The most commonly prescribed antibiotics for a kidney infection are fluoroquinolones like ciprofloxacin and levofloxacin, or a cephalosporin called ceftriaxone. Which one you receive depends on whether you can be treated at home with pills or need IV antibiotics in a hospital, along with local patterns of bacterial resistance in your area.
Kidney infections (the medical term is pyelonephritis) are more serious than ordinary bladder infections. The bacteria have traveled up into the kidney tissue itself, which means the antibiotic needs to reach high enough concentrations in both the blood and kidney to clear the infection. That rules out some common UTI drugs and narrows the options.
Oral Antibiotics for Outpatient Treatment
Most uncomplicated kidney infections in otherwise healthy adults can be treated at home with oral antibiotics. The standard options are ciprofloxacin, taken twice daily for 7 days, or levofloxacin, taken once daily for 5 days. These fluoroquinolones are the go-to choice in areas where fewer than 10% of E. coli strains (the bacteria behind most kidney infections) are resistant to them.
Trimethoprim-sulfamethoxazole (commonly known as Bactrim) is another effective oral option, but only if lab testing confirms the specific bacteria causing your infection is susceptible to it. Because resistance rates are higher with this drug, doctors typically won’t prescribe it until urine culture results come back. When the bacteria is sensitive, though, UCSF guidelines actually list it as a preferred oral choice.
If your doctor is concerned about fluoroquinolone resistance in your region (rates above 10%), you may get a single injection of ceftriaxone in the office or emergency room before starting your oral course. This one-time shot gives you a head start against the infection while your pills take effect.
IV Antibiotics for Hospital Treatment
Some kidney infections require hospitalization and intravenous antibiotics. This is typically the case when you can’t keep fluids or pills down, you have a high fever that isn’t responding, or your infection is considered complicated due to an underlying condition like a kidney stone or structural abnormality.
In the hospital, the most common IV options include ceftriaxone (given once daily), ciprofloxacin or levofloxacin (if local resistance rates allow), and ertapenem. Your medical team will collect a urine culture and adjust the antibiotic once they know exactly which bacteria is involved and what it responds to. Once your fever has been gone for about 48 hours and you’re able to eat and drink normally, treatment is usually switched to an oral antibiotic to finish the course at home.
Antibiotics That Don’t Work for Kidney Infections
Two drugs frequently prescribed for bladder infections are not effective for kidney infections, and this is a point worth understanding if you’ve been treated for UTIs before. Nitrofurantoin (Macrobid) and fosfomycin both concentrate well in the bladder but do not reach therapeutic levels in kidney tissue or the bloodstream. Using either of these for a kidney infection risks undertreating a serious condition.
Treatment During Pregnancy
Kidney infections in pregnancy are treated more aggressively. The standard approach is hospital admission with IV ceftriaxone until the fever has been gone for 48 hours, followed by a switch to an oral antibiotic based on culture results. Fluoroquinolones are not used during pregnancy, and certain other antibiotics carry risks for the developing baby. For example, aminoglycosides (a class of IV antibiotics) have been linked to hearing damage in the fetus with prolonged exposure and are reserved for situations where safer options aren’t tolerated.
Treatment in Children
Children with kidney infections, particularly infants and toddlers with a fever, are treated with either oral or IV antibiotics depending on how sick they are. A child who can’t keep fluids down or appears very ill typically receives IV ceftriaxone or a similar cephalosporin until improvement begins, usually within 24 to 48 hours, before switching to an oral antibiotic.
For oral treatment, common choices include cephalosporins (such as cefixime or cephalexin), amoxicillin-clavulanate, or trimethoprim-sulfamethoxazole. Doses are calculated by the child’s weight. Treatment typically lasts 7 to 14 days. As with adults, nitrofurantoin should not be used for kidney infections in children because it doesn’t reach adequate levels in the kidneys or blood.
How Long Treatment Lasts
For uncomplicated cases in adults, antibiotic courses range from 5 to 14 days depending on the drug. Levofloxacin requires only 5 days, ciprofloxacin is prescribed for 7 days, and trimethoprim-sulfamethoxazole courses often run 10 to 14 days. Symptoms generally begin to improve within a few days of starting treatment, though it’s important to complete the full course even after you feel better.
If your symptoms haven’t improved after 48 to 72 hours on antibiotics, that’s a signal something may need to change. The bacteria may be resistant to the drug you’re taking, or there could be a complication like a kidney abscess or an obstructing stone that antibiotics alone can’t resolve. Your doctor will typically recheck culture results and may order imaging at that point.
Why Urine Cultures Matter
Nearly every kidney infection should have a urine culture collected before or at the start of treatment. Initial antibiotic choices are “empiric,” meaning they’re educated guesses based on the most likely bacteria and local resistance patterns. Once the culture identifies the exact organism and which drugs kill it, your doctor can narrow or change the antibiotic to the most effective, least broad option. This is why you may be started on one antibiotic and switched to another a few days later. It’s not a sign that something went wrong. It’s how the process is designed to work.