Antibiotics treat infections by killing or sterilizing bacteria right after the first dose
- Antibiotics start taking effect immediately, but you may not feel symptom relief for a few days.
- Antibiotics treat bacterial infections by either destroying cell walls or preventing reproduction.
- Some antibiotics may also have anti-inflammatory properties that can help other types of illnesses.
Antibiotics are a popular group of medicines that help the body fight bacterial infections. In 2017, alone, physicians wrote 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 medication.
How do antibiotics work?
Antibiotics treat bacterial infections in a few different ways that involve disrupting various parts of the way bacteria survive and multiply in the human body.
Bacteria have cell walls that help protect them against the harsh environment inside you. These cell walls protect the fragile interior that contains the DNA and essential proteins that bacteria use to reproduce asexually. Antibiotics often work in one of three ways:
- Antibiotics kill bacteria by rupturing the bacteria's protective cell walls or by preventing the cell walls from forming in the first place.
- Antibiotics interfere with bacteria's ability to copy their DNA, which is necessary for reproduction.
- Antibiotics interfere with bacteria's metabolism, which makes it difficult for it 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, tetracycline, and rifamycin.
Some antibiotics can both kill bacteria and prevent further growth. It just depends on the dose you're prescribed as well as how far your bacterial infection has progressed.
How long do antibiotics take to work?
Antibiotics start working almost immediately. For example, amoxicillin takes about one hour to reach peak levels in the body. However, a person may not feel symptom relief until later.
"Antibiotics will typically show improvement in patients with bacterial infections within one to three days," says Kaveh. This is because for many illnesses the body's immune response is what causes some of the symptoms, and it can take time for the immune system to calm down after the harmful bacteria are destroyed.
Some antibiotics, such as fosfomycin that's used to treat certain cases of UTIs, work immediately and usually only require one dose. Other antibiotics, including tetracycline that's 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 any improvement in symptoms.
"The timeframe depends on the type of infection and whether the bacteria are susceptible 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 severe, life-threatening conditions such as bacterial pneumonia or sepsis.
"The properties of some antibiotics make them amenable to other medical conditions, as well," says Anthony Kaveh, MD, physician anesthesiologist, and integrative medicine specialist. For example, the quinolone and tetracycline groups of antibiotics are used in anti-malarial therapy.
Important: Scientists agree that antibiotics don't directly affect SARS-CoV-2, the virus responsible for COVID-19. That's because "antibiotics do not treat viral infections," says Kaveh.
Certain antibiotics also have anti-inflammatory effects, which may be useful in treating inflammation caused by a viral infection. However, Kaveh points out that there is still more research to be done about the anti-inflammatory effects of antibiotics.
What antibiotics should I take?
Depending on the type of infection, a physician may prescribe you 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.
Physicians will often times try to prescribe narrow-spectrum antibiotics when they know which bacteria caused the infection. For example in pharyngitis caused by Streptococcus pyogenes, a physician may prescribe benzylpenicillin.
This is because using broad-spectrum antibiotics unnecessarily can contribute to antibiotic resistance. "Unfortunately, the side effects of antibiotics must be taken into account [...]. In particular, bacterial resistance must be considered whenever using antibiotics for non-bacterial infections," says Kaveh.
Can I stop taking antibiotics early?
It's important to complete the full course of antibiotics, even if you begin to feel better beforehand.
Because if you discontinue the treatment early you may not eliminate enough bacteria, and the condition could reoccur, as surviving bacteria multiply. Doing so also contributes to the growing issue of antibiotic resistance.
However, in the continued battle against antibiotic-resistant superbugs, researchers have started to study the dosage amount. A growing body of evidence suggests that shorter regimes of antibiotic treatment may be just as effective as the longer courses traditionally prescribed.
More research is needed, so you should still complete the full course of antibiotics you're prescribed for an infection.
Insider's takeaway
Antibiotics work to cure bacterial infections by either attacking a bacteria's cell walls, interfering with its DNA to prevent reproduction, or honing in on the metabolism to stop it from spreading.
Once you start a course of antibiotics, they will start working almost immediately, though there may still be a delay in symptom relief. The time frame 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's important to complete the full course of antibiotics that you're prescribed.