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 Jul 19, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jul 19, 2018

Amoxicillin 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 as 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 dosing as 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. While amoxicillin goes to work quickly, it still takes time for our bodies and immune system to clear toxins, reduce inflammation etc...

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 treatment of sinusitis state 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."

Lastly, while the Infectious Disease Society of America doesn't recommend amoxicillin for most UTIs due to bacterial resistance (Augmentin, which is a combination of amoxicillin;clavulanic acid, is a more preferred choice), symptom improvement is often seen within 24-48 hours.

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.

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Office: 716-389-3076

About Amoxicillin

Amoxicillin is an semisynthetic "aminopenicillin" similar to ampicillin and penicillin. It does however, have a broader spectrum of antibacterial effects than penicillin and is better absorbed than ampicillin. Amoxicillin is used to treat a variety of infections including: Otitis media, bronchitis, sinusitis, and bacterial cystitis. In general, amoxicillin can be given with or without food but food may reduce any gastrointestinal side effects.

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