What is the recommended dosage of ampicillin (Ampicillin) for the treatment of acute pyogenic meningitis?

Ampicillin Dosage for Acute Pyogenic Meningitis

For adults over 50 years or those with risk factors for Listeria (diabetes, immunosuppression, cancer), ampicillin should be administered at 2 grams IV every 4 hours as part of empiric therapy combined with ceftriaxone/cefotaxime plus vancomycin or rifampicin. 1

Age-Based Dosing Recommendations

Neonates (≤28 days postnatal age)

• Age <1 week: Ampicillin 50 mg/kg every 8 hours IV 1
• Age 1-4 weeks: Ampicillin 50 mg/kg every 6 hours IV 1
• Must be combined with cefotaxime or an aminoglycoside 1

Infants and Children (1 month to 18 years)

• Ampicillin is not routinely recommended in this age group unless Listeria is specifically suspected 1
• Standard empiric therapy is cefotaxime/ceftriaxone plus vancomycin or rifampicin 1

Adults 18-50 Years Without Risk Factors

• Ampicillin is not included in standard empiric therapy 1
• Use ceftriaxone 2g every 12 hours or cefotaxime 2g every 4-6 hours plus vancomycin or rifampicin 1
• Exception: If physician wishes to cover the rare possibility of Listeria (1.5% incidence), add ampicillin 2g every 4 hours 1

Adults ≥50 Years or <50 Years With Risk Factors

• Ampicillin 2 grams IV every 4 hours 1
• Combined with ceftriaxone 2g every 12 hours (or 4g every 24 hours) or cefotaxime 2g every 4-6 hours 1
• Plus vancomycin 10-20 mg/kg every 8-12 hours (target trough 15-20 μg/mL) or rifampicin 300 mg every 12 hours 1

Risk factors for Listeria include: diabetes mellitus, immunosuppressive drug use, cancer, and other immunocompromising conditions 1

Pathogen-Specific Dosing

Confirmed Listeria monocytogenes Meningitis

• Amoxicillin or ampicillin 2 grams IV every 4 hours 1
• Alternative: Co-trimoxazole 10-20 mg/kg (of trimethoprim component) in 4 divided doses 1
• Duration: 21 days 1
• Ampicillin plus gentamicin remains the treatment of choice for severe Listeria infections 2

Bacterial Meningitis (General)

• 150-200 mg/kg/day in equally divided doses every 3-4 hours for adults and children when ampicillin is indicated 3
• Treatment may be initiated with IV drip and continued with IM injections 3

Critical Implementation Points

Timing is paramount: Antibiotic therapy must be initiated within 1 hour of hospital arrival 1. If lumbar puncture is delayed for any reason (e.g., CT imaging), start empiric antibiotics immediately after drawing blood cultures 1.

Common pitfall: Do not use ampicillin monotherapy for empiric treatment of bacterial meningitis in any age group except neonates, where it must be combined with cefotaxime or an aminoglycoside 1. Third-generation cephalosporins are essential for pneumococcal and meningococcal coverage 1.

Dosing frequency matters: The every-4-hour dosing schedule for ampicillin in adults (2g q4h) provides superior CSF penetration compared to less frequent dosing 1. Adequate doses exceeding 6g/day are essential for effective treatment 2.

Dexamethasone consideration: Administer dexamethasone with the first antibiotic dose, but discontinue if Listeria is identified, as it is associated with increased mortality in neurolisteriosis 1.

Duration of Therapy

• Listeria meningitis: 21 days minimum 1
• Other bacterial meningitis: Continue for minimum 48-72 hours beyond symptom resolution or bacterial eradication 3
• Group A streptococcal infections: Minimum 10 days to prevent rheumatic fever or glomerulonephritis 3

Administration note: Use only freshly prepared solutions; potency decreases significantly after 1 hour of reconstitution 3. For IV administration, dissolve and administer slowly over 3-5 minutes for 250-500mg vials, or 10-15 minutes for 1-2g doses to prevent convulsive seizures 3.