We know that in women aged 15 to 55, Escherichia coli causes most UTIs (about 82 per cent), with Staphylococcus saprophyticus the next most common causal pathogen (about 11 per cent).4 This allows us to treat Angie’s symptomatic UTI empirically, without the need for a urine culture.1
Until recently, trimethoprim would have been the empirical antibiotic treatment for uncomplicated UTI. However, 2018 national data show that only around 73 per cent of about 88,000 urinary isolates of E. coli in New Zealand were susceptible to trimethoprim.5 Community laboratories from various regions within New Zealand (excluding Auckland) reported similar findings for 2022 data (77–83 per cent susceptibility – in about 27,000 isolates).6 Further, Auckland City Hospital laboratory susceptibility results from 2022 showed that only 68 per cent of 3757 E.coli isolates were susceptible to trimethoprim.7
By extrapolation, treatment of UTI with trimethoprim would therefore have approximately a one-in-four failure rate. It is not ideal for patient outcomes, or for healthcare providers’ workloads, if the patient has to return for further treatment. For socioeconomically disadvantaged people or those from rural areas, a repeat visit may be prohibitive.
In comparison with trimethoprim, sensitivity analyses have demonstrated that 99–100 per cent of E. coli and S. saprophyticus isolates in the community are sensitive to nitrofurantoin,5,6 and this antibiotic is presently recommended as first-line empirical treatment for uncomplicated UTI.1 Therefore, you recommend Angie takes nitrofurantoin.
The modified release nitrofurantoin 100mg formulation (Macrobid), funded since 2020, allows for more convenient twice-daily dosing compared with the four-times-daily dosing required with the older, immediate-release nitrofurantoin 50mg formulation (Nifuran). The advised duration of treatment with both preparations in Angie’s case is for five days only.8,9 A seven-day course is indicated in all men.1,8,9
Check the New Zealand Formulary8 or the Medsafe data sheet10 for contraindications and cautions to using nitrofurantoin, some of which are mentioned later, and for possible interactions with other medicines. Also discuss with Angie the behavioural approaches she can implement to try and avoid any further UTIs (see Panel 2).