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How Long Does Macrobid Stay In Your System? Should You Worry?

You or someone you know might be taking Macrobid. After all, this is a powerful antibiotic drug that physicians prescribe. But you might have the question, how long does Macrobid stay in your system? That’s what we’ll be talking about today.

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How Long Does Macrobid Stay In Your System?

It is quite difficult to say exactly how long a drug can stay in a person’s body. The reason is because of individual variation. Nevertheless, we can make estimates for the majority of the population.

For most people, Macrobid can stay up to 24 hours after the administered dose. But there’s a lot more to it than what meets the eye. The reason is that the active compound, nitrofurantoin, is eliminated very fast. It stays only for 4-5 hours.


But, in nitrofurantoin, the drug itself is given in different forms. So, it can stay longer, though you have nothing to worry about. Let’s dive a bit deeper into what exactly happens.

What Exactly Is Macrobid?

A quick google search will tell you that Macrobid is the name of a drug called nitrofurantoin. This is a urinary antiseptic drug. It means that it is used to treat infections of the lower urinary tract. It is available as a generic medication.

How Does It Work?

So, what is the way through which this drug works? As we’ve said, Nitrofurantoin is a urinary antiseptic. The bacteria infect the urinary bladder or the urethra. So, the drug has to reach there in order to act.

Most antibiotics reach their site of action through blood. But that’s not what happens in the case of nitrofurantoin. This drug is heavily excreted from the blood to your urine in the kidneys. Then, it can reach the urine and thus the bladder and the urethra.


The drug gets into the bacteria. Then, they destroy the bacterial components from the inside. The bacteria can’t make any new proteins and die eventually.

Uses of Macrobid

This is a drug mainly used to kill bacteria in the urinary tract. Some of the bacteria it can work against include:

  • Staphylococcus saprophyticus
  • Escherichia coli
  • Enterococcus faecalis
  • Bacillus subtilis
  • Klebsiella, Citrobacter, etc. species
However, this drug doesn’t stay in the blood for too long. That’s why it isn’t used for any other diseases.

Side Effects of Macrobid

This is a well-tolerated drug. But patients have observed some side effects occasionally. The most common side-effect is somnolence or drowsiness. Some other effects include-

  • Nausea
  • Vomiting
  • Headache
  • Drowsiness
  • Weakness
  • Brownish or discolored urine
These are not very common. And even if they do occur to you, then they’ll likely go away once you stop taking the drug. However, if they occur persistently or if they are severe, then you should contact your doctor immediately.

There are some very rare, but serious side effects that may be associated with this drug too. They are:

  • Difficulty in breathing
  • Sudden pain in the chest
  • Severe itching all over the body
  • Bloody diarrhea
  • High fever
Different people react differently to drugs. So, if you experience anything severe, contact your healthcare provider immediately.

Withdrawal Symptoms

So, are there any Macrobid withdrawal symptoms? The drug itself doesn’t cause any harmful effects if you stop taking it. In fact, like most antibiotics, this drug doesn’t affect the normal processes of your body.

However, that doesn’t mean that you should stop this drug early. Antibiotics have a certain regimen that needs to be followed. The reason is that the drug takes that time to kill all the bacteria.

Your symptoms of UTI can resolve within the first few days of taking the drug. You may then be tempted to stop taking the drug. But, this is a huge mistake. Just because there are no symptoms doesn’t mean that all the bacteria are dead.

If you stop the drug early, some bacteria might remain. And they can multiply and cause the disease once again. Furthermore, the bacteria which do survive become highly resistant. So, they’ll require much stronger drugs the next time around.

Macrobid Formulation and Duration of Action

Nitrofurantoin is available in a few different formulations. Macrobid is one of those. But, it’s not a single type of formulation. In fact, there are two different forms of nitrofurantoin inside the Macrobid capsule to make its effects last longer.
To better understand what happens, let’s take a look at what normally determines how long a drug will act.

