How long does it take for antibiotics to work? It depends, but a full course is required.

How one needs to take antibiotics can be a little bit confusing because oftentimes you feel better after a few days, but still have several days worth of antibiotics doses to take. Why is that? 

It’s vital to follow the instructions your provider gives you on how to take your antibiotics. Taking the full course of antibiotics ensures you have wiped out the existing infection, and this can combat antibiotic resistance. 

We spoke with Dr. Neha Narula, a family medicine physician with Stanford Healthcare, to help explain how long it takes antibiotics to “work” in all aspects of the word – how long it takes to feel better and how long it takes to clear the infection and prevent antibiotic resistance. 

How long does it take for antibiotics to kick in?

It depends on a few different factors, like the type and severity of the infection, the type of antibiotic used and the health factors of the individual. It can also be affected by antibiotic resistance rates in the community. 

For some types of infections, symptoms can start to improve very quickly after the initiation of antibiotics. Narula says, “In some cases, for example, in urinary tract infections, symptoms can start to improve within a day or two after starting appropriate antibiotic treatment. Whereas in other cases, (like respiratory infections) it can take several days or even up to a week before significant improvement is seen.”

How quickly do antibiotics clear up an infection?

How fast an infection clears out is also dependent on a few variables. Narula explains, “For an infection to clear out, there are several variable factors: the location and severity of infection, the effectiveness of the prescribed antibiotic and personal patient factors like their medical history, other medications they are on, and how well their kidneys and liver function. Common infections like skin or urinary tract infections may take 7 to 14 days to clear. However, severe and complicated infections, like bone infections or even certain pneumonia cases, can take several weeks to even months.” 

Narula emphasizes the need to complete the course of antibiotics. “It is important to note that even if symptomatically things may seem like they are improving, it is so crucial to complete the course of antibiotics to eradicate all of the bacteria that was causing the infection and ultimately prevent resistance of bacteria and recurrent or persistent infections,” she urges. 

Dr. Jessica Ruth Lee, an internal medicine physician at the University of Maryland Medical Center and an assistant professor at the University of Maryland School of Medicine, echoes the importance of taking antibiotics appropriately, “Taking antibiotics is not without its own risks. When you call your doctor asking for antibiotics for a sinus infection, for example, I am sure your doctor asks you to come in to clinic to be evaluated.

"This is because taking antibiotics frequently can lead to antibiotic resistance. This means the bacteria that cause an infection learn to outsmart the antibiotics, therefore making antibiotics ineffective. We are not trying to inconvenience you when we ask you to come in. We want to make sure you truly have a sinus infection that warrants antibiotics so we can limit your exposure to unnecessary medications.”

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