Most uncomplicated urinary tract infections are treated with a short course of antibiotics, typically lasting 3 to 7 days depending on the drug. The three most commonly recommended first-line options are nitrofurantoin, trimethoprim-sulfamethoxazole (often sold as Bactrim or Septra), and fosfomycin. Which one you’re prescribed depends on local resistance patterns, your medical history, and whether the infection is straightforward or complicated.
First-Line Antibiotics for Simple UTIs
A simple, or uncomplicated, UTI is a bladder infection in an otherwise healthy person with a normal urinary tract. For these infections, three antibiotics are considered the best starting options:
- Nitrofurantoin: 100 mg twice daily for 7 days. It concentrates heavily in urine, which makes it effective against bladder infections specifically. It’s been in use for over 60 years and bacteria have been slow to develop resistance to it.
- Trimethoprim-sulfamethoxazole (TMP-SMX): One double-strength tablet twice daily for 3 days. This is the classic UTI antibiotic many people recognize by the brand names Bactrim or Septra. Treatment is shorter, but resistance is a growing concern in some areas.
- Fosfomycin: A single 3-gram dose taken just once. It’s the most convenient option since you only take one packet of medication, though it may be slightly less effective than a multi-day course of other antibiotics.
Your provider will often choose based on what bacteria in your region are still susceptible to. In some communities, resistance to TMP-SMX has climbed high enough that nitrofurantoin or fosfomycin becomes the safer bet.
Why Antibiotic Resistance Matters for UTIs
The bacterium behind most UTIs, E. coli, has become increasingly resistant to common antibiotics. A study tracking resistance trends at a San Francisco hospital network found that roughly 29% of E. coli samples were resistant to TMP-SMX, and about 24% were resistant to fluoroquinolones like ciprofloxacin. One particularly aggressive strain, called ST131, showed fluoroquinolone resistance as high as 77%.
This is why doctors sometimes order a urine culture before prescribing, especially if you’ve had UTIs before or a recent course of antibiotics. The culture identifies exactly which bacteria is causing your infection and which drugs will work against it. If you’re given an antibiotic and your symptoms aren’t improving within 2 to 3 days, resistance could be the reason.
When Stronger Antibiotics Are Needed
Fluoroquinolones like ciprofloxacin (250 mg twice daily for 3 days) were once widely prescribed for routine UTIs. They’re effective, but they carry a higher risk of serious side effects affecting tendons, nerves, and muscles. Current guidelines reserve them for situations where first-line drugs aren’t an option or the infection is more severe.
Complicated UTIs are a different category entirely. These include kidney infections (pyelonephritis), infections in people with urinary catheters, structural abnormalities of the urinary tract, or UTIs that have spread to the bloodstream. For complicated infections, treatment typically lasts 5 to 7 days and may involve broader-spectrum antibiotics. People who are severely ill or showing signs of sepsis often start on intravenous antibiotics in the hospital before switching to oral medication once they improve. The 2025 Infectious Diseases Society of America guidelines recommend shorter courses of 7 days for most complicated UTIs, rather than the older standard of 10 to 14 days.
Pain Relief While Antibiotics Work
Antibiotics start killing bacteria quickly, but you may still feel burning, urgency, and pelvic pressure for the first day or two. Phenazopyridine is an over-the-counter urinary pain reliever that numbs the lining of your urinary tract. The standard dose is 200 mg three times a day. It’s meant for short-term use only, generally no more than 2 days when taken alongside antibiotics.
One thing that catches people off guard: phenazopyridine turns your urine bright orange or red. This is harmless, but it can stain underwear and contact lenses. It doesn’t treat the infection itself. It simply takes the edge off while your antibiotic does its job.
UTI Treatment During Pregnancy
UTIs are common during pregnancy and are treated more aggressively because untreated infections can lead to kidney infections and complications. However, not all antibiotics are safe during pregnancy. The American College of Obstetricians and Gynecologists has flagged both nitrofurantoin and sulfonamide-containing drugs (like TMP-SMX) as potential concerns during the first trimester due to a possible link with certain birth defects. These drugs may still be prescribed when alternatives aren’t suitable, but cephalexin is often preferred as a safer first-trimester option. During the second and third trimesters, the range of safe choices broadens.
Nitrofurantoin and Kidney Function
If you have reduced kidney function, nitrofurantoin may not be appropriate for you. The drug is filtered through the kidneys and concentrated in urine, so when the kidneys aren’t working well, not enough of the drug reaches the bladder to be effective, and it can accumulate in the bloodstream and cause side effects. It’s contraindicated when kidney filtration rate falls below 45 mL/min. In borderline cases (filtration rate between 30 and 44), a short course of 3 to 7 days may still be considered for infections caused by multidrug-resistant bacteria where other options are limited.
Preventing Recurrent UTIs
Some people deal with UTIs repeatedly, defined as two or more infections in six months or three or more in a year. For prevention, low-dose antibiotics taken daily or after sex have traditionally been the standard approach, but this raises concerns about promoting antibiotic resistance over time.
A non-antibiotic alternative called methenamine hippurate works differently. It breaks down into formaldehyde in acidic urine, which sterilizes the bladder without the selective pressure that breeds resistant bacteria. A randomized trial in older women found that methenamine hippurate reduced recurrent UTIs by about 25% over a six-month treatment period. The side effects are mild compared to long-term antibiotic use. One important caveat: stopping the medication tends to lead to a rebound in UTI frequency, so it works best as an ongoing preventive measure rather than a short-term fix.