How Long Does Amoxicillin Last In Your Body?

Amoxicillin 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 amoxicillin by mouth, it 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. the time it takes the 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. In most individuals, an entire dose of amoxicillin would be eliminated within a day.

How Kidney Function Plays A Role

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 the 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 still room for individual variability.

Final Words

It is important to reach out to your doctor to discuss your concerns if you are still seeing symptoms of infection, or if you feel like the 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.