How Long Does It Take For Amoxicillin To Work?

In our latest question and answer, the pharmacist discusses how quickly amoxicillin begins to work.


How long does it take for amoxicillin to start working? I have a sinus infection.

Asked by Mary On Aug 15, 2021

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Aug 15, 2021
Last updated Aug 12, 2022

Key points

  • Symptom improvement after starting amoxicillin, a broad spectrum aminopenicillin antibiotic, is generally seen within 2 to 3 days.
  • If you do not start to feel better after a few days of amoxicillin therapy, it is important that you reach out to your provider.

Thank you for your question!

Amoxicillin is one of the most commonly prescribed antibiotics for the treatment of a sinus infection, also known as sinusitis.

It is an "aminopenicillin" antibiotic, similar to penicillin, but has a broader spectrum of activity, meaning it covers more types of bacteria.

How Does Amoxicillin Work?

After starting therapy, amoxicillin will begin to work faster than many other antibiotics since it is "bactericidal", which means it kills bacteria. This is in contrast to "bacteriostatic" antibiotics, which slow the growth and reproduction of bacteria but don't kill them directly.

Specifically, amoxicillin works by inhibiting bacterial cell wall synthesis by binding to what is known as penicillin-binding proteins (PBPs). These are located inside the bacterial cell wall.

Amoxicillin's ability to interfere with PBPs in the cell wall ultimately leads to cell lysis (i.e. the cell bursts).

How Fast Does Amoxicillin Work?

Amoxicillin will begin to work quickly after taking a dose. It's quickly absorbed, and peak concentrations in the blood occur around 1 to 2 hours after administration.

However, in general, it will take between 24-72 hours (1-3 days) to notice an improvement in symptoms. So, while amoxicillin goes to work quickly, it still takes time for our immune system to clear toxins and reduce inflammation.

What If You Don't Start To Feel Better?

Most studies, such as the guidelines to treat ear infections in children, recommend that if no clinical improvement is seen within 48-72 hours of starting amoxicillin, therapy should be reevaluated.

Similarly, the American Academy of Pediatrics guidelines for the treatment of sinusitis states the following:

"Amoxicillin with or without clavulanate is the firstline treatment of acute bacterial sinusitis. Clinicians should reassess initial management if there is either a caregiver report of worsening (progression of initial signs/symptoms or appearance of new signs/symptoms) or failure to improve within 72 hours of initial management."

So overall, amoxicillin is absorbed quickly after taking a dose by mouth, and you should feel improvement in your symptoms within 72 hours. If you do not, it is important to speak with your doctor as your infection may be resistant to the antibiotic, and alternative therapy options should be considered.

Alternative therapies include:

  • Augmentin (amoxicillin; clavulanic acid)
  • Doxycycline
  • Clindamycin
  • Levofloxacin (uncommonly used as the risks tend to outweigh the benefits)

Please let us know if we can be of any further help to you!


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Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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