The most commonly prescribed antibiotics for an uncomplicated UTI are nitrofurantoin (a five-day course) and trimethoprim/sulfamethoxazole, often called TMP-SMX or Bactrim (a three-day course). A single-dose option called fosfomycin is also available. Which one your provider chooses depends on local resistance patterns, your kidney function, whether you’re pregnant, and whether you’ve had UTIs before.
First-Line Antibiotics for Simple UTIs
Guidelines from the American Academy of Family Physicians list five first-line options for uncomplicated UTIs in women:
- Trimethoprim/sulfamethoxazole (TMP-SMX): Taken twice daily for three days. This is one of the most widely used UTI antibiotics, but it’s only recommended when local bacterial resistance rates are below 20%. In many parts of the U.S., resistance has climbed above that threshold, so your provider may choose something else.
- Nitrofurantoin (extended release): Taken twice daily for five days. It works specifically in the urinary tract, which means it causes fewer disruptions to your gut bacteria compared to broader antibiotics.
- Trimethoprim alone: Taken twice daily for three days. This is essentially the first half of TMP-SMX without the sulfa component, which matters if you have a sulfa allergy.
- Fosfomycin: A single dose of 3 grams, taken once. The convenience is appealing, though it may be slightly less effective than multi-day courses for some infections.
- Pivmecillinam: Taken three times daily for three days. This option is more commonly prescribed in Europe and Scandinavia than in the U.S.
Most people notice symptom relief within one to two days of starting any of these, though you should finish the full course even if you feel better sooner.
Why Fluoroquinolones Are No Longer First Choice
Ciprofloxacin and levofloxacin (fluoroquinolones) are effective against UTI-causing bacteria, but the FDA has added a boxed warning, its strongest safety alert, to the entire class. The warning states that fluoroquinolones can cause disabling and potentially permanent side effects involving the tendons, muscles, joints, nerves, and central nervous system. For uncomplicated UTIs, the FDA’s position is clear: the serious risks generally outweigh the benefits when other treatment options exist.
That said, fluoroquinolones still have a role when first-line drugs can’t be used, for example, if you’re allergic to sulfa drugs and nitrofurantoin isn’t suitable for your kidneys. They’re also used more readily for complicated UTIs that have spread beyond the bladder.
What Makes a UTI “Complicated”
A simple, or uncomplicated, UTI is a bladder infection in an otherwise healthy person, typically a woman who isn’t pregnant. A UTI becomes complicated when there are factors that make it harder to treat or more likely to worsen. The Infectious Diseases Society of America’s 2025 guidelines focus on two key signals: fever (which suggests the infection has moved beyond the bladder, possibly to the kidneys) and point-of-care factors like abnormal vital signs or the presence of a urinary catheter.
Complicated UTIs require broader-spectrum antibiotics, often given intravenously at first if you’re seriously ill. The specific drug depends on how sick you are, your risk factors for drug-resistant bacteria, and local hospital resistance data. These decisions happen in a clinical setting and are guided by urine culture results rather than the empiric “best guess” approach that works well for simple bladder infections.
Kidney Function and Nitrofurantoin
Nitrofurantoin relies on your kidneys to concentrate it in the urine, which is where it does its work. If your kidneys aren’t filtering well enough, the drug won’t reach effective levels in the bladder and can build up in the bloodstream instead, raising the risk of side effects. The cutoff is a kidney filtration rate (eGFR) below 45: at that level, nitrofurantoin is generally not prescribed. For people with an eGFR between 30 and 44, a short course may sometimes be used cautiously, but only when other options aren’t suitable.
If you have chronic kidney disease or are older, your provider will likely check your kidney function before prescribing and may choose fosfomycin or TMP-SMX instead.
UTI Antibiotics During Pregnancy
UTIs are more common in pregnancy and more dangerous, because untreated bladder infections can progress to kidney infections, which raise the risk of preterm labor. The American College of Obstetricians and Gynecologists recommends treating UTIs in pregnant individuals with a 5 to 7 day course of antibiotics, longer than the typical 3 to 5 day course for non-pregnant adults.
Options considered safe in pregnancy include nitrofurantoin, certain penicillin-type antibiotics (beta-lactams), sulfonamides, and fosfomycin. Fosfomycin’s single-dose convenience makes it a practical choice during pregnancy. Your provider will base the final selection on a urine culture and sensitivity results rather than prescribing empirically, because getting the right drug matters more when two people are affected.
Preventing Recurrent UTIs With Low-Dose Antibiotics
If you get three or more UTIs in a year, or two within six months, you may be a candidate for preventive (prophylactic) antibiotics. The American Urological Association outlines two main approaches.
Continuous daily prophylaxis uses a much lower dose than a treatment course. Options include nitrofurantoin at 50 or 100 mg once daily, TMP-SMX at a fraction of the treatment dose taken daily or three times a week, or fosfomycin as a single 3-gram dose every 10 days. These regimens are typically maintained for several months and then reassessed.
If your UTIs are closely tied to sexual activity, a single low dose of an antibiotic taken right before or after intercourse can be equally effective. This approach uses the same drugs at similar low doses but avoids daily medication. Your provider will help determine which strategy fits your pattern of infections.
What Happens Before You Get a Prescription
For a straightforward UTI with classic symptoms (burning with urination, frequent urges, cloudy or strong-smelling urine), many providers will prescribe empirically based on your symptoms and a quick urine dipstick test. A full urine culture takes 24 to 48 hours to come back, so treatment usually starts before those results are available. If the culture shows the bacteria aren’t susceptible to the antibiotic you were given, your provider will switch you to one that matches.
This is why finishing your prescribed course matters even if symptoms improve. Stopping early can leave behind bacteria that are harder to kill next time, contributing to the resistance patterns that have already made some first-line drugs less reliable than they used to be.