Fosfomycin Drug Interactions: What to Avoid and What to Tell Your Doctor

One of the advantages of fosfomycin (Monurol) compared to many other antibiotics is its relatively simple interaction profile. Because it is a single-dose treatment with a unique mechanism of action, it has fewer clinically significant drug interactions than multi-day antibiotics. However, there are several important interactions every patient should know before taking fosfomycin.

The Most Important Interaction: Metoclopramide (Reglan)

The most clinically significant oral fosfomycin interaction is with metoclopramide (brand name Reglan), a medication commonly prescribed for:

Nausea and vomiting

Gastroparesis (delayed stomach emptying)

Gastroesophageal reflux disease (GERD)

How it interacts: Metoclopramide speeds up stomach emptying, which reduces the time fosfomycin spends in the GI tract being absorbed. This significantly reduces fosfomycin's serum and urinary concentrations, potentially making it less effective at treating your UTI.

What to do: Tell your prescriber if you take metoclopramide. For a single-dose treatment like fosfomycin, your prescriber may recommend timing your doses to avoid this interaction, or they may choose a different antibiotic.

Live Bacterial Vaccines: A Contraindication

Fosfomycin, like all antibiotics, is contraindicated for concurrent use with live bacterial vaccines. The antibiotics can kill the live bacterial strains in the vaccine, preventing the vaccine from generating an immune response.

Affected vaccines include:

BCG (tuberculosis) vaccine

Cholera vaccine (oral)

Typhoid vaccine (oral)

You should wait until your antibiotic treatment is complete before receiving these vaccines. Given fosfomycin is a single dose, this is typically a short wait — but confirm the timing with your prescriber or pharmacist.

Other GI Motility-Increasing Drugs

The same mechanism that makes metoclopramide problematic applies to other drugs that increase gastrointestinal motility. These include certain laxatives and prokinetic agents. If you take any medication for digestive motility, mention it to your prescriber.

Oral Hormones and Estrogens: Minor Interaction

Like most antibiotics, fosfomycin may theoretically alter the intestinal bacteria that help activate certain oral hormones (estrogens, oral contraceptives). This is a low-risk interaction, and the clinical significance for a single-dose antibiotic like fosfomycin is considered minimal. However, if you are on oral contraceptives and are concerned, use a backup contraception method during and briefly after antibiotic treatment as a precaution.

Digoxin: Minor Interaction (Oral Formulations Only)

Oral fosfomycin may alter intestinal flora in ways that could slightly increase digoxin (a heart medication) levels. For a single-dose antibiotic, this is generally not clinically significant, but patients on digoxin should mention it to their prescriber.

IV Fosfomycin (Contepo) Has Additional Interactions

Note: the intravenous formulation of fosfomycin (Contepo) has more significant interactions, particularly with drugs that prolong the QTc interval (like amiodarone, azithromycin, and other QTc-prolonging agents). These QTc interactions apply to the IV formulation only — not to the standard oral Monurol packet taken at home.

What to Tell Your Doctor or Pharmacist Before Taking Fosfomycin

Before taking fosfomycin, tell your provider or pharmacist:

All prescription and over-the-counter medications you take, especially metoclopramide (Reglan)

Any upcoming live vaccine appointments (BCG, oral typhoid, oral cholera)

All vitamin, mineral, and herbal supplements

If you are pregnant or breastfeeding

If you have kidney problems (reduces clearance of fosfomycin)

Overall, fosfomycin has one of the most favorable interaction profiles of any UTI antibiotic — particularly relevant for patients with multiple drug sensitivities. For information on side effects to watch for, see: Fosfomycin Side Effects: What to Expect and When to Call Your Doctor