For advice on the diagnosis of UTI, see Urology Shared Clinical Guidelines. Only patients with signs and symptoms of urinary-tract infection require treatment with antibiotics (except in pregnancy). 

Note:  Asymptomatic bacteriuria (presence of bacteria in the urine without signs or symptoms of infection) occurs in 25% of women and 10% of men aged 65 years and over and is not associated with increased morbidity. Bacteriuria alone is rarely an indication for antibiotics. In the presence of a catheter, antibiotics will not eradicate bacteria. 

Narrow spectrum antibiotics for UTI include trimethoprim, nitrofurantoin and amoxicillin.  As a first generation cephalosporin, cefalexin has a reduced risk of infection with Clostridium difficile but has broader cover.  Avoid empiric use of quinolones except where indicated.  Review therapy once microbiological sensitivities are known and change to narrow spectrum agent where possible.  A decision aid for the diagnosis and management of suspected UTI in older people has been developed by the Scottish Antimicrobial Prescribing Group.

In pregnancy, short-term use of nitrofurantoin is unlikely to cause problems to the foetus (at term, theoretical risk of neonatal haemolysis).  Trimethoprim, as a folate antagonist, has a theoretical risk in first trimester in patients with poor diet or on another folate antagonist – manufacturers recommend avoiding in pregnancy.  Infection specialists may still recommend trimethoprim in pregnancy on an individual patient basis. See NHS Highland guideline: UTI Management in Pregnancy (NHS Highland intranet access required). 

Nitrofurantoin should not be used in severe renal impairment (eGFR less than 30mL/min) as it can result in toxic plasma levels and an effective drug concentration in the urine cannot be achieved.  Use with caution at eGFR levels between 30 and 45 mL/min in individual patients with resistant pathogens and limited treatment options where the benefit outweighs the risk.  Review regularly for clinical effectiveness.  It is unsuitable for treating upper urinary tract infection.  Alkalinising agents (such as potassium citrate) greatly reduce the efficacy of nitrofurantoin and should not be taken at the same time.

Trimethoprim and co-trimoxazole should be used with caution in severe renal impairment (eGFR less than 30mL/min).  Resistance to trimethoprim increases following the use of other systemic antibiotics as the resistance is often linked.  Monitor for clinical improvement if trimethoprim is used empirically after other antibiotics. Use either drug with caution with drugs that promote hyperkalaemia and monitor serum potassium levels if used for longer than 3 days.
Due to competition for renal secretion, serum creatinine may rise in any patient without change in glomerular filtration rate – use with caution in renal transplant patients as the rise can be difficult to interpret.

Discuss with Microbiology if there is high risk of, or previous infection/ colonisation with a VRE, ESBL producer, or other multi-resistant organism.  Due to the risk of infection following joint replacement, discuss the need for antimicrobial therapy with Microbiology.