• Follow local guidelines when available.
• If local guidelines are not available:
• For an uncomplicated infection, prescribe either:
• Trimethoprim 200 mg twice daily, for 3 days, or
• Nitrofurantoin 50 mg four times daily, or 100 mg (modified-release) twice daily, for 3 days.
• For a complicated infection, prescribe a 5–10-day course of trimethoprim or nitrofurantoin.

Antibiotic treatment

• For women with urinary tract infection (UTI), there is evidence from a meta-analysis that antibiotics are more effective than placebo in eradicating bacteriuria and relieving UTI symptoms [Falagas et al, 2009].

Duration of antibiotic treatment

• A 3-day course of empirical treatment is recommended because there is good evidence from Cochrane systematic reviews that this achieves symptomatic cure in people with uncomplicated UTI; it is more effective than single-dose treatment and as effective as 5–10-day courses. This is also in line with recommendations from the Scottish Intercollegiate Guidelines Network (SIGN) [SIGN, 2006] and international guidelines [American College of Obstetricians and Gynecologists, 2008; European Association of Urology, 2009].
• For people with a complicated UTI, a longer course is recommended because there is evidence from a Cochrane systematic review that a 5–10-day course produced a higher bacteriological cure rate (but more adverse effects) than a 3-day regimen. The Cochrane systematic review concluded that a 5–10-day course may be considered for women in whom eradication of bacteriuria is important.

Route of administration

• The oral route is recommended, even for severe cystitis. A Cochrane systematic review found no evidence that oral antibiotic treatment is less effective than intravenous antibiotics for treating severe UTIs [Pohl, 2007].

Antibiotic choice: trimethoprim and nitrofurantoin as first-line options

• Trimethoprim and nitrofurantoin (both narrow spectrum antibiotics) are generally recommended as appropriate first-line antibiotics in the UK [SIGN, 2006; BNF 57, 2009].
• Narrow spectrum antibiotics are preferred over broad spectrum antibiotics such as co-amoxiclav, quinolones, and cephalosporins. This is in line with guidance issued by the Health Protection Agency which recommends avoiding the use of broad spectrum antibiotics when narrow spectrum antibiotics remain effective [HPA, 2009]. There are concerns that broad spectrum antibiotics increase the risk of Clostridium difficile, meticillin-resistant Staphylococcus aureus (MRSA), and resistant UTIs. Issues of antibiotic resistance are discussed below.
• Despite their widespread use, there are few comparative trials comparing these two antibiotics. There is evidence from four trials which found trimethoprim and nitrofurantoin to be equally effective and generally well tolerated.
• The dosages recommended are based on those recommended by the manufacturers of these antibiotics and are in line with doses used in trials [Goldshield Pharmaceuticals, 2002a; Goldshield Pharmaceuticals, 2002b; Actavis, 2007].

Bacterial resistance

• There are concerns that resistance to trimethoprim and nitrofurantoin is increasing, yet few data on the resistance patterns have been published.
• Evidence from older studies indicated trimethoprim resistance to be around 20–30% (although higher levels have been reported for certain parts of the UK) with a lower incidence for nitrofurantoin (less than 20%). However, these data should be treated with caution, because:
• Most of these studies were performed in the 1990s and resistance patterns may have changed.
• There are considerable geographic variations in antibiotic resistance pattern.
• It is difficult to compare results from different studies because of differences in populations (for example hospital or community) and differences in laboratory standards.
• Rates of clinical resistance to trimethoprim may be less common than expected from rates of resistance in laboratory samples. Statistics from laboratories are likely to be biased by higher proportions of samples from women with resistant infections [McNulty et al, 2006].
• Consequently, CKS recommends that, where available, local antibiotic guidelines should be followed, taking into account local resistance patterns.

Nitrofurantoin formulations

• Both immediate and modified-release formulations of nitrofurantoin are recommended because CKS found no evidence to prefer one formulation over another. For further information, see Dosage.