Tag: Carbapenem & Monobactum

Carbapenem & Monobactum

CARBAPENEM & MONOBACTUM

Q. 1

A diabetic patient developed cellulitis due to S. aureus, which was found to be methicillin resistant on the antibiotic sensitivity testing. All of the following antibiotics will be appropriate except ‑

 A

Vancomycin

 B

Imipenem

 C

Teicoplanin

 D

Linezolid

Q. 1

A diabetic patient developed cellulitis due to S. aureus, which was found to be methicillin resistant on the antibiotic sensitivity testing. All of the following antibiotics will be appropriate except ‑

 A

Vancomycin

 B

Imipenem

 C

Teicoplanin

 D

Linezolid

Ans. B

Explanation:

Ans. is ‘b’ i.e., Imipenem

Methicillin – resistant staphylococcus – aureus (MRSA)

.  Most staphylococci are penicillin resistant because they secrete penicillinase.

.   To overcome this resistance, penicillinase resistant penicillins, e.g. methicillin and nafcillin were developed.

.   MRSA is a strain of staphylococcus aureus that has acquired multi-drug resistance – even against methicillin and nafcillin (penicillinase resistant penicillin).

Treatment of S. aureus infections

.                         Sensitive to penicillin                  —> Penicillin G is the DOC.

.                         Pt. with penicillin allergy            —> Cefazoline is the DOC.

MRSA     —> Vancomycin is the DOC.

Methicillin – resistant staphylococcus – aureus (MRSA)

.                         Most staphylococci are penicillin resistant because they secrete penicillinase.

.                         To overcome this resistance, penicillinase resistant penicillins, e.g. methicillin and nafcillin were developed.

.                       MRSA is a strain of staphylococcus aureus that has acquired multi-drug resistance – even against methicillin and nafcillin (penicillinase resistant penicillin).

Treatment of S. aureus infections

.                         Sensitive to penicillin                  —> Penicillin G is the DOC.

.                         Pt. with penicillin allergy            —> Cefazoline is the DOC.

.                         MRSA                                            —> Vancomycin is the DOC.

.                         Other drugs for MRSA are

–                                                                                TMP – SMX                               – Levofloxacin                     – Linezolid                             –Tigecyclin

–                                                                                Minocyclin                                – Quinopristin                       – Daptomycin                       – Teicoplanin (KDT – 691)

– Ciprofloxacin                              – Dalfopristin                        – Oritavancin

.                         Adjunctive drugs (those that should be used only in combination with other antimicrobial agents) for M.R.S.A. are gentamycin, rifampin, fusidic acid.

“The carbapenem imipenem has excellent activity against methicillin – senstive S. aureus but not M.R.S.A.”


Q. 2

All have beta lactam ring EXCEPT –

 A

Penicillin

 B

Linezolid

 C

Cefotaxime

 D

Imipenem

Q. 2

All have beta lactam ring EXCEPT –

 A

Penicillin

 B

Linezolid

 C

Cefotaxime

 D

Imipenem

Ans. B

Explanation:

Ans. is ‘b’ i.e., Linezolid

beta-lactam antibiotics contain beta-lactam ring. These are penicillins, cephalosporins (e.g. cefotoxime), monobactams (aztreonam) and carbapenems (imipenem, meropenem).


Q. 3

True about imipenem is –

 A

It is a narrow spectrum antibiotic

 B

It is easily broken by beta lactam

 C

It can be used with cilastatin

 D

It is used with sulbactam

Q. 3

True about imipenem is –

 A

It is a narrow spectrum antibiotic

 B

It is easily broken by beta lactam

 C

It can be used with cilastatin

 D

It is used with sulbactam

Ans. C

Explanation:

Ans. is ‘c’ i.e., It can be used with cilastatin

o A limiting feature of imipenem is its rapid hydrolysis by the enzyme dehydropeptidase-I located on the brush border of renal tubular cells. Cilastatin is a reversible inhibitor of dehydropeptidase -1. It protects the imipenem from this enzyme.

o Carbapenems have the widest spectrum of all currently available antimicrobials, being bactericidal against most gram positive andgram negative aerobic and anaerobic pathogenic bacteria.

Quiz In Between


Q. 4

Aztreonam is a/an –

 A

beta-lactamase inhibitor

 B

beta-lactam antibiotic

 C

Antitubercular drug

 D

Antifungal drug

Q. 4

Aztreonam is a/an –

 A

beta-lactamase inhibitor

 B

beta-lactam antibiotic

 C

Antitubercular drug

 D

Antifungal drug

Ans. B

Explanation:

Ans. is ‘b’ i.e., beta -lactam antibiotic


Q. 5

Not true about aztreonam ‑

 A

f3-lactarn

 B

Monobactarn

 C

Active against pseudomonas

 D

Shows cross reactivity with other penicillins

Q. 5

Not true about aztreonam ‑

 A

f3-lactarn

 B

Monobactarn

 C

Active against pseudomonas

 D

Shows cross reactivity with other penicillins

Ans. D

Explanation:

Ans. is ‘d’ i.e., Shows cross reactivity with other penicillins

Aztreonam

  • It belongs to monobactams group of 13-lactam antibiotics.
  • It is active against gram negative organisms including pseudomonas, but has no activity against gram positive organisms or anaerobes fi-lactam antibiotic with aminoglycosides spectrum.
  • It is the only fi-lactam antibiotic that lack cross-reactivity with other P-lactam antibiotics, permiting its used in patients allergic to penicillins or cephalosporins.

Quiz In Between



Carbapenem & Monobactum

CARBAPENEM & MONOBACTUM


CARBAPENEM & MONOBACTUM

  • Are beta-lactam antibiotics.
  • Beta-lactam antibiotics – Drugs containing ßlactam ring in their structure.
  • Drugs:
    • Penicillins
    • Cephalosporins (above both discussed separately)
    • Monobactams e.g. aztreonam
    • Carbapenems e.g. imipenem

General features:

  • All ß-lactam antibiotics are bactericidal drugs.
  • MOA: 
    • Bind to specific receptors (penicillin-binding proteins; PBPs) on bacterial cell membrane.
    • Inhibits transpeptidase enzyme
    • Responsible for peptidoglycan chain cross-linking.
    • Bacteria formed in drug presence are without cell wall –> Dies due to water imbibition. (cell wall provides turgidity).

I) Monobactams:

  • Only beta-lactam antibiotic for patients with severe penicillin or cephalosporins allergy
  • Since not cross allergenic.
  • Drugs: Aztreonam.
    • Active against β-lactamase producing gram negative rods including Pseudomonas.
    • No activity against gram-positive organisms or anaerobes.
    • Administered i.v.
    • Prolonged half-life in renal failure.

II) Carbapenems:

  • Are β-lactamase resistant.
  • DOC for Enterobacter, Klebsiella & acinetobacter species.
  • Wide spectrum of activity – Including gram-positive cocci, gram-negative rods & anaerobes.
  • Only β-lactams, reliably efficacious against ESBL (extended spectrum β-lactamase) producing organisms.

Drugs: Imipenem, doripenem, meropenem & ertapenem.

Uses:

  • For Pseudomonas treatment:
    • Meropenem – Most active & Ertapenem – least.
    • Should be combined with aminoglycosides.

Individual drug description:

  • Imipenem:
    • Rapidly inactivated by renal dehydropeptidase I enzyme.
    • Always combined with cilastatin.
    • Increases imipenem half-life.
    • Inhibits nephrotoxic metabolite formation