Synopsis
Identify true bladder infection in men, obtain a useful culture and choose treatment that matches renal function and the anatomical site of infection.
- Afebrile dysuria and frequency can represent localised male cystitis, but ask specifically about flank pain, perineal pain, retention and systemic illness.
- Obtain a midstream urine sample for culture before the first antibiotic dose, then give immediate treatment for a clinically diagnosed lower UTI.
- For reliably excluded prostate involvement and eGFR at least 45, nitrofurantoin modified release 100 mg orally twice daily for seven days is a NICE option.
Key red flags
Rigors, flank pain, vomiting, hypotension, confusion or inability to pass urine demand urgent assessment for upper infection, sepsis or retention. A bladder-only drug cannot be relied upon for these syndromes.
Investigation priorities
Identify the organism and preserve useful susceptibility information.
Management branches
A thirty four year old has new dysuria and frequency without systemic symptoms.
- He is afebrile with normal observations, no flank or perineal pain, no retention or discharge, and no concerning sexual exposure. His eGFR is 88, he has no drug allergy or G6PD deficiency, and assessment supports isolated bladder infection.
- A midstream culture is collected and he starts nitrofurantoin modified release 100 mg orally twice daily with food for seven days. He receives a clear plan to seek urgent help for fever, rigors, flank pain or difficulty passing urine.
Key medicines
Nitrofurantoin modified release 100 mg capsulesGive 100 mg orally twice a day for seven days, with food or milk; this schedule is for the prolonged release formulation.Use the standard course only at eGFR at least 45 ml/min/1.73 m² and exclude pyelonephritis, systemic infection and suspected prostatitis. The 30–44 exception concerns selected short courses for resistant uncomplicated lower infection after benefit assessment. Do not give with G6PD deficiency, acute porphyria or hypersensitivity to nitrofurantoin, other nitrofurans or the formulation. Check urinary alkalinisers and magnesium trisilicate, which can reduce activity or absorption, and probenecid or sulfinpyrazone, which reduce renal excretion. Stop and assess new breathlessness, cough, jaundice or neuropathy; acute lung injury can occur in the first week.
Trimethoprim 50 mg per 5 ml oral suspensionAn alternative adult lower UTI regimen is 200 mg, equivalent to 20 ml of this suspension, orally twice daily for seven days.For this suspension, an eGFR of 15–30 ml/min, including exactly 30, requires the usual dose for three days then half the dose; below 15 use half the usual dose from the outset. Thus half of the stated adult dose is 100 mg, or 10 ml, twice daily. Dialysis use requires infectious-disease and renal supervision. Exclude hypersensitivity, severe hepatic insufficiency, megaloblastic anaemia and other blood dyscrasias. Stop immediately for a severe rash with blistering, mucosal lesions or systemic illness; never restart after trimethoprim-associated SJS, TEN or DRESS. Monitor renal function and potassium, especially with ACE inhibitors, angiotensin receptor blockers or potassium-sparing drugs. Avoid unsafe methotrexate combinations; review warfarin, phenytoin and digoxin, and check blood counts during prolonged treatment. A seven-day bladder course does not treat established chronic prostatitis.