Pharmacology of Carbapenems : Mnemonics

Commonly used Carbapenems

Mnemonic: MEDIC

1. Meropenem
2. Ertapenem
3. Doripenem
4. Imipenem/Cilastatin (renal dehydropeptidase I inhibitor)

Besides these, there are other drugs like tebipenem (1st oral carbapenem), panipenem, tomopenem (has MRSA activity), etc. which fall under carbapenems.

Coverage

As the name suggests, they have carbapenems attached to beta-lactam ring which provides protection against most beta-lactamases. They have good gram positive, gram negative and anaerobe coverage.

These are effective against beta-lactamase producing organisms like SPACE-M (cephalosporins are often ineffective in these):

1. Serratia
2. Pseudomonas aeruginosa; Proteus vulgarus, Providencia
3. Acinetobacter
4. Citrobacter
5. Enterobacter
6. Morganella

Ertapenem lacks good coverage against: APE organisms (hence, referred as gorilla-cillin as well).

1. Acinetobacter
2. Pseudomonas aeruginosa
3. Enterococcus

Some organisms are able to SPAM carbapenems and hence, do not work well with:

1. Stenotrophomonas maltophilia
2. Pseudomonas cepacia
3. Atypicals (Legionella, Chlamydica, Mycoplasma)
4. MRSA

These also do not effectively work against gram-negative bacteria that sometimes produce carbapenemase like Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii.

Mechanism of Action

These are beta-lactam antibiotics and work by interfering with bacterial cell wall synthesis, the details of which can be read in the post below. These are bactericidal antibiotic.

Pharmacokinetics

1. Renally excreted and require renal dosing
2. Imipenem requires cilastatin to decrease inactivation of drugs in proximal renal tubules
3. Half-life is ~1 hour except for Ertapenem which has a longer half-life of ~4 hrs (single dose per day may be sufficient)

Other points to be noted

1. All these lower seizure threshold and may cause seizure especially in patients with renal dysfuction.
2. Imipenem has the highest incidence of seizure.
3. Meropenem has a lower risk of seizures and hence, useful in cases of Meningitis.

Dr. Sulabh Kumar Shrestha, MS Orthopedics

He is the section editor of Orthopedics in Epomedicine. He searches for and share simpler ways to make complicated medical topics simple. He also loves writing poetry, listening and playing music.