Mechanism of Action and Spectrum of Activity
Meropenem belongs to beta-lactam antibiotics, representing a potent subgroup of carbapenems (alongside imipenem and ertapenem). Like other beta-lactams, it exerts a bactericidal effect by inhibiting bacterial cell wall synthesis.
The spectrum of activity of meropenem has important clinical features when compared with the "reference" drug imipenem:
- It demonstrates higher efficacy against Gram-negative flora.
- Its activity against Gram-positive cocci (staphylococci and streptococci) is somewhat lower than that of imipenem.
- Unlike ertapenem, which is inferior to other carbapenems against non-fermenting Gram-negative bacteria (Pseudomonas aeruginosa, Acinetobacter), meropenem maintains high efficacy in severe hospital-acquired infections.
Pharmacokinetics: Key Difference from Imipenem
Historically, the first carbapenem—imipenem (a derivative of thienamycin produced by Streptomyces cattleya)—has a serious pharmacokinetic drawback. In the renal tubules, it is rapidly degraded by a specific enzyme, dehydropeptidase I. Because of this, therapeutic concentrations of the antibiotic are not achieved in urine, and imipenem monotherapy is ineffective. This problem is overcome by combining imipenem with cilastatin (e.g., Tienam), an enzyme inhibitor that does not kill bacteria itself but protects the antibiotic.
The main advantage of meropenem is that its molecule is intrinsically resistant to renal dehydropeptidase I. Consequence: Meropenem is used as a standalone drug. It does not require cilastatin to maintain high concentrations in the body.
Indications and Administration
The drug is available as a powder in vials of 0.5 g and 1.0 g.
The route of administration is strictly limited: meropenem is administered intravenously only (as an infusion or bolus). Unlike ertapenem, there is no intramuscular formulation for meropenem.
- Standard dosing regimen: IV infusion of 0.5–1.0 g every 8 hours.
- Limitations: According to clinical data, meropenem is not indicated for bone and joint infections.
Side Effects and Safety
An important clinical advantage of meropenem over imipenem is its central nervous system safety profile. Meropenem lacks seizure-inducing activity, making it a safer choice for patients with neurological disorders or those at high risk of seizures.
Drug Interactions
When prescribing meropenem, two critically important interactions must be considered:
- Probenecid: co-administration increases plasma concentrations of meropenem.
- Valproic acid: all carbapenems (imipenem, meropenem, ertapenem) clinically significantly reduce serum valproate levels. This requires extreme caution when prescribing the drug to patients with epilepsy, as a sudden drop in anticonvulsant concentration can trigger a seizure.
Prescription Example
Example of a prescription for intravenous infusion of meropenem:
Rp.: Meropenemi 1,0 D.t.d. N. 10 S. Intravenously as an infusion, after dissolving in normal saline, every 8 hours.