How Long Does Amoxicillin Last In Your Body?

In our latest question and answer, the pharmacist discusses how long the antibiotic amoxicillin stays in your system (i.e. body).

How Long Does Amoxicillin Last In Your Body?
Apr 05, 2018

Newmommylife asked

Hello my 7 month old was prescribed amoxicillin for an ear infection. It has been about one week and a half since he completed the medication, but every now and the I still smell the antibiotics in his urine. How long does it take for the medication to clear the body?

Answer

How Long Amoxicillin Lasts In The SystemAmoxicillin is a broad-spectrum antibiotic that is used for a wide range of bacterial infections in nearly every age group (e.g. infants to the elderly). It is most commonly used for the following infections:

  • Middle ear infections
  • Pneumonia
  • Upper respiratory tract infections
  • Urinary tract infections
  • Sinusitis

How long amoxicillin lasts in your system mostly depends on the age of the individual taking the medication and kidney function, as discussed below.

How Long Amoxicillin Stays In Your System

After taking by mouth, amoxicillin is rapidly absorbed. Peak concentrations in the blood occur around 1 to 2 hours after dosing for immediate release formulations of amoxicillin (e.g capsules, suspensions, tablets). 

The half-life of amoxicillin (i.e. time it takes to body to metabolize 50% of the drug) is relatively short, around 1 to 1.5 hours (60 to 90 minutes). Studies have shown that more than 60% of a dose of amoxicillin is eliminated in the urine within 6 to 8 hours.

Since amoxicillin is eliminated mostly via the kidneys, kidney function plays a huge role in how long amoxicillin lasts in the body.

Based on the known half-life of amoxicillin, individuals with normal kidney function should eliminate most, if not all of an amoxicillin dose within 24 hours. However, the elimination half-life of amoxicillin is greatly increased as kidney function decreases.

Studies in adults have shown that the elimination half-life can increase to over 12 hours in those with kidney disease or severe impairment. This would significantly increase the time it takes for a total dose of amoxicillin to be eliminated in the body, most likely by a few days.

Similarly, newborns and infants do not have completely developed kidney function and elimination of amoxicillin from the body is greatly delayed when compared to children and adults. The reported half-life of amoxicillin in newborns has varied considerably by study:

  • One drug monograph lists the half-life at 3.7 in newborns.
  • One study lists a half-life of between 1.79 and 8.9 hours in newborns.
  • Another study lists an average half-life of 5.2 hours in preterm newborns.

What we can tell from the information above is that the half-life of amoxicillin in newborns is variable, so how long amoxicillin stays in the system is variable as well.

Taking the higher end of the half-life range (e.g. 8.9 hours), we would expect a dose of amoxicillin to be completely cleared from the body within 2 to 4 days. Nevertheless, there is a still room for individual variability.

Conclusion

It is important to reach out to your doctor to discuss your concerns if you are still seeing symptoms of infection, or you feel like medication prescribed is causing adverse reactions (such as prolonged foul smelling urine). It could be indicative of a recurrent infection or a problem with how the drug is being metabolized. 

Summary

  • Amoxicillin has a relatively short half-life of around 1 to 1.5 hours (60 to 90 minutes) in healthy adults.
  • For healthy adults, amoxicillin should be cleared from your system within 24 hours.
  • In those with decreased kidney function, complete elimination of amoxicillin could take 2 to 4 days.
  • Similarly, in newborns, amoxicillin can take 2 to 4 days, if not longer, to completely clear amoxicillin in the system to due kidney function not being fully developed.

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