Ampicillin Use for Urinary Tract Infections in Second‑Trimester Pregnancy

Recommended Oral Ampicillin Regimen

• For uncomplicated lower urinary tract infection (cystitis) in the second trimester, ampicillin 500 mg orally every 6 hours (total 2 g/day) for 3–7 days is an evidence‑based option when first‑line agents cannot be used. 1

First‑Line Therapy Preference

• Nitrofurantoin is the preferred first‑line agent for uncomplicated lower UTI in pregnancy, showing 79 %–99 % in‑vitro sensitivity against E. coli, the pathogen responsible for 75 %–86 % of pregnancy‑associated UTIs. 2
• The European Urology guideline recommends nitrofurantoin 100 mg orally every 12 hours for 5–7 days in pregnant women with uncomplicated cystitis. 2

Intravenous Ampicillin and Combination Therapy

• For uncomplicated UTI requiring IV therapy, ampicillin 18–30 g per day divided (commonly 2 g every 4–6 hours) is recommended. 1
• In hospitalized patients with pyelonephritis, ampicillin should be combined with an aminoglycoside (e.g., gentamicin 5 mg/kg once daily) to ensure adequate coverage. This recommendation follows the European Urology guideline. [3][4]

Treatment Duration

• Uncomplicated lower UTI should be treated for 3–7 days. 1
• Upper UTI (pyelonephritis) requires a longer course of 7–10 days. 2

Diagnostic and Monitoring Recommendations

• Obtain a urine culture before initiating antibiotics, but do not postpone therapy while awaiting results. 2
• Pregnancy itself increases the risk of progression from cystitis to pyelonephritis and of adverse maternal‑fetal outcomes; close clinical monitoring is therefore essential. 2

Antimicrobial Stewardship in Pregnancy

• Empiric antibiotic selection should be guided by local antibiogram data whenever available, as resistance patterns vary by region. 2