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Home » How Long Does Nitrofurantoin Take to Work? (5 Facts)

How Long Does Nitrofurantoin Take to Work? (5 Facts)

As a kidney doctor, I often encounter patients seeking answers to questions about urinary tract infections (UTIs) and the medications used to treat them. One common question is: How long does nitrofurantoin take to work? In this article, I will provide five key facts about nitrofurantoin, its efficacy, and how it works to treat UTIs.

The short answer:

Nitrofurantoin starts working within a few hours after the first dose and usually improves UTI symptoms within 24-48 hours. However, a complete 5-7 day course is necessary to ensure the infection is fully treated.

Key points in this article:

  1. Nitrofurantoin becomes concentrated in urine within 1 to 4 hours after intake.
  2. Your UTI symptoms typically improve as fast as a few hours after nitrofurantoin’s first dose.
  3. A complete 5-7 days course is required for nitrofurantoin to work for UTI.
  4. Taking nitrofurantoin with food makes it work better for UTIs.

Fact 1: Nitrofurantoin becomes concentrated in urine within 1 to 4 hours after intake.

Nitrofurantoin is an antibiotic that works by killing bacteria in the urinary tract.

After you take a nitrofurantoin dose, it gets absorbed into your bloodstream and filtered through your kidneys.

It quickly becomes concentrated in your urine within 1 to 4 hours after intake. This is important because the more concentrated the antibiotic in the urine, the more effective it is at killing the bacteria causing the UTI.

So, Nitrofurantoin can only take a couple of hours to start working for your UTI.

For example, One study found that most UTI symptoms improve within the first 24 hours of starting an antibiotic such as nitrofurantoin (reference).

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Fact 2: Your UTI symptoms typically improve as fast as a few hours after nitrofurantoin’s first dose.

As nitrofurantoin starts to work, the bacteria causing the infection begin to die off. This can significantly reduce your UTI symptoms, such as pain or burning during urination, frequent and urgent need to urinate, and cloudy or strong-smelling urine.

Many patients report feeling better within a few hours after taking the first nitrofurantoin dose, with continued improvement over the next 24-48 hours.

For example, One study found that most UTI symptoms improve within the first 24 hours of starting an antibiotic such as nitrofurantoin (reference).

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It is essential to remember that even if your symptoms improve quickly, you must still complete the full course of the prescribed antibiotic to ensure the infection is entirely eradicated.

Stopping the medication too soon can lead to a relapse or the development of antibiotic-resistant bacteria.

Fact 3: A complete 5-7 days course is required for nitrofurantoin to work for UTI.

For nitrofurantoin to effectively treat a UTI, you must take the medication for the full course prescribed by your doctor, which is typically 5-7 days (reference).

It is crucial not to skip doses or stop taking the medication before the full course is completed, even if you start feeling better.

Completing the treatment ensures that all the bacteria causing the infection are killed, preventing the infection from returning or developing antibiotic-resistant bacteria.

The typical dosing may vary according to gender, severity, and age. The table below illustrates the typical dosing and duration of nitrofurantoin in UTI.

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FormulationDoseFrequencyDuration
Macrobid®100 mgTwice daily5 days (women) / 7 days (men)
Macrodantin®50-100 mgEvery 6 hours5 days (women) / 7 days (men)

In some cases, if your symptoms do not improve within 48 hours or worsen, you should contact your doctor, as a different antibiotic may be required to treat the infection.

Fact 4: Taking nitrofurantoin with food makes it work better for UTIs.

Nitrofurantoin is more effectively absorbed by the body when taken with food (reference).

This means that taking the medication with a meal or snack can help it work better and longer. Additionally, taking nitrofurantoin with food can help reduce the risk of stomach upset, a common side effect of the medication.

Drinking plenty of water while taking nitrofurantoin is also important, as staying well-hydrated helps flush the urinary tract and aids in the medication’s efficacy.

Fact 5: Nitrofurantoin is ineffective against all types of bacteria causing UTIs.

While nitrofurantoin is an effective treatment for many UTIs, it is not active against all types of bacteria that can cause urinary tract infections.

For example, nitrofurantoin is ineffective against Pseudomonas aeruginosa, a common cause of complicated UTIs.

Before prescribing nitrofurantoin, your doctor may perform a urine culture to identify the specific bacteria causing your infection, ensuring that the medication will effectively treat your UTI.

In cases where nitrofurantoin is not the best choice, alternative antibiotics, such as trimethoprim-sulfamethoxazole or fluoroquinolones, may be prescribed.