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