Fosfomycin is an antibiotic used to treat urinary tract infections (UTIs) and cystitis in women. That means it kills the bacteria responsible for causing the infection. It contains the active ingredient Fosfomycin trometamol, which is converted to Fosfomycin in the body to treat UTIs. It also prevents the cell walls of bacteria from being able to form, so they cannot multiply and continue causing infection.

Though cystitis can be caused by other things, it’s usually used to describe a bladder infection that can be irritating and painful. It is a type of urinary tract infection that is particularly common in women. Although it can get better on its own, antibiotics are sometimes needed to treat the infection.

Cystitis symptoms include:

• burning, pain, or stinging when going for a pee
• pee that looks dark, cloudy, or has a strong smell
• needing to pee more often than usual
• pain below your tummy

Fosfomycin works by killing the bacteria such as Escherichia coli that cause urinary tract infections, including cystitis. Most people notice an improvement in their symptoms within 2 to 3 days of taking Fosfomycin, but it is important to take the antibiotics as instructed even if you feel fine. If you don’t, there is a risk that the infection will return.

Fosfomycin is quickly absorbed in the body, so you should start to notice your symptoms improving quite rapidly.

How long does Fosfomycin last?

The active ingredient can remain in your urine for 36 hours or more after taking a single dose.

How long does Fosfomycin take to work?

Fosfomycin is usually prescribed in one single dose and works very quickly. Most people see an improvement in their symptoms within 3 days.

How effective is Fosfomycin?

Fosfomycin is considered a safe and effective treatment for UTIs and cystitis. In a study conducted in 2022, Fosfomycin cleared infection in 68.6% of participants with multidrug-resistant bacterial urinary tract infections.

To take fosfomycin, simply dissolve the contents of the sachet in a glass containing 50 to 75 ml of water and swallow immediately.

Always take fosfomycin exactly as it’s been prescribed by your doctor. Fosfomycin is supplied in 3g sachets and should be taken as a single dose.

When to take Fosfomycin

The best time to take it is before bed after emptying your bladder. Ideally, you should take Fosfomycin either 1 hour before or at least 2 hours after a meal.

You should try to take Fosfomycin on an empty stomach.

How much Fosfomycin to take

Fosfomycin is supplied in 3g single dose sachets. You should dissolve 1 sachet in a glass of water, between 50 and 75 ml, and take it as soon as it has dissolved. Always follow the advice of your doctor.

How long do you need to take Fosfomycin for?

Fosfomycin sachets are usually single doses. So, you only need to take one sachet, but you should follow the advice of your doctor if they recommend further doses.

You can buy Fosfomycin online from some UK registered pharmacies, including Superdrug Online Doctor. Fosfomycin requires a prescription for you to be able to buy it.

Can I buy Fosfomycin online?

You can buy Fosfomycin online from Superdrug Online Doctor. To order Fosfomycin you will need to:

• Fill in our brief online medical questionnaire.
• One of our doctors will review your answers to make sure the treatment is safe for you to use.
• Once approved, your order will be sent to an address of your choice in discreet packaging, or you can choose to collect it from your local Superdrug pharmacy.

You can message our doctors via your online patient account if you have any questions.

Can I buy Fosfomycin over the counter?

No, you will need a prescription from a UK-registered doctor to be able to buy Fosfomycin because it is a prescription-only medication (POM).

Can I get Fosfomycin on the NHS?

It may be possible to get Fosfomycin on the NHS, but you will need to consult your GP before getting it on the NHS.

Like all medicines, Fosfomycin may cause side effects but not everyone will get them.

Serious side effects

If you experience any of the following side effects you should contact your doctor straight away:

• a severe allergic reaction called anaphylactic shock. The symptoms may include a sudden onset of rash, itching, or hives, shortness of breath, difficulty breathing or wheezing
• a serious allergic reaction which causes swelling of the face, lips, tongue, or throat and breathing difficulties
• rapid heart beat
• mild to severe stomach cramps, blood in your poo or a high temperature (fever)

Common side effects

• headache
• dizziness
• indigestion
• infection of the female genital organs with symptoms such as inflammation, irritation and itching

Uncommon side effects

• diarrhoea
• feeling sick (nausea)
• being sick (vomiting)
• tummy ache
• skin rash
• tiredness
• tingling or numbness

Rare side effects

• itching

What to do if you get Fosfomycin side effects

If you experience side effects while taking Fosfomycin, speak to your doctor for advice. You can also report side effects directly to the Medicines and Healthcare products Regulatory Agency (MHRA) using their Yellow Card scheme.

Fosfomycin may not be right for everyone - certain conditions or certain medications can interact with Fosfomycin and make it less effective or potentially unsafe. You should tell your doctor if you have:

• an intolerance to some sugars
• ever experienced diarrhoea when taking any other antibiotics

You should also let your doctor know if you are or planning to get pregnant because Fosfomycin is not recommended for use during pregnancy. Because a small amount of Fosfomycin can pass into breast milk and affect your baby, it is important to tell your doctor if you are breastfeeding. Your doctor will tell you if it is safe for you to take Fosfomycin or if you should consider a different treatment.

Fosfomycin can cause dizziness which may affect your ability to drive or use machinery. If you experience dizziness or fatigue while taking Fosfomycin, you should avoid driving or using machines.

Contraindications

Fosfomycin should not be taken if you:

• are under 12 years old
• are allergic to Fosfomycin or any other ingredients in the medication
• have severe kidney problems
• are undergoing a procedure to clean and filter your blood if your kidneys are not functioning, called haemodialysis

Medications that interact with Fosfomycin

Before taking Fosfomycin, tell your doctor if you have recently taken or might take any other medicines, including herbal remedies. A medicine that is used to stop you from feeling sick called metoclopramide can affect Fosfomycin.

There are alternative antibiotics available to treat cystitis. At Superdrug Online Doctor, we provide MacroBid, an antibiotic treatment which contains the active ingredient nitrofurantoin. If you see your doctor, you may be prescribed alternative antibiotics, such as trimethoprim.

If you think you may have a urinary tract infection, including cystitis, you can order a TestCard UTI Test from Superdrug Online Doctor. It is a simple at-home test kit that works in a similar way to other testing strips or UTI dip tests you may have seen before, except this type uses an app on your phone to help doctors give you a quick and accurate diagnosis.

Fosfomycin vs Nitrofuratoin

Fosfomycin and nitrofurantoin are both effective treatments for urinary tract infections. Both are prescribed for recurrent infections but there is a difference in bacterial resistance. For example, bacterial resistance to nitrofurantoin is less common but the use of Fosfomycin should be limited to prevent the development of drug resistance by the infecting bacteria.

In a 2018 research study involving 513 women, nitrofurantoin was shown to cure UTIs after 28 days in 70% of patients compared to 58% of patients who used Fosfomycin. Prescribing guidance for doctors recommends that nitrofurantoin is the first choice treatment for UTIs in adults.