• Antibiotics treat infection by either destroying bacterial cell walls or preventing bacteria from reproducing and spreading.
  • Antibiotics treat bacterial infections but some of them may also have anti-inflammatory properties that can help other types of illnesses.
  • Antibiotics start taking effect immediately, but you may not feel symptom relief for a few days as your immune system calms down.
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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:

  1. Antibiotics kill bacteria by rupturing bacterial cell walls.
  2. Antibiotics kill bacteria by preventing them from forming cell walls in the first place.
  3. Antibiotics prevent bacterial growth by destroying the essential proteins that they use to reproduce.

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 antibiotics include ciprofloxacin, tetracycline, and rifamycin.

Some antibiotics can both kill bacteria and prevent farther growth. It just depends on the dose you're prescribed as well as how far your bacterial infection has progressed.

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.

Certain antibiotics also have anti-inflammatory effects, which may be useful in treating inflammation caused by a viral infection. For example, researchers are investigating how the antibiotic azithromycin may help reduce inflammation, may also help COVID-19 patients.

However, Kaveh points out that, "We are still learning about this effect of antibiotics. Azithromycin is one of these antibiotics. It is possible that some of the reported success from azithromycin is from its anti-inflammatory effect."

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.

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 antibiotics treat COVID-19?

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.

Yet, figures from China show that a large percentage of patients with severe cases of COVID-19 receive antibiotics. But it's not the viral infection they're treating.

Often times it's a secondary bacterial infection that patients develop due to a weakened immune system. In a review of 247 hospitalized COVID-19 patients in China, the researchers found that 15% of survivors and 50% of those who died, acquired secondary bacterial infections.

COVID-19 isn't the only disease that causes dangerous secondary infections. During the 2009 influenza A (H1N1) pandemic, the CDC estimates that globally 151,700 - 575,400 people died. Around half of these deaths were due to secondary bacterial pneumonia.

So physicians may prescribe an antibiotic as a precautionary measure. "We do not yet have accurate tools for determining when an infection is bacterial or viral, and in those cases, an antibiotic may be given empirically if deemed appropriate by the physician," says Kaveh.

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.

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 re-occur, 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.

However, more research is needed so you should still complete the full course of antibiotics you're prescribed for an infection.

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