Why Nitrofurantoin for Cystitis? The burning question!

We have changed to Nitrofurantoin(brand name Macrobid) as first line treatment for women with lower urinary tract infection (also called cystitis)due to the NICE (National Institute for Clinical Excellence) guidelines for women who do not have a catheter. It aims to optimise antibiotic use and reduce antibiotic resistance.(1)

Previously Trimethoprim was recommended as first line treatment but developing resistance to it’s effectiveness has meant that Nitrofurantoin may be the preferred choice. It depends on your geographical location and your kidney function.

PHE (Public Health England) have found that the number of urinary tract infections (UTIs) caused by drug resistant bacteria is increasing. One in three (34%) of the samples analysed were found to be resistant to Trimethoprim whereas only 3% of the UTI samples showed resistance to Nitrofurantoin.(2)

NICE have recommended that the first choice antibiotic for an uncomplicated urinary tract infection, UTI, be either Nitrofurantoin, if you are not suffering from reduced kidney function, or Trimethoprim  if there is a low risk of resistance to it where you live. (3)

There are AMR (Antimicrobial Resistance Indicators) local indicators that can give your doctor and yourself information on the effectiveness of any antibiotic. (4)

Antibiotic prescribing and antibiotic resistance are inextricably linked, as overuse and incorrect use of antibiotics are major drivers of resistance. The AMR local indicators are publicly available data intended to raise awareness of antibiotic prescribing. They can be used by your doctor to prescribe the most effective antibiotic appropriate for your infection.

We will offer Nitrofurantoin to women with cystitis but if Trimethoprim is deemed to be more appropriate by our doctor, using the AMR local indicators and other factors, then she will change it to Trimethoprim.

Why do we only treat women?

Urinary tract infection is more common in women and easier to treat than in men ; when it occurs in men they have to have the cause investigated and treated.

We only treat women with typical symptoms of cystitis when there is no concern that the infection has extended beyond the bladder. This is defined as acute simple cystitis. When there is concern that the infection has spread (eg when there is flank pain or other features suggestive of inflammation of the kidneys, fever and/or other signs of systemic illness including sepsis) we consider this to be a complicated UTI and needs referral to the GP.

However, Nitrofurantoin should not be used by women who have a reduced kidney function where their eGFR (estimated Glomerular Filtration Rate) is below 45(ml/min/1.73m ).

Most people are aware that their blood pressure and cholesterol numbers are important in knowing their risk for heart and blood vessel disease. Yet few know about their eGFR, one of the numbers that tells them about the health of their kidneys.

What is the glomerular filtration rate (GFR)?

When your kidneys are working well, they filter out wastes and excess fluid that become part of the urine your body makes each day. When kidneys aren’t working well, you do not remove enough wastes and fluids to keep you healthy. You also cannot make important hormones for your blood and bones. Your eGFR number is an estimate of how well your kidneys are working and keeping you healthy. If your eGFR number is low, your kidneys are not working as well as they should.

In adults, the normal eGFR number is more than 90. The eGFR declines with age, even in people without kidney disease.

How is kidney function measured?

A blood test called eGFR (estimated glomerular filtration rate) indicates roughly how well the kidneys are working to filter out waste from your blood. eGFR is reported in millilitres per minute and a normal eGFR is greater than 90 mL/min. eGFR is often shown as a percentage of normal and people find it useful to think of kidney function as a percentage, going from 100% (fully functioning) to 0% (no function). (5)

The table below indicates the various stages of chronic kidney disease (CKD)

Click to enlarge

Therefore, people with a moderate to severe loss of kidney function should not take Nitrofurantoin.

Our doctor will review your completed medical questionnaire for cystitis and decide which antibiotic is most appropriate for you.

References

1. https://bnf.nice.org.uk/drug/nitrofurantoin.html
2. https://assets.publishing.service.gov.uk/government/uploads/system/ uploads/attachment_data/file/656611/ESPAUR_report_2017.pdf
3. https://cks.nice.org.uk/urinary-tract-infection-lower-women#!scenario
4. https://fingertips.phe.org.uk/profile/amr-local-indicators
5. https://www.kidneyresearchuk.org/health-information/stages-of-kidney-disease

Author
Superintendent pharmacist Margaret Hudson BSc(Hons) MRPharmS
 12th September 2019