Carbapenem Antibiotic Pregnancy: Use only if clearly necessary — limited human data

Meropenem (Multi-resistant Gram-negative Bone Infections)

Brand names: Meronem

Adult dose

Dose: 1–2 g IV every 8 hours

Route: Intravenous infusion over 15–30 minutes (or extended infusion 3 hours for MDR organisms)

Frequency: Every 8 hours

Max: 6 g/day (2 g every 8 hours for severe infections/MDR organisms)

Extended infusion (3-hour infusion of each dose) improves pharmacodynamic target attainment against organisms with raised MICs (MDR Gram-negatives). Reserve for MDR Gram-negative osteomyelitis, infected arthroplasty from ESBL-producing Enterobacteriaceae, or Pseudomonas aeruginosa resistant to ciprofloxacin. Always involve microbiology.

Paediatric dose

Dose: 10–40 mg/kg

Route: IV

Frequency: Every 8 hours

Max: 2 g every 8 hours (6 g/day) for severe infections

Paediatric MDR Gram-negative bone infection — under specialist guidance; neonates: 20 mg/kg every 12 hours

Dose adjustments

Renal

eGFR 26–50 mL/min: 1 g every 12 hours; eGFR 10–25 mL/min: 500 mg every 12 hours; eGFR <10 mL/min: 500 mg every 24 hours

Hepatic

No dose adjustment required

Paediatric weight-based calculator

Patient weight (kg)

Paediatric MDR Gram-negative bone infection — under specialist guidance; neonates: 20 mg/kg every 12 hours

Clinical pearls

Valproate interaction: CRITICAL — meropenem (and all carbapenems) inhibit renal tubular transport of valproate metabolites AND accelerate valproate glucuronidation, reducing serum valproate levels by 60–90% within 48 hours; epileptic seizures may occur; switch to alternative antibiotic or alternative antiepileptic
Extended infusion: for MDR organisms with MIC close to breakpoint, meropenem 2 g infused over 3 hours every 8 hours achieves better time above MIC than 30-minute bolus — requires stability data (meropenem is stable for 3–4 hours at room temperature)
Carbapenem stewardship: meropenem is a highest-category antibiotic in WHO AWaRe framework (Reserve category) — must involve microbiology or infectious disease; not for empirical use without clear justification
ESBL-producing Enterobacteriaceae (ESBL-E): meropenem is first-line for serious ESBL-E infections including ESBL osteomyelitis; cephalosporins FAIL despite susceptibility testing appearing sensitive in some ESBL strains
Penicillin cross-allergy: true cross-reactivity between penicillins and carbapenems is ~1% (based on shared beta-lactam ring); in anaphylaxis to penicillin, meropenem can usually be used with caution in supervised setting

Contraindications

Known hypersensitivity to carbapenems
Penicillin allergy with severe reaction (cross-reactivity ~1% with carbapenems — risk-benefit assessment required)

Side effects

Seizures — lower risk than imipenem; still occurs especially in renal impairment
GI effects — nausea, diarrhoea, C. difficile
Elevated LFTs
Hypersensitivity reactions
Thrombophlebitis at IV site

Interactions

Valproate — meropenem dramatically reduces valproate levels (up to 60–90% reduction); valproate seizures may occur; do NOT combine; use alternative antiepileptic
Probenecid — increases meropenem plasma levels (reduces renal tubular secretion)

Monitoring

Renal function and eGFR daily
Seizure activity
LFTs
Valproate levels if co-prescribed (and switch to alternative)
C. difficile toxin if diarrhoea develops

Reference: BNFc; BNF 90; IDSA Osteomyelitis Guidelines; WHO AWaRe Classification; MHRA Carbapenem-Valproate Interaction; SPC Meronem. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

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