Most uncomplicated urinary tract infections are treated with one of three first-line antibiotics: nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin. These oral medications clear the majority of bladder infections within 3 to 7 days. Which one you’re prescribed depends on local resistance patterns, your allergy history, and whether the infection is limited to your bladder or has spread to your kidneys.
First-Line Antibiotics for Bladder Infections
A straightforward bladder infection, the type that causes burning with urination and frequent trips to the bathroom, is typically treated with a short course of one of these medications:
- Nitrofurantoin is one of the most commonly prescribed options. The extended-release form is taken twice a day for 5 to 7 days. It works specifically in the urinary tract and has low resistance rates, which is a major advantage. Because it concentrates in urine rather than spreading throughout the body, it causes fewer disruptions to your gut bacteria than broader antibiotics.
- Trimethoprim-sulfamethoxazole (often called Bactrim or TMP-SMX) is another go-to choice, usually taken twice daily for 3 days. It’s effective and inexpensive, but resistance rates have climbed in many regions, so your provider may check a urine culture before prescribing it or choose a different option if resistance is common in your area.
- Fosfomycin has a unique advantage: it’s a single-dose treatment. You take one packet of granules dissolved in water, and that’s it. It’s slightly less effective than a full course of the other options, but the convenience makes it appealing when adherence to a multi-day regimen is a concern.
Other antibiotics like cephalexin and ceftriaxone are also used for simple UTIs, but they’re generally reserved for situations where the first-line options aren’t suitable.
Why Fluoroquinolones Aren’t First Choice
You may have heard of ciprofloxacin or levofloxacin for UTIs. These fluoroquinolone antibiotics are effective against urinary bacteria, but the FDA has placed a boxed warning on them, the agency’s most serious safety alert. They’ve been linked to disabling and sometimes irreversible side effects including tendon rupture, nerve damage in the hands and feet, and central nervous system effects like anxiety, depression, and confusion. These reactions can appear within hours to weeks of starting the medication and affect people of any age, even those without pre-existing risk factors.
The FDA’s guidance is clear: fluoroquinolones should not be used for uncomplicated bladder infections when other treatment options are available. They’re reserved for more serious infections where the benefits outweigh the risks.
Antibiotics for Kidney and Complicated Infections
When a UTI spreads beyond the bladder to the kidneys (pyelonephritis) or occurs alongside complicating factors like a catheter, urinary tract abnormalities, or a weakened immune system, treatment escalates. These complicated infections often require stronger antibiotics and longer courses.
For complicated UTIs without signs of sepsis, guidelines from the Infectious Diseases Society of America recommend starting with third- or fourth-generation cephalosporins, piperacillin-tazobactam, or fluoroquinolones. When sepsis is suspected, carbapenems may be added to the list of initial options. Many of these are given intravenously in a hospital or infusion center, at least initially, before transitioning to oral pills once improvement begins.
Treatment duration for complicated UTIs has gotten shorter in recent years. Current guidelines suggest 5 to 7 days of a fluoroquinolone or 7 days of another antibiotic for patients who are responding well, rather than the 10- to 14-day courses that were standard previously.
UTI Treatment During Pregnancy
UTIs are common during pregnancy, and untreated infections carry real risks including preterm delivery. The antibiotic options narrow because some drugs can affect fetal development. Nitrofurantoin, certain penicillin-type antibiotics (beta-lactams), sulfonamides, and fosfomycin are generally used, though the specific choice depends on the trimester and culture results. There’s no single “best” regimen established for pregnancy, so treatment is tailored based on what the urine culture shows the bacteria are sensitive to.
Pregnant women are also routinely screened for asymptomatic bacteriuria, bacteria in the urine without any symptoms. In non-pregnant adults this usually doesn’t need treatment, but during pregnancy it does because of the higher risk of progression to a kidney infection.
Side Effects to Watch For
Most people tolerate short courses of UTI antibiotics well, but each medication has its own profile of potential reactions.
Nitrofurantoin commonly causes nausea and stomach upset. Taking it with food helps considerably. In rare cases, especially with prolonged use, it can affect the lungs or nerves, but this is uncommon with the short courses used for bladder infections.
Trimethoprim-sulfamethoxazole has a longer list of potential reactions. Skin rash is relatively common. In rare cases, it can trigger severe skin reactions like Stevens-Johnson syndrome, a medical emergency involving widespread blistering and peeling. Signs to watch for include a spreading rash with red lesions that have purple centers, blistering of the skin or mucous membranes, or sores developing in the mouth. Dark urine, clay-colored stools, or yellowing of the skin or eyes can signal a liver problem.
Fosfomycin tends to be well tolerated, with diarrhea and nausea being the most frequent complaints.
Why Antibiotic Resistance Matters for UTIs
The bacteria causing your UTI, most often E. coli, may be resistant to one or more antibiotics. Resistance to older drugs like amoxicillin is widespread enough that it’s rarely used as a first-line UTI treatment anymore. Resistance to trimethoprim-sulfamethoxazole varies by region but has risen steadily in many communities.
This is why urine cultures matter. A culture identifies exactly which bacteria are causing your infection and which antibiotics will kill them. For a first, uncomplicated UTI, many providers prescribe empirically (based on what’s most likely to work) and only order a culture if symptoms don’t improve. For recurrent or complicated infections, cultures are essential to avoid wasting time on an antibiotic the bacteria have already learned to resist.
Nitrofurantoin and fosfomycin have maintained relatively low resistance rates compared to other options, which is one reason they remain preferred first-line choices. Finishing your full antibiotic course, even if symptoms improve within a day or two, helps prevent the surviving bacteria from developing resistance.
What to Expect During Treatment
Most people with uncomplicated bladder infections start feeling better within 1 to 2 days of starting antibiotics. The burning and urgency typically ease first, though you should finish the entire prescribed course. If your symptoms haven’t improved after 2 to 3 days on an antibiotic, the bacteria may be resistant to it, and your provider will likely switch medications based on culture results.
For kidney infections, recovery takes longer. You may feel significantly ill for the first few days, with fever, flank pain, and fatigue. Improvement on appropriate antibiotics usually begins within 48 to 72 hours. If you’re unable to keep oral medications down due to vomiting, or if you develop high fevers and signs of severe illness, intravenous antibiotics in a hospital setting may be necessary before transitioning to pills at home.