Monobactams and Carbapenims

Monobactams

Monobactams are the beta lactam drugs. One in clinical use is:

Aztreonam

• Monocyclic β-lactam ring
• Effective against aerobic gram – rods (esp. pseudomonas)
• Given I/V – 1-2 g/ 8 hourly
• Well distributed including CSF
• Can be given to penecillin-allergic patients

Adverse effects

1. Skin rash
2. Deranged LFTs

Uses

1. Pneumonia
2. Meningitis
3. Sepsis

Carbapenems

Beta lactam drugs. There are four drugs clinically available:

• Imipenem
• Meropenem
• Doripenem
• Etrapenem

Drug	Spectrum
Imipenem	Gram negative and positive bacteria anerobes E. faecium MRSA C. difficle
Meropenem Doripenem	more active against gram negative aerobes less active against gram +ve  microorganisms
Etrapenem	Same except less against pseudomonas aeruginosa and acinetobacter)

Pharmacokinetics

• These drugs are given I/V.
• Distributed to CSF along with other body compartments.
• Mainly renal excretion.
• Dose adjustment is done.
• Imipenem is metabolized in renal tubules by dehydropeptidase enzyme. Cilastatin is dehydropeptidase inhibitor, it may be combined so that enough drug reaches the site of action.
• Etrapenem is also given I/M. This process is usually painful so combined with 1% lidocaine to avoid pain.

Uses

1. Mixed aerobic / anaerobic infections especially by resistant strains.
2. Penicillin resistant pneumococci
3. Enterobacter infections
4. Extended-spectrum β-lactamase gram negative organisms
5. In patients with febrile neutropenia, combined with aminoglycosides.

Adverse effects

Adverse effects are more with Imipenem. Commonly seen are:

1. Nausea
2. Vomiting
3. Diarrhea
4. Skin rash
5. In patients of renal impairment, accumulations may lead to seizures
6. People allergic to penicillin are also allergic to these.