Fosfomycin

About Fosfomycin

Fosfomycin is an antibiotic that blocks an early step in bacterial cell wall building and is concentrated in the urine. The label approves it for uncomplicated urinary tract infections (acute cystitis) in women caused by susceptible strains of Escherichia coli and Enterococcus faecalis. It is not for kidney infections (pyelonephritis) or an abscess around the kidney, and its safety and effectiveness in children 12 and under have not been established; the patient leaflet describes use from age 18. The whole treatment is one sachet: the granules are poured into 3 to 4 ounces (half a cup) of cold water, never hot water, stirred and drunk right away, with or without food. Symptoms usually improve within two to three days; if they do not, or if the infection returns, the prescriber chooses a different antibiotic rather than a second dose.

There is no boxed warning. Fosfomycin must not be taken by anyone allergic to it. Like other antibiotics it can lead to Clostridioides difficile diarrhea, which can be severe and has been reported two months or more after a course of antibiotics, so watery diarrhea with cramps or fever needs a call to the prescriber. Anaphylaxis has been reported after marketing. The most common side effects in trials were diarrhea, vaginal irritation, nausea and headache. The label has no adequate studies in pregnancy, so it is used only if clearly needed, and it is not known whether the drug passes into breast milk.

What is distinctive is that the entire course is one sachet, so the prescription is for a single item and there are no refills or missed doses to manage. Metoclopramide, and other medicines that speed stomach emptying, lower the amount of fosfomycin absorbed and passed into the urine, so they are not taken with it; cimetidine has no effect. The Monurol brand packages carry a marketing end date in 2023; the brand maker now sells the same sachet under the generic name as an authorized generic, and several other companies make generic sachets under FDA generic approvals. Fosfomycin is not a controlled substance.

Taking Fosfomycin

How to take it

Pour the whole sachet into 3 to 4 ounces (half a cup) of cold water, stir until it dissolves and drink it right away, with or without food; never use hot water. It is a single dose, and the prescriber should be called if symptoms have not improved in two to three days.

If you miss a dose

It is a single dose: take it as soon as you remember. If you are unsure whether you took it, ask the prescriber or pharmacist rather than taking a second sachet.

Storage

In the original sachet at room temperature, away from heat and moisture, out of reach of children, and not after its expiration date.

Interactions to know about

Metoclopramide and other medicines that speed the movement of the stomach and gut lower the amount of fosfomycin that reaches the urine; cimetidine does not affect it. Tell the pharmacist about every medicine you take.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Fosfomycin differs from pharmacy to pharmacy

A prescription is for a single sachet, so the quote is one item plus the dispensing fee, which is most of it. Not every pharmacy keeps fosfomycin in stock, and a pharmacy that orders it in may quote differently from one with a box on the shelf.

Every sachet is the same strength and form, and several makers supply it, so differences between quotes come from which maker the pharmacy buys from and whether the drug sits on a flat-price list rather than from the product itself.

Ways to pay less for Fosfomycin without insurance

• Ask the prescriber to write fosfomycin tromethamine generically; the brand name is no longer marketed and every pharmacy fills it with a generic sachet.
• Call ahead or ask more than one pharmacy whether it has fosfomycin in stock, since a bladder infection is treated the same day and not every pharmacy carries it.
• Ask whether the pharmacy has fosfomycin on a flat-price generic list.
• If no pharmacy near you stocks it, ask the prescriber whether another generic antibiotic for bladder infections would suit you; do not substitute on your own.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Fosfomycin

1. 1.How do I mix my fosfomycin sachet, and does it matter whether I eat first?
2. 2.What should I do if my symptoms have not improved after two or three days?
3. 3.Is my metoclopramide or any other medicine a problem with fosfomycin?
4. 4.Which symptoms after taking it, such as watery diarrhea or a rash, mean I should call my doctor?

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