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Key takeaways
Kidney infections, known as pyelonephritis, happen when a lower urinary tract infection spreads upward from the bladder to the kidneys.
One possible course of treatment for kidney infections is the antibiotic amoxicillin.
Amoxicillin is typically prescribed for less severe kidney infections that are easily treated, but it can also be used at higher doses for pyelonephritis.
A urinary tract infection (UTI) is a common bacterial infection of the urethra or bladder, affecting nearly 50 to 60% of women in their lifetime. When a lower urinary tract infection spreads upward into the kidneys, it becomes a more severe condition known as an upper urinary tract infection or kidney infection (pyelonephritis). Once a healthcare provider has made a diagnosis of a kidney infection, one of the most common treatments is oral antibiotics, such as amoxicillin.
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Does amoxicillin treat a kidney infection?
Amoxicillin can treat a kidney infection, but it’s not always the first line of defense.
“[Amoxicillin] is usually chosen when the bacteria causing the infection are known to be sensitive,” explained Dr. Michael Genovese, a physician and Chief Medical adviser at Ascendant New York. “Doctors often rely on antibiotics like ciprofloxacin or trimethoprim-sulfamethoxazole, which can be more effective in certain cases.”
The success rate of amoxicillin for kidney infection depends on the type of bacteria that caused the underlying infection. Different types of bacteria can cause the initial UTI that leads to a kidney infection. There are uncomplicated UTIs and complicated UTIs, which are more difficult to treat. If the bacteria is a stronger strain or an antibiotic-resistant type, then the healthcare provider may recommend something stronger than amoxicillin.
When seeking treatment for a suspected kidney infection, your healthcare provider will review your medical history and symptoms. Common symptoms of pyelonephritis resemble UTI symptoms and include:
- Fever
- Chills
- Tenderness or pain in your lower back or sides (flank pain)
- Nausea or vomiting
- Frequent urination that can be painful
- Urine that is foul-smelling or cloudy
- Blood in the urine
If you experience these symptoms of a kidney infection, it’s vital to seek medical attention from a healthcare professional to develop a treatment plan. If the original bladder infection spreads into the kidneys and goes untreated, creating an even more severe infection, people can be at risk of additional complications, such as abscess formation or kidney failure.
After reviewing your symptoms, diagnostic testing will be ordered so the healthcare provider can best treat your infection. Urinalysis and urine culture are the most common tests to determine the presence of a UTI or pyelonephritis, and they require a urine sample. For more complicated cases, an antibiotic susceptibility analysis may be performed to determine which bacteria is causing the infection and which antibiotic they can be treated with. The most common bacteria causing acute pyelonephritis is Escherichia coli, commonly referred to as E. coli.
Risk factors for developing a UTI include having recent sexual intercourse, underlying conditions in the urinary tract, a history of recurrent UTIs, and poor hygiene, such as in children who have just become potty-trained. Pregnant women, older adult patients, and those with a lowered immune system are also at higher risk.
For most people, a standard treatment option for a kidney infection is a course of antibiotics. This antibiotic treatment typically lasts between three and 14 days.
Amoxicillin dosage for a kidney infection
“Typically, the amoxicillin dosage for a kidney infection is 500 mg to 875 mg every eight to 12 hours for adults,” said Dr. Genovese. He added, “However, the exact dose and duration should be tailored by a healthcare provider based on factors like the infection’s severity and other health considerations.”
This is higher than the typical dosage of amoxicillin given for UTIs, which ranges from 250 to 500 mg every eight hours.
There are several other commonly used antibiotics given for kidney infections. Amoxicillin and amoxicillin-clavulanate are part of the Penicillin group of antibiotics, but different groups of antibiotics, including cephalosporins, fluoroquinolones, aminoglycosides, and others, may be prescribed. Some of the most popular treatments for pyelonephritis include Bactrim, ciprofloxacin, and Septra.
How long after taking amoxicillin do symptoms of a kidney infection typically subside?
“Most patients who are symptomatic can find relief within 24 to 48 hours of starting antibiotics,” said Dr. Sean Devlin, the Chief Medical Officer of Brio-Medical in Scottsdale, Arizona.
At home, be sure to drink plenty of fluids, which can help speed up recovery.
While amoxicillin begins reducing kidney infection symptoms within a day or two, it doesn’t mean you’re finished taking your medicine. It’s always important to finish a course of antibiotics, even if you feel fine, as the underlying bacteria can obtain antibiotic resistance, leading to further complications. According to Dr. Devlin, “Antibiotic courses can run from three to 14 days, depending on the specific antibiotic, as well as characteristics of the patient and infection.”
