Lower UTI in Pregnancy

Comments from Expert Advisory Committee

  • Send MSU for culture.
  • Nitrofurantion should be avoided after 36 weeks due to risk of neonatal haemolysis.
  • Refer to local resistance patterns for empiric therapy where available and refer to MSU results. Amoxicillin resistance is common – only use if susceptibility data available.
  • Review empirical treatment with results of MSU culture and susceptibility.
  • Trimethoprim should not be prescribed for pregnant women with established folate deficiency, low dietary folate intake, or women taking other folate antagonists.
  • Note guidelines on Asymptomatic Bacteriuria in Pregnancy
  • If acute pyelonephritis is suspected, consider referral to hospital. Consider acute pyelonephritis/ upper UTI when:
    • Pain in the loin which radiates to the iliac fossa and suprapubic area.
    • Sudden onset general systemic disturbance with fever, rigors, vomiting.
    • Tenderness and guarding over the kidney.


Drug Dose Duration Notes

Nitrofurantoin Immediate Release Capsules

50mg-100mg every 6 hours

7 days


Avoid after 36 weeks due to risk of neonatal haemolysis.

Immediate/ Prolonged Release should be stated on the prescription (1see note below on formulation difference)




Nitrofurantoin Prolonged Release Capsules 100mg every 12 hours 7 days
Amoxicillin* 500mg every 8 hours 7 days *If known to be susceptible
2nd choice option
Cefalexin 500mg every 8 hours 7 days  
Alternative (if resistance to the above agents is suspected or if adherence to the above treatment course would be particularly problematic)







Single dose



Fosfomycin should only be used after a careful risk benefit assessment. Data in pregnancy is limited but to date has not indicated teratogenicity. Manufacturer advises that Fosfomycin should only be used during pregnancy, if clearly necessary.
Fosfomycin should ideally be taken at night, on an empty stomach, and empty bladder to maximise absorption and effectiveness.

*Seek specialist/microbiologist advice in case of severe penicillin allergy in pregnant patients if nitrofurantoin is not an option.

1Two nitrofurantoin formulations are available: nitrofurantoin immediate release capsules (Macrodantin®) and nitrofurantoin prolonged release capsules (MacroBid®). For the treatment of infection the prolonged release capsules are dosed twice daily whilst the standard capsules are dosed four times daily. These products are not interchangeable.

Patient Information

Safe Prescribing (visit the safe prescribing page)

Reviewed May 2022

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