Pyelonephritis is a bacterial infection of the kidneys that requires prompt medical attention and treatment with antibiotics to prevent serious complications and permanent kidney damage.

Understanding Treatment Goals for Kidney Infections

When someone develops pyelonephritis, the main goal of treatment is to eliminate the bacterial infection as quickly as possible to prevent it from causing lasting harm to the kidneys. Unlike simple bladder infections, kidney infections can lead to serious health problems if not treated promptly and properly. The treatment approach focuses on stopping the infection, relieving uncomfortable symptoms like fever and pain, and protecting the kidneys from permanent scarring or damage that could affect their function in the future.^[1]

Treatment decisions depend on several important factors, including how severe the infection is, whether the patient has other health conditions like diabetes or pregnancy, and whether there are any complications such as kidney stones or blockages in the urinary tract. Doctors also consider the patient’s age and overall health status when deciding whether treatment can happen at home with oral medications or requires hospitalization with intravenous antibiotics. Young, otherwise healthy women with uncomplicated kidney infections can often be treated as outpatients, while pregnant women, elderly patients, those with weakened immune systems, and people with severe symptoms typically need hospital care.^[2][11]

Medical societies and expert organizations have developed standard treatment guidelines based on years of research and clinical experience. These guidelines help doctors choose the most effective antibiotics and determine how long treatment should continue. At the same time, researchers are continually studying new treatment approaches and testing different antibiotics in clinical trials to find better ways to manage kidney infections, especially as bacteria become resistant to commonly used medications. This ongoing research is essential because the bacteria that cause pyelonephritis are evolving and becoming harder to treat with traditional antibiotics.^[15]

Standard Treatment Approaches

The cornerstone of treating pyelonephritis is antibiotic therapy, which means using medications that kill or stop the growth of bacteria. The choice of which antibiotic to use initially depends on the most common bacteria in the community and how resistant they are to different medications. In most cases, the infection is caused by a type of bacteria called Escherichia coli (E. coli), which normally lives in the intestines but can travel up the urinary tract and infect the kidneys. Other bacteria such as Proteus mirabilis, Enterobacter, and Staphylococcus can also cause kidney infections.^[1][10]

For patients who can be treated at home, doctors often prescribe a group of antibiotics called fluoroquinolones. The most commonly used fluoroquinolones are ciprofloxacin and levofloxacin. Ciprofloxacin is typically given at a dose of 500 milligrams by mouth twice daily for seven days, or as an extended-release version of 1,000 milligrams once daily for seven days. Levofloxacin is usually prescribed at 750 milligrams once daily for five days. These medications work by interfering with the bacteria’s ability to copy their genetic material, which stops them from multiplying and eventually kills them.^[11][13]

When fluoroquinolone resistance rates are high in a community, or when a patient cannot take fluoroquinolones, doctors may give an initial injection of ceftriaxone, which is a type of antibiotic called a cephalosporin. Ceftriaxone is given as a single dose of 1 gram either into a muscle or into a vein, followed by oral fluoroquinolone treatment. Another option is gentamicin, which belongs to a class of antibiotics called aminoglycosides. Gentamicin is given as a single dose calculated based on the patient’s weight (7 milligrams per kilogram) and is followed by oral antibiotics. For patients with severe allergies to penicillin-type antibiotics who might also have resistant bacteria, ertapenem (a type of carbapenem antibiotic) can be given as a 1-gram injection.^[13]

Although an antibiotic called trimethoprim-sulfamethoxazole was commonly used in the past to treat urinary tract infections, it is no longer recommended as a first choice for treating kidney infections because many bacteria have developed resistance to it. However, if laboratory testing shows that the specific bacteria causing a patient’s infection is still sensitive to this medication, it can be used at a dose of 160/800 milligrams (one double-strength tablet) twice daily for 14 days. Similarly, oral antibiotics in the beta-lactam family (which includes penicillins and cephalosporins) are generally not preferred for outpatient treatment because they have historically been associated with higher rates of treatment failure and infection recurrence, even when the bacteria appear sensitive to them in laboratory tests.^[11][13]