Sometimes, the symptoms of a kidney infection or UTI persist after a course of antibiotics. A study in 2021, which examined over 670,000 women, found that UTIs that aren’t cured with their first round of treatment are typically caused by inappropriate antibiotic agents or incorrect durations of treatment. If your symptoms linger after finishing antibiotics, it’s important to contact your healthcare provider for further medical treatment.
Disorders that are not UTIs but have similar symptoms also require different treatment. These can include interstitial cystitis and kidney stones.
Side effects of amoxicillin for a kidney infection
As with any medication, there are possible side effects associated with amoxicillin. One potential side effect of any antibiotic treatment is yeast infections and antibiotic-associated diarrhea, as antibiotics can also disturb the balance of healthy bacteria in your body.
Dr. Genovese explained, “Amoxicillin is generally well-tolerated, but it can have some mild side effects.” According to him, typical side effects of amoxicillin can include:
- Nausea
- Diarrhea
- Stomach upset
- Skin rash
A skin rash can indicate an allergic reaction and should be monitored. Some patients may indeed experience an allergic reaction to amoxicillin, characterized by itching, hives, throat swelling, or difficulty breathing (anaphylaxis). If this occurs, seek immediate medical attention.
“If you ever have concerns about side effects or feel your symptoms are not improving, do not hesitate to contact your healthcare provider for support,” advised Dr. Genovese.
When is amoxicillin NOT the preferred treatment?
Although amoxicillin or amoxicillin-clavulanate are both appropriate options to treat urinary tract infections, they are often not the first choice for many providers. Nitrofurantoin (Macrobid) is the typical preferred first-line agent for acute, uncomplicated lower urinary tract infections (urethra and bladder). It is usually given twice daily for five to seven days. It is very effective and has low antibiotic resistance in most areas.
After Macrobid, trimethoprim-sulfamethoxazole (Bactrim) is the usual second-line treatment for uncomplicated UTIs. This medication is given twice daily for 14 days in most cases. Bactrim is not commonly used as a first-line antibiotic because it is slightly less effective than Macrobid and has a longer treatment duration.
The fluoroquinolones ciprofloxacin (Cipro) and levofloxacin (Levaquin) are commonly prescribed first-line agents for complicated UTIs or infections that have reached the kidneys. The reason for this choice is twofold: they effectively treat the bacteria that cause UTIs (low resistance), and they consistently reach the urinary tract and kidneys (high tissue penetration).
Ciprofloxacin is typically taken twice daily for seven days, while levofloxacin is generally taken once daily for five days.
The beta-lactams, of which amoxicillin is one type, are usually the third-line treatment for urinary tract infections or pyelonephritis. The other choices in this group of antibiotics include cefdinir, cefpodoxime, and cephalexin. They are typically prescribed two to four times daily for 10-14 days. The reason amoxicillin and the other beta-lactams are not usually first-line agents is that they are slightly less effective, have a somewhat higher relapse rate, and a longer treatment duration compared to the fluoroquinolones.
Best antibiotic for a kidney infection
With all of these choices of antibiotics for UTIs, how do we know which one is the best? The answer may be multifactorial and ultimately dependent on your individual healthcare provider. Your healthcare provider may prefer certain antibiotics due to familiarity with the medication, better insurance coverage, or lower bacterial resistance in that particular area of the country. It will also depend on what has worked for you in the past, the allergies you have, and any other medications you are taking. Ultimately, the choice of antibiotic used for a UTI or kidney infection will require a discussion between you and your provider.
Monitoring treatment and when to seek further medical attention
If your antibiotic is working as it should, you should start feeling better within two to three days. If you are still experiencing symptoms after five to seven days of treatment (such as pain on urination, cloudy urine, fever, or flank pain), contact your prescribing provider and inform them.
- An introduction to the epidemiology and burden of urinary tract infections, Therapeutic Advances in Urology (2019)
- International clinical practice guidelines for the treatment of acute uncomplicated cystitis and pyelonephritis in women, Clinical Infectious Diseases (2011)
- Diagnosis and management of acute pyelonephritis in adults, American Family Physician (2005)
- Rural-urban differences in antibiotic prescribing for uncomplicated urinary tract infection, Cambridge University Press (2021)
- Acute complicated urinary tract infections (including pyelonephritis) in adults, UpToDate (2025)