds of antibiotics.

If you are hospitalized for a complicated UTI, a doctor might try different antibiotics in addition to other treatments. Broad-spectrum antibiotics that are effective against many different kinds of bacteria may also be useful if the initial antibiotic does not work.

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Summary

Nitrofurantoin is an antibiotic that can help treat your UTI. It usually gets to work within a few days, but you are likely to take a course of it for at least a week.

It works by killing bacteria. If you have serious side effects like hives, facial swelling, numbness or tingling, or yellowing of the eyes, contact a doctor immediately.

You can help manage a UTI by drinking plenty of water and urinating frequently. An antibiotic should always be taken as your doctor instructs. 

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