What antibiotics treat cystitis in the UK? 

In the UK, the choice of antibiotic for cystitis is guided by strict clinical protocols designed to target common bacteria like E. coli while minimizing the risk of antibiotic resistance. The National Institute for Health and Care Excellence (NICE) provides the framework that GPs and pharmacists use to select the most effective medication. While several options are available, the “first-line” choice usually depends on your medical history, any allergies, and local resistance patterns in your area. 

What We will cover in this Article 

• The two primary first-line antibiotics used in the UK 

• Why “short courses” are now the standard for simple cystitis 

• Second-line options and treatments for “complicated” infections 

• The role of laboratory sensitivity testing in medication choice 

• A data table of common antibiotics and their standard dosages 

• Guidance on managing side effects and completing the course 

First-Line Treatments: Nitrofurantoin and Trimethoprim 

For the majority of uncomplicated UTIs in women, UK clinicians prefer two specific antibiotics. These are chosen because they reach high concentrations in the urine, making them extremely effective at killing bacteria specifically within the bladder. 

Nitrofurantoin (Macrobid / Furadantin) 

Currently, Nitrofurantoin is the most common first-line choice in the UK. It is highly effective against E. coli and has a low rate of resistance. It works by damaging the DNA and proteins within the bacteria. Because it is absorbed quickly and concentrated in the bladder, it has a very high success rate for simple cystitis. 

Trimethoprim 

Trimethoprim was traditionally the go-to treatment for decades. However, in recent years, many bacterial strains in the UK have developed resistance to it. It is now typically only used if a urine culture confirms that the specific bacteria causing your infection are sensitive to it, or if Nitrofurantoin is not suitable for the patient. 

The Shift to Pivmecillinam and Fosfomycin 

As resistance to older antibiotics grows, UK guidelines have shifted to include newer or “reserve” options. These are often used when first-line treatments haven’t worked or if a patient has recurring infections. 

Pivmecillinam 

This is a type of penicillin that is specifically designed for urinary infections. It is increasingly being used as a first-line alternative in the UK because it is very effective against “Gram-negative” bacteria and has a lower impact on the “good” bacteria in your gut compared to other penicillins. 

Fosfomycin 

Fosfomycin is unique because it is usually given as a single, high-dose sachet that you dissolve in water. This is particularly useful for patients who struggle to remember to take tablets multiple times a day. It is often reserved for uncomplicated cases in women where other antibiotics are not appropriate. 

Comparison of UK Antibiotic Protocols 

The duration of the course is just as important as the type of antibiotic. In the UK, a 3-day course is standard for uncomplicated cystitis in women, while men and pregnant women usually require 7 days. 

Table: Common UK Antibiotics for Cystitis 

Antibiotic Name	Standard UK Dosage (Uncomplicated)	Course Duration (Women)	Common Side Effects
Nitrofurantoin	100mg (Modified Release) twice daily	3 Days	Nausea, dark urine (normal)
Pivmecillinam	400mg initially, then 200mg 3x daily	3 Days	Diarrhoea, stomach upset
Trimethoprim	200mg twice daily	3 Days	Rash, itchiness
Fosfomycin	3g (Single Sachet)	1 Dose	Headache, dizziness
Cefalexin	500mg twice daily	3-7 Days	Thrush (yeast infection)

Why “Best Guess” Prescribing Happens 

When you first see a GP or pharmacist, they will often give you an antibiotic based on what usually works for most people in your local area. This is known as “empirical” or “best guess” prescribing. 

If your infection is severe, recurrent, or if you are male, they will send a urine sample to the lab. Once the “sensitivity” results come back, the clinician may call you to change your antibiotic if the lab finds that your specific bacteria are resistant to the one you were first given. This ensures that the treatment is perfectly targeted to your infection. 

To Summarise 

The most common antibiotics for cystitis in the UK are Nitrofurantoin and Pivmecillinam, chosen for their effectiveness and low resistance rates. While short, 3-day courses are standard for most women, the treatment is tailored based on the individual’s risk factors. Completing the full course even if you feel better after the first day is essential for ensuring the bacteria are completely cleared and preventing the infection from returning. 

If you experience severe, sudden, or worsening symptoms, such as high fever, uncontrollable vomiting, or intense pain in your side or back, call 999 immediately. 

Authority snapshot 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with an MBBS and extensive experience in the NHS. Dr. Petrov has managed thousands of urinary infections in both primary care and emergency departments, ensuring that antibiotic choices follow the latest NICE and antimicrobial stewardship guidelines. This guide provides a clinical overview of the medications used in the UK to help the public understand their treatment pathways.