Alternatives to Fosfomycin If You Can't Fill Your Prescription

You need to treat a urinary tract infection, but your pharmacy can't fill your fosfomycin (Monurol) prescription. Whether it is a stock issue at your local pharmacy, a cost barrier, or your insurance requiring step therapy, knowing your alternatives can make the difference between getting treatment today or waiting.

The good news: several other antibiotics are proven and guideline-recommended for treating uncomplicated UTIs. This guide walks you through the best alternatives to fosfomycin, how they compare, and what to discuss with your prescriber.

Before You Switch: Try to Find Fosfomycin First

If your pharmacy is out of stock, the medication may be available just a few miles away. Use medfinder to check which pharmacies near you have fosfomycin in stock before switching medications. This saves you the hassle of a new prescription and ensures you get the antibiotic your prescriber originally chose.

That said, if fosfomycin is genuinely unavailable, these alternatives are clinically sound options that your prescriber can switch you to quickly.

Alternative #1: Nitrofurantoin (Macrobid / Macrodantin)

Nitrofurantoin is the most clinically similar alternative to fosfomycin. Like fosfomycin, it concentrates specifically in the urinary tract and has minimal impact on the rest of your gut bacteria — meaning a lower risk of C. diff infection. It is also a first-line IDSA recommendation for uncomplicated UTIs.

Typical dose: 100 mg (Macrobid) twice daily for 5-7 days

Cash cost: Approximately $15–$40 with coupons for a full course

Pros: Widely stocked, low resistance rates (~1-2% for E. coli), safe in pregnancy, inexpensive

Cons: Multi-day course required; not suitable for patients with CrCl < 30 mL/min; not for pyelonephritis (kidney infection)

Alternative #2: Trimethoprim-Sulfamethoxazole (Bactrim / TMP-SMX)

Trimethoprim-sulfamethoxazole (TMP-SMX), commonly known by the brand name Bactrim, is one of the most widely prescribed UTI antibiotics in the world. It works by blocking two consecutive steps in bacterial folate synthesis — a powerful double-mechanism approach.

Typical dose: 1 DS (double-strength) tablet twice daily for 3 days

Cash cost: Very inexpensive — often $4–$8 with generic coupons

Pros: Short 3-day course, low cost, widely available, well-studied

Cons: Resistance rates exceed 20% in many U.S. regions; not for sulfa-allergic patients; can interact with blood thinners like warfarin; not recommended in pregnancy near delivery

Alternative #3: Cephalexin (Keflex)

Cephalexin is a first-generation cephalosporin antibiotic used as a second-line option for uncomplicated UTIs. It is typically prescribed when patients cannot tolerate first-line agents.

Typical dose: 500 mg twice daily for 7 days

Pros: Widely available, inexpensive, option for penicillin-sensitive patients with careful evaluation

Cons: 7-day course; higher E. coli resistance rates than fosfomycin or nitrofurantoin; broader spectrum affects more gut bacteria

Alternative #4: Ciprofloxacin (Reserved for Complicated UTIs)

Ciprofloxacin (a fluoroquinolone) is effective against UTIs but should generally be reserved for complicated infections, pyelonephritis, or patients who have failed other antibiotics. IDSA guidelines discourage using fluoroquinolones as first-line therapy for uncomplicated UTIs due to resistance concerns and a risk of serious side effects including tendon damage and C. diff.

How to Switch: What to Tell Your Prescriber

When calling your prescriber's office to request an alternative, be prepared to share:

The reason you can't fill fosfomycin (out of stock, insurance issue, cost)

Any allergies to sulfa drugs (which would rule out Bactrim)

Any kidney problems (which could affect nitrofurantoin eligibility)

Whether you are pregnant (affects which antibiotic is safest)

For more context on why fosfomycin can be hard to find, read: Why Is Fosfomycin So Hard to Find? [Explained for 2026]