Rantoin SR 100 mg Capsule

Urinary antibacterial for:

• Acute uncomplicated lower urinary tract infection (cystitis) — first-line in many guidelines
• Prevention of recurrent urinary tract infections (low dose at night)

Acute cystitis (adults): modified-release 100 mg twice daily (or immediate-release 50 mg four times daily) for 3 days (women) to 7 days (men, pregnancy).

Prevention: 50–100 mg at bedtime.

Children over 3 months: 3 mg/kg/day in 4 divided doses for 3–7 days; prevention 1 mg/kg at night.

• Take with food or milk (better absorption, less nausea).
• Not effective for kidney infections (pyelonephritis) or when kidney function is poor.

• eGFR below 45 ml/min (short courses may be used down to 30 with caution)
• G6PD deficiency (haemolysis)
• Infants under 3 months; pregnancy at term (38–42 weeks), labour and delivery
• Acute porphyria
• Allergy to nitrofurans

Common: nausea, loss of appetite, headache, dark yellow/brown urine (harmless).

Less common: vomiting, diarrhoea, dizziness, rash.

Rare but serious: acute lung reactions (fever, cough, breathlessness — within days) and chronic lung fibrosis with long-term use; liver injury (hepatitis); peripheral neuropathy (tingling, numbness — especially kidney impairment, diabetes); haemolytic anaemia; severe allergic reactions.

• Long-term prophylaxis: monitor lungs and liver; stop if cough, breathlessness or tingling develops.
• Elderly, kidney impairment, diabetes, B12/folate deficiency, anaemia: higher risk of nerve damage.
• May give false-positive urine glucose tests.

May be used in pregnancy except near term (38 weeks onwards) — risk of haemolysis in the newborn. Avoid breastfeeding infants under 1 month or with G6PD deficiency.

• Magnesium trisilicate antacids (reduce absorption)
• Probenecid, sulfinpyrazone (reduce urinary levels, increase toxicity)
• Quinolones such as nalidixic acid (antagonism)

Vomiting. Supportive care, fluids to promote excretion.

Store below 30°C, protected from light.