For patients who need to be hospitalized because their infection is severe, they have concerning symptoms like persistent vomiting that prevents them from keeping down oral medications, they show signs of sepsis (a life-threatening response to infection affecting the whole body), or they have complicated medical conditions, intravenous antibiotics are administered. Several antibiotic options are available for hospitalized patients. Fluoroquinolones like ciprofloxacin (400 milligrams every 12 hours) or levofloxacin (500 milligrams once daily) can be given through an intravenous line. Aminoglycosides, either alone or combined with ampicillin, are another option. Extended-spectrum cephalosporins such as ceftriaxone or cefepime, sometimes combined with an aminoglycoside, can also be used. For very resistant bacteria or severe infections, carbapenem antibiotics like ertapenem, meropenem, or imipenem may be necessary.^[12][15]

The duration of antibiotic treatment typically ranges from 7 to 14 days, depending on which medication is used and how quickly the patient responds. Levofloxacin can be given for a shorter course of 5 days, while most other antibiotics require 7 to 10 days or longer. It is absolutely essential that patients complete the entire prescribed course of antibiotics, even if they start feeling better after just a few days. Stopping antibiotics too early can allow the infection to return, often in a form that is more difficult to treat because the remaining bacteria may have developed resistance to the medication.^[14][19]

Before starting antibiotics, doctors always collect a urine sample for laboratory testing. This sample undergoes two important tests: a urinalysis, which looks for signs of infection like white blood cells, bacteria, and blood in the urine, and a urine culture, which identifies the specific type of bacteria causing the infection and determines which antibiotics it is sensitive or resistant to. These culture results usually take 24 to 48 hours to become available. If the patient is not improving as expected with the initial antibiotic choice, the doctor uses the culture results to switch to a more effective medication. Blood cultures may also be obtained, especially in hospitalized patients, because bacteria from a kidney infection can sometimes enter the bloodstream.^[14][19]

In addition to antibiotics, supportive treatments help manage symptoms and aid recovery. Patients are encouraged to drink plenty of fluids, typically 8 to 12 glasses of water or other clear liquids each day, unless they have medical conditions like heart disease, kidney disease, or liver disease that require limiting fluid intake. Drinking fluids helps flush bacteria out of the urinary system and prevents dehydration, especially when fever is present. Pain relief medications such as acetaminophen or ibuprofen can reduce fever and relieve the pain in the lower back or side that is characteristic of kidney infections. For burning or discomfort during urination, some doctors may prescribe phenazopyridine, a medication that numbs the urinary tract lining.^[17][18]

Most patients with uncomplicated pyelonephritis begin to feel better within 2 to 3 days of starting antibiotics. However, close follow-up is critical, especially for outpatients. Doctors typically schedule a follow-up visit or phone call within 1 to 2 days of starting treatment to make sure symptoms are improving. If symptoms persist or worsen despite antibiotic treatment, additional testing or hospitalization may be needed. Some patients may require a repeat urine culture after completing antibiotics to confirm the infection has been completely eliminated.^[12]

Possible Side Effects of Standard Treatment

Like all medications, antibiotics used to treat pyelonephritis can cause side effects. Fluoroquinolones, while effective, have been associated with several concerning side effects that led the U.S. Food and Drug Administration to issue special warnings. These antibiotics can cause tendon inflammation or rupture, especially of the Achilles tendon in the heel. They may also affect the nervous system, causing symptoms like anxiety, confusion, hallucinations, depression, or peripheral neuropathy (nerve damage in the hands and feet). In some people, fluoroquinolones can worsen a condition called myasthenia gravis, which causes muscle weakness. Because of these risks, fluoroquinolones should be reserved for situations where other antibiotics are not suitable.^[11]

Gastrointestinal side effects are common with many antibiotics. Nausea, vomiting, diarrhea, and abdominal cramping can occur with fluoroquinolones, cephalosporins, and other antibiotic classes. These symptoms are usually mild and resolve once treatment is completed. However, antibiotics can also disrupt the normal balance of bacteria in the intestines, sometimes leading to an infection with a bacterium called Clostridioides difficile, which causes severe diarrhea and colitis. Aminoglycosides like gentamicin can affect kidney function and hearing, especially with prolonged use or in patients with existing kidney problems, though single-dose treatment carries minimal risk.^[12]

Allergic reactions to antibiotics can range from mild skin rashes to severe, life-threatening reactions called anaphylaxis. Patients who have had allergic reactions to penicillin or cephalosporins in the past should inform their doctor, as they may also react to related antibiotics. Trimethoprim-sulfamethoxazole commonly causes rash and sun sensitivity, and in rare cases can lead to serious skin reactions like Stevens-Johnson syndrome. Any patient who develops a rash, difficulty breathing, facial swelling, or severe skin peeling while taking antibiotics should seek immediate medical attention.^[11]

