The most commonly recommended antibiotics for an uncomplicated UTI are nitrofurantoin and trimethoprim-sulfamethoxazole (often called Bactrim or Septra). Both clear the infection in about 90% of cases within days. Which one your provider prescribes depends on local resistance patterns, your medical history, and whether you’re pregnant.
First-Line Options for Uncomplicated UTIs
For a straightforward bladder infection in an otherwise healthy person, treatment guidelines consistently point to two top choices. Nitrofurantoin is taken twice daily for five days. Trimethoprim-sulfamethoxazole is taken twice daily for three days. In clinical trials comparing the two head-to-head, both achieved about 90% clinical cure within a week of finishing treatment, and bacterial clearance rates were 91-92%.
A third option, fosfomycin, stands out because it’s a single dose: one packet of powder mixed with water, taken once. A meta-analysis of multiple trials found that single-dose fosfomycin produced clinical and microbiological results comparable to multi-day courses of other antibiotics. The convenience is obvious, but some data suggest its long-term cure rates may be slightly lower than a full course of nitrofurantoin or trimethoprim-sulfamethoxazole.
Side effects for all three are generally mild and mostly gastrointestinal. In a randomized trial comparing nitrofurantoin and fosfomycin, nausea occurred in about 2-3% of patients in both groups, and diarrhea in about 1%.
Why Your Provider Might Skip Trimethoprim-Sulfamethoxazole
Trimethoprim-sulfamethoxazole works well when the bacteria causing your infection are susceptible to it. The problem is that resistance has been climbing. Guidelines recommend it only when local resistance rates stay below 20%. Recent surveillance data from the Infectious Diseases Society of America show that resistance among common urinary bacteria collected from outpatients across all U.S. regions now exceeds the thresholds set in the 2010 guidelines. That means in many communities, your provider may default to nitrofurantoin or fosfomycin instead, since resistance to those drugs remains low.
If you’ve had a urine culture done and the lab confirms your specific bacteria is susceptible, trimethoprim-sulfamethoxazole is still a perfectly effective three-day option. Without that culture result, though, your provider is making an educated guess, and nitrofurantoin is often the safer bet.
Why Ciprofloxacin Is No Longer a Go-To
Ciprofloxacin and other fluoroquinolones were once widely prescribed for UTIs. That’s changed. The FDA now requires labeling that reserves fluoroquinolones for situations where no alternative treatment options exist, specifically because these drugs carry risks of tendon rupture, nerve damage, and other serious side effects that aren’t justified for a simple bladder infection. Professional guidelines echo this: fluoroquinolones should be a last resort for uncomplicated UTIs, not a first choice.
UTIs During Pregnancy
Pregnant individuals need treatment even for UTIs that aren’t causing symptoms, because untreated infections raise the risk of complications. The American College of Obstetricians and Gynecologists recommends a longer treatment course of 5 to 7 days, compared to the 3- to 5-day courses used outside of pregnancy. Safe options include nitrofurantoin, certain penicillin-type antibiotics, sulfonamides (with timing restrictions), and fosfomycin. The choice depends on culture results and the stage of pregnancy.
UTIs in Men Take Longer to Treat
UTIs in men are almost always considered complicated infections because the anatomy makes simple bladder infections uncommon. When they do occur, treatment courses are longer. Current IDSA guidelines suggest 5 to 7 days of a fluoroquinolone or 7 days of another antibiotic for complicated UTIs that are responding well to treatment. If a prostate infection is suspected, which is common in men with fever or bacteria in the bloodstream, treatment often extends to 10 to 14 days. Shorter courses in men with febrile UTIs have been linked to lower cure rates, with one analysis finding microbiological cure dropped by about 14.5 percentage points when treatment was cut short.
What to Expect After Starting Treatment
Most people notice their symptoms, the burning, urgency, and frequent trips to the bathroom, begin improving within 24 to 48 hours of starting an antibiotic. That improvement doesn’t mean the infection is gone. Finishing the full course matters. With nitrofurantoin, that means all five days. With trimethoprim-sulfamethoxazole, all three. Stopping early increases the chance of the infection returning and contributes to resistance.
If your symptoms haven’t improved at all after two to three days, it could mean the bacteria causing your infection is resistant to the antibiotic you’re taking. A urine culture, ideally collected before you start treatment, can identify the exact bacteria and which drugs will work against it.
Preventing Recurrent UTIs
Some people deal with UTIs repeatedly, sometimes several times a year. Low-dose antibiotics taken daily at bedtime (typically nitrofurantoin at 50 to 100 mg) are one established approach to prevention. But long-term antibiotic use carries its own downsides, including the risk of building resistance over time.
A non-antibiotic alternative called methenamine hippurate has shown promise. It works by converting to formaldehyde in acidic urine, which inhibits bacterial growth. In a large trial of women who averaged seven UTIs in the prior year, those taking methenamine hippurate had about 1.4 UTI episodes over the following 12 months, compared to about 0.9 episodes in those on preventive antibiotics. That’s a meaningful drop from seven, even though antibiotics performed slightly better. For people who want to reduce their antibiotic exposure, it’s a reasonable option to discuss with a provider.