Normal Metabolism, Elimination, and Duration of Action of a Drug

Normally when you take a drug orally, it has to go through a lot of obstacles to reach its desired location. These processes are the absorption and distribution of drugs.

Firstly, the drug has to be broken down into very small pieces inside your digestive tract. Large particles of drugs find it difficult to pass through the walls of the intestines. But small molecules are very well absorbed.

Then, the drug molecules have to go into the cells of the intestines and then to the blood. Different drugs use different mechanisms to get through. After reaching the blood, the drug can then pass to the whole body.


The drug freely moves around in the blood. However, the blood gets to the liver at one point. The cells of your liver are designed to break down and change chemical substances. This makes it easier to get rid of them.

Now you may be asking, why would the liver want to get rid of the helpful drugs? The thing is, your liver considers the drug to be a complex chemical substance. So, it breaks the drug down. This is known as drug metabolism.

After metabolism, the drug goes to the kidneys. The kidneys get rid of the drug through the urine.

All drugs don’t go through these processes at the same speed. Some drugs can be absorbed very fast, but they may be metabolized slowly. The rate of urinary excretion can be different too.

Thus, how long a drug stays in your system depends on the speed of these processes. So, if we can slow down any of these processes, we can increase how long a drug can stay in the system.

Scientists use the term ‘half life’ to describe the speed of these processes. Half-life is the time it takes for half of the drug to be inactivated. Normally it takes around 5-6 half-lives for a drug to be completely eliminated from the body.

What Does That Mean for Macrobid?

Now, let’s put all of these together to answer, how long does Macrobid stay in your system. Nitrofurantoin has a very small half-life. It is about twenty minutes. So, it’ll take 100-150 minutes or a maximum of three hours for nitrofurantoin to get out of your system.

But, this isn’t good. Because you’d need to take the drug at least 4 times or even more every day to effectively treat the infection. So the scientists figured out a way to increase the duration of action of Macrobid.

Macrobid contains two separate kinds of nitrofurantoin. They are nitrofurantoin macro crystals (25% of the drug) and nitrofurantoin monohydrate (75% of the drug).

Nitrofurantoin monohydrate is smaller and breaks down very fast inside the digestive tract. They are then absorbed and give the effect.

However, nitrofurantoin macrocrystals don’t dissolve as fast. Rather, they slowly release nitrofurantoin. This delays the absorption of the drug. Hence, it can maintain proper drug concentration for longer.

So, to answer your question, how long does Macrobid stay in your system, the answer is around 24 hours. Due to the delay in absorption, this drug can stay for longer despite the short half-life.


Now you know the answer to how long does Macrobid stays in your system. Normally, it is around 24 hours. However, if you do experience any side effects for longer, you should contact your doctor immediately.


How long do the effects of Macrobid last?

The effects of the drug Macrobid last for as long as it stays in your system. So, if you’re experiencing any side effects, it should go away within 24 hours of the last dose. However, in rare cases, they can last for longer in which case you should see a doctor.

Does nitrofurantoin work after you stop taking it?

No, nitrofurantoin will not work if you stop taking the drug. You should never stop a drug without consulting with your doctor first. If you experience any side effects, you should inform them. If you suddenly stop taking nitrofurantoin, your infection might not be cured completely. Furthermore, the bacteria can even develop resistance.

How long does it take nitrofurantoin to leave your system?

Nitrofurantoin takes around 4 or 5 hours to completely leave your system. It has a short elimination half-life of around 20 minutes.

However, Macrobid might stay in your system for about 24 hours after the last dose. The reason is that it contains slow-releasing nitrofurantoin microcrystals. They delay the absorption. So, the effects are prolonged.

How long does it take for Macrobid to clear up a UTI?

The Macrobid regimen may last from three to seven days in general. You may start to feel better within two to three days. But, you should continue to take the drug according to your physician’s instructions. Otherwise, bacteria may persist and develop resistance.

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