How Long Does Nitrofurantoin Take To Work On A UTI (And Why)?

How Long Does Nitrofurantoin Take To Work On A UTI (And Why)?

Exact Answer: Up to 7 days

Nitrofurantoin is an antibiotic medication that is specifically used to treat or prevent Urinary tract infections or UTI. It is a nitrofuran antibacterial class of medication that can not be used to treat other bacterial infections or viral infections as it helps kill pathogenic bacteria only in the kidneys, bladder, and urethra. Nitrofurantoin is consumed with food or milk as this increases its absorption in the body.

The dosage and duration of nitrofurantoin medication vary based on the patient’s medical condition and response towards therapy. Bodyweight is another important factor that is taken under consideration while prescribing nitrofurantoin to children. Some of the brand names of this medicine include Macrodantin, Furadantin, Macrobid, etc.


How Long Does Nitrofurantoin Take To Work On A UTI?

The dose and duration of nitrofurantoin medication are different for each person. For the full treatment of a UTI, it is recommended to consume the antibiotic for several days as prescribed without any missed dose in between. Improvements in UTI symptoms may be observed within a couple of days following first consumption, however, some doctors also suggest the continuation of treatment for at least 3 days following clear urine samples.

The strength of the medicine determines the amount of nitrofurantoin that one must consume. The medical condition of the patient and the associated symptoms mainly determine the total number of doses per day, the time gap between each dose, and the total time needed to treat the condition. Nitrofurantoin is used to treat two major categories of UTI:

  • Lower tract UTIs
  • Upper tract UTIs

Lower tract UTIs or also known as bladder infections are the most commonly occurring UTI. These infections are easy to treat with nitrofurantoin because of fewer complications. Upper tract UTIs or kidney infections are more serious and may develop from an untreated lower tract UTI.

For the prevention of UTI, nitrofurantoin can be taken as a capsule, suspension, or tablet with a strength of 50-100 mg every day at bedtime as prescribed by a medical professional. The same form and strength can be used to treat UTI, but it has to be consumed at an interval of 6 hours in between each dose for up to 7 days or more on average. For extended-release capsules, the medication must be taken every 12 hours for up to 7 days.

The symptoms of UTI start to disappear within 3 days of medication. Complete treatment can be obtained only after one has undergone full nitrofurantoin medication and it may sometimes take more than 7 days to treat the condition based on several factors.

In summary:

Dosage FormTime Needed
Oral7 days or more
Extended-release capsule7 days

Why Does Nitrofurantoin Take So Long To Work On A UTI?

Nitrofurantoin has a large crystal structure called the macrocrystal which helps its absorption only in the urinary tract. The structure also promotes the restriction of absorption in the gastrointestinal tract and other parts, thereby, allowing it to function only against UTIs. As the nitrofurantoin is in contact with the bacteria, it gets broken down into its active components.

The active components of the antibiotic act as the inhibitory agents of different biochemical processes occurring in bacteria. It inhibits the bacterial protein and cell wall synthesis, aerobic energy metabolism, and DNA and RNA synthesis, further leading to the death of the bacteria. The structure and mode of action of nitrofurantoin add up to the total time taken by it to work against UTI.

Nitrofurantoin can affect the gut of the patient in some cases as it may also kill some good bacteria along with pathogenic bacteria leading to an imbalance in the gut microbiome. One may experience discomfort for up to 2 weeks. It is recommended to consume probiotics in such a scenario.

To manage effectiveness, medical professionals sometimes suggest a combination of nitrofurantoin and other interactive drugs such as:

  • Biologics such as ipilimumab or infliximab
  • Cannabidiol
  • HIV medications
  • Black cohosh
  • Hydroxy chloroquine
  • Metronidazole
  • Disulfiram
  • Peginterferon alfa and beta


Nitrofurantoin is an FDA-approved urinary tract antibacterial medication used to prevent and treat UTIs. It works against two major categories of UTI called the lower tract UTI and upper tract UTI. However, it is mostly used to treat the lower tract kinds with fewer complications.

The medication takes up to 7 days or more to completely remove UTI symptoms. It has a slow mode of action because of its macrocrystalline structure that allows it to concentrate in the kidneys, bladder, and urethra.



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Hi! I'm Nidhi.

Here at the EHL, it's all about delicious, easy recipes for casual entertaining. So come and join me at the beach, relax and enjoy the food.

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