Treatment Approaches in Clinical Trials

As bacterial resistance to commonly used antibiotics continues to increase, researchers and pharmaceutical companies are actively testing new antibiotics and treatment strategies in clinical trials for complicated urinary tract infections, including pyelonephritis. These studies are essential because the bacteria that cause kidney infections are becoming increasingly resistant to fluoroquinolones, cephalosporins, and other traditional antibiotics. Some strains of E. coli now produce enzymes called extended-spectrum beta-lactamases (ESBLs) that break down many types of antibiotics, making infections much harder to treat.^[7][15]

Clinical trials for pyelonephritis typically progress through several phases. Phase I trials involve a small number of healthy volunteers or patients and primarily focus on determining whether a new drug is safe and what side effects it might cause. These studies also establish appropriate dosing ranges. Phase II trials involve more patients who actually have the disease being studied. These trials assess whether the new treatment is effective at eliminating the infection and continue to monitor for side effects. Phase III trials are large studies that compare the new treatment directly against currently used standard treatments to determine whether the new approach is at least as good as, or better than, existing options. These are the studies that typically lead to regulatory approval by agencies like the U.S. Food and Drug Administration or the European Medicines Agency.^[2]

Several newer antibiotics have been studied in recent years for treating complicated urinary tract infections and pyelonephritis. These include new formulations that combine existing antibiotics with beta-lactamase inhibitors, which are compounds that block the enzymes bacteria produce to resist antibiotics. One example is ceftolozane-tazobactam, which combines a cephalosporin antibiotic with a beta-lactamase inhibitor. Another is ceftazidime-avibactam, which uses a different but similar approach. These combination therapies can overcome resistance mechanisms that make bacteria immune to older antibiotics.^[15]

New carbapenem antibiotics and carbapenem combinations are also being tested. While carbapenems like ertapenem, meropenem, and imipenem are already used for resistant infections, some bacteria have even developed resistance to these powerful antibiotics. Newer agents like imipenem-relebactam and meropenem-vaborbactam combine a carbapenem with a novel beta-lactamase inhibitor to restore effectiveness against highly resistant bacteria. These medications have shown promise in clinical trials for complicated urinary tract infections and are particularly important for patients infected with carbapenem-resistant bacteria.^[15]

Researchers are also studying optimal treatment durations and whether shorter courses of antibiotics might be just as effective as longer courses, with the advantage of fewer side effects and less impact on the body’s normal bacterial populations. Some trials have investigated whether 5 to 7 days of treatment might be sufficient for certain patients who respond quickly to therapy, compared to the traditional 10 to 14 days. Understanding the minimum effective treatment duration is important for reducing antibiotic use and potentially slowing the development of resistance.^[15]

Clinical trials for pyelonephritis are conducted at medical centers and hospitals around the world, including sites in the United States, Europe, and other regions. Patients who participate in these trials receive close medical monitoring and follow-up. To be eligible for most clinical trials testing new antibiotics for pyelonephritis, patients generally must have a confirmed kidney infection diagnosed by symptoms, physical examination findings, and laboratory evidence of infection in the urine. However, certain patients may be excluded from trials, such as those who are pregnant, have severe kidney disease, have certain other serious medical conditions, or whose infections are caused by bacteria known to be resistant to the study medication.^[2]

Beyond new antibiotics, researchers are exploring other innovative approaches to treating and preventing kidney infections. Some studies are investigating the use of vaccines or immunotherapy approaches that could help the body’s immune system better fight off urinary tract infections before they spread to the kidneys. Other research focuses on identifying biomarkers—measurable substances in the blood or urine that could help predict which patients are at highest risk for complications or treatment failure, allowing doctors to tailor treatment more precisely to individual patients.^[2]

