Can Meropenem Be Administered Once Daily?
No, meropenem cannot be administered once daily for standard infections. Meropenem is a beta-lactam antibiotic with time-dependent killing and requires multiple daily doses to maintain therapeutic concentrations above the minimum inhibitory concentration (MIC) for adequate duration.
Pharmacokinetic Rationale Against Once-Daily Dosing
Meropenem has a short half-life of approximately 1 hour in healthy volunteers, which is characteristic of beta-lactam antibiotics 1, 2, 3.
Beta-lactam antimicrobials demonstrate time-dependent killing with only a brief postantibiotic effect, meaning they work best when drug concentrations remain above the MIC for extended periods rather than achieving high peak concentrations 1.
The efficacy of time-dependent antibacterial agents is related primarily to maintaining supra-inhibitory concentrations, making multiple daily dosing or continuous infusion more appropriate than once-daily administration 1.
Standard Dosing Recommendations
For most serious infections, meropenem should be administered every 8 hours at doses of 1-2 grams depending on infection severity and pathogen susceptibility 1, 4, 5.
The standard regimen is 1 gram IV every 8 hours for moderate infections and 2 grams IV every 8 hours for severe infections, pneumonia, or CNS infections 4, 6, 5.
Extended infusion over 3 hours is recommended for critically ill patients and when treating resistant organisms with MIC ≥8 mg/L to optimize pharmacodynamic targets 4, 6, 5.
Contrast With Once-Daily Antibiotics
Aminoglycosides, which show concentration-dependent killing and a prolonged postantibiotic effect, may be given once daily as this regimen offers therapeutic advantages and may reduce nephrotoxicity 1.
Ceftriaxone and ertapenem have sufficiently long half-lives (allowing serum concentrations above MICs for 12-24 hours) and thus can be given once daily 1.
Meropenem lacks these pharmacokinetic properties and cannot achieve adequate time above MIC with once-daily dosing 1, 3.
Special Dosing Considerations in Cystic Fibrosis
In cystic fibrosis patients with Pseudomonas aeruginosa infections, meropenem is dosed at 60-120 mg/kg/day divided into 3 doses (maximum 6 grams daily) or 60 mg/kg/day by continuous infusion 1.
Continuous infusion may be used but requires consideration of meropenem's limited stability at room temperature, typically requiring preparation of new infusion bags every 6 hours 1, 4.
Critical Pitfalls to Avoid
Never reduce the dosing frequency to once daily in an attempt to simplify administration, as this will result in subtherapeutic concentrations for most of the dosing interval and risk treatment failure 1, 6.
Do not confuse meropenem with ertapenem, which is the only carbapenem suitable for once-daily dosing due to its longer half-life 5.
In patients with renal dysfunction, extend the dosing interval rather than reducing individual doses below 1 gram for serious infections, but never extend beyond every 12 hours for standard infections 6, 2.
Optimal Administration Strategy
For critically ill ICU patients with normal renal function, higher daily doses should be used with consideration of extended or continuous infusion to maximize time above MIC 4.
Therapeutic drug monitoring is recommended in ICU patients to ensure adequate concentrations while avoiding neurological toxicity (target trough <64 mg/L) 4, 6.
The every-8-hour dosing schedule remains the cornerstone of meropenem therapy and should not be altered to once-daily administration regardless of clinical convenience considerations 1, 4, 5.