December 2, 2022

How long does it take for an effective dose

  • The antibiotics start working immediately, but you may not feel symptom relief for a few days.
  • Antibiotics treat bacterial infections by destroying cell walls or preventing reproduction.
  • Some antibiotics may also have anti-inflammatory properties that can help other types of illnesses.
  • Visit Insider’s Health Reference Library for more tips.


are a popular group of drugs that help the body fight bacterial infections. In 2017, doctors alone wrote to Americans around 260 million antibiotic prescriptions, according to the Center for Disease Control.

Here’s what you need to know about this essential class of drugs.

How do antibiotics work?

Antibiotics treat bacterial infections in different ways that involve disrupting various parts of how bacteria survive and multiply in the human body.

Bacteria have cell walls that protect them from the harsh environment inside you. These cell walls protect the fragile interior that contains essential DNA and proteins that bacteria use to reproduce asexually. Antibiotics often work in one of three ways:

  1. Antibiotics kill bacteria by breaking down the bacteria’s protective cell walls or by preventing cell walls from forming in the first place.
  2. Antibiotics interfere with the bacteria’s ability to copy their DNA, which is necessary for reproduction.
  3. Antibiotics interfere with the metabolism of bacteria, making it difficult for them to multiply and spread throughout the body.

Bactericidal antibiotics are drugs that kill bacteria outright. Examples include penicillin, vancomycin and cephalosporin.

Bacteriostatic antibiotics are drugs that prevent bacteria from multiplying. Examples include ciprofloxacin, tetracyclineand rifamycin.

Some antibiotics can both kill bacteria and prevent additional growth. It just depends on the dose you are prescribed as well as the progress of your bacterial infection.

How long do antibiotics take to work?

Antibiotics start working almost immediately. For example, amoxicillin takes about one o’clock to reach peak levels in the body. However, a person may not feel relief from symptoms until later.

“Antibiotics typically show improvement in patients with bacterial infections within one to three days,” says Kaveh. This is because for many diseases, the body’s immune response is the cause of some of the symptoms, and the immune system may take time to calm down after the harmful bacteria have been destroyed.

Some antibiotics, such as fosfomycin which is used to treat certain cases of urinary tract infections, works immediately and usually only requires one dose. Other antibiotics, including tetracycline which is used to treat a wide range of conditions from acne to syphilis, may take several weeks of treatment with multiple doses before the patient notices an improvement in symptoms.

“The time frame depends on the type of infection and the sensitivity of the bacteria to that particular antibiotic,” says Kaveh.

What do antibiotics treat?

Doctors prescribe antibiotics for all types of bacterial infections, from minor strep throat or urinary tract infections to serious and life-threatening conditions such as bacterial infections.


or sepsis.

“The properties of some antibiotics also make them amenable to other medical conditions,” says Anthony Kave, MD, anesthesiologist and specialist in integrative medicine. For example, the quinolone and tetracycline groups of antibiotics are used in antimalarial therapy.

Some antibiotics also have anti-inflammatory effects, which can be helpful in treating inflammation caused by a viral infection. However, Kaveh points out that there is still research to be done on the anti-inflammatory effects of antibiotics.

What antibiotics should I take?

Depending on the type of infection, a doctor may prescribe one of two types of antibiotics: broad-spectrum or narrow-spectrum.

Broad-spectrum antibiotics affect a wide range of bacteria, whereas narrow spectrum antibiotics attack specific types of bacteria.

Doctors often try to prescribe narrow-spectrum antibiotics when they know which bacteria caused the infection. For example in pharyngitis caused by Streptococcus pyogenes, a doctor can prescribe benzylpenicillin.

Indeed, the unnecessary use of broad-spectrum antibiotics can contribute to

antibiotic resistance

. “Unfortunately, the side effects of antibiotics must be taken into account […]. In particular, bacterial resistance should be considered when using antibiotics for non-bacterial infections,” says Kaveh.

Can I stop taking antibiotics earlier?

It’s important to finish the full course of antibiotics, even if you start to feel better first.

Because if you stop treatment early, you risk not eliminating enough bacteria and the disease could return, as the surviving bacteria multiply. It also contributes to the growing problem of antibiotic resistance.

However, in the ongoing battle against antibiotic-resistant superbugs, researchers have begun to study the dosage amount. A growing body of evidence suggests that shorter diets of antibiotic treatment can be just as effective as the longer cures traditionally prescribed.

Further research is needed, so you should always follow the full antibiotic treatment you have been prescribed for an infection.

Insider’s Takeaways

Antibiotics work to cure bacterial infections by attacking the cell walls of a bacterium, interfering with its DNA to prevent reproduction, or attacking the metabolism to prevent it from spreading.

Once you have started a course of antibiotics they will start working almost immediately, although there may still be a delay in symptom relief. The length of treatment depends on your diagnosis and how the bacteria react to the antibiotic.

Your doctor will prescribe either broad-spectrum antibiotics, which treat a range of bacteria, or narrow-spectrum antibiotics, which target a specific type of bacteria. To prevent a recurrence of the infection, it is important to follow the full course of antibiotics prescribed for you.