Most common treatment methods

• Fluoroquinolone antibiotics
  • Ciprofloxacin given as 500 mg orally twice daily for 7 days or 1,000 mg extended-release once daily for 7 days
  • Levofloxacin given as 750 mg orally once daily for 5 days
  • Appropriate for outpatient treatment when local resistance rates are 10% or less
  • Can also be given intravenously for hospitalized patients
• Cephalosporin antibiotics
  • Ceftriaxone given as a single 1-gram injection into muscle or vein
  • Often used as initial treatment before switching to oral antibiotics
  • Extended-spectrum cephalosporins like cefepime used for hospitalized patients
  • Effective against most common bacteria causing kidney infections
• Aminoglycoside antibiotics
  • Gentamicin given as single dose based on body weight (7 mg/kg)
  • Used as initial injection before oral antibiotic therapy
  • Also combined with other antibiotics for severe infections in hospitalized patients
  • Requires monitoring of kidney function with prolonged use
• Carbapenem antibiotics
  • Ertapenem, meropenem, or imipenem used for resistant or severe infections
  • Reserved for complicated cases or when bacteria are resistant to other antibiotics
  • Particularly important for infections with ESBL-producing bacteria
  • Typically given intravenously in hospital settings
• Trimethoprim-sulfamethoxazole
  • Given as 160/800 mg (double-strength tablet) twice daily for 14 days
  • Only used when bacteria are proven sensitive to this medication
  • Not recommended as first-line treatment due to high resistance rates
  • Still useful for some cases based on culture results
• Supportive care measures
  • Drinking 8 to 12 glasses of fluids daily to flush the urinary system
  • Pain relief medications like acetaminophen or ibuprofen for fever and discomfort
  • Urinary analgesics like phenazopyridine to reduce burning during urination
  • Rest and adequate nutrition to support the immune system during recovery

When Surgery May Be Necessary

While most cases of pyelonephritis respond well to antibiotic treatment, some situations require surgical intervention. If a patient continues to have fever or shows bacteria in their bloodstream for more than 48 hours despite appropriate antibiotics, doctors will investigate whether there is an underlying problem that needs to be corrected surgically. One such problem is a kidney or perinephric abscess, which is a collection of pus that forms in or around the kidney. Abscesses cannot be adequately treated with antibiotics alone and must be drained, either with a needle inserted through the skin under imaging guidance or through surgical incision.^[12]

Another serious complication that may require surgery is emphysematous pyelonephritis, a rare but life-threatening condition most often seen in people with diabetes. In this condition, gas-forming bacteria literally destroy kidney tissue and create pockets of gas within the kidney. This is a surgical emergency that usually requires removal of the damaged kidney tissue or, in severe cases, the entire kidney. Kidney stones that are blocking the urinary tract and causing infection also typically require removal, as antibiotics cannot adequately treat an infection when urine and bacteria are trapped behind an obstruction.^[1][10]

After recovering from a kidney infection, some patients may be candidates for elective surgery to correct anatomical problems that predispose them to recurrent infections. These might include repair of vesicoureteral reflux (a condition where urine flows backward from the bladder toward the kidneys), correction of congenital abnormalities of the urinary tract, removal of kidney stones, or treatment of an enlarged prostate in men. Addressing these underlying issues can help prevent future kidney infections and protect long-term kidney function.^[12]

Special Considerations for Different Patient Groups

Pregnant women with pyelonephritis require special attention because kidney infections during pregnancy increase the risk of premature delivery and other complications for both mother and baby. Pregnant women with kidney infections are almost always hospitalized for intravenous antibiotic treatment, even if they might otherwise be candidates for outpatient therapy. The choice of antibiotics is limited to those known to be safe during pregnancy. Fluoroquinolones are generally avoided in pregnant women because they may affect fetal bone and cartilage development. Instead, cephalosporins like ceftriaxone are preferred. Pregnant women also need more frequent monitoring and follow-up to ensure the infection is completely resolved.^[4][12]

Children with pyelonephritis also require special consideration. In young children, especially those under 2 years old, kidney infections can cause long-term kidney damage and scarring that may lead to high blood pressure and reduced kidney function later in life. Therefore, prompt treatment is essential. Children’s symptoms may be different from adults—newborns might refuse to feed or vomit without having a fever, while toddlers might have fever but may not be able to communicate where they hurt. Any child with fever and urinary symptoms should be evaluated promptly for possible kidney infection. Many cases in children are associated with vesicoureteral reflux, and children who have had kidney infections may need additional testing to look for this and other anatomical abnormalities.^[6]

Elderly patients and those with weakened immune systems face higher risks from kidney infections. People over 65, those with diabetes, cancer patients receiving chemotherapy, organ transplant recipients taking immunosuppressive medications, and people with HIV or other conditions affecting the immune system are more likely to develop severe infections and complications. These patients generally require hospitalization for treatment, even with moderate symptoms, and may need longer courses of antibiotics. They are also at higher risk for developing antibiotic-resistant infections and may need more aggressive antibiotic regimens.^[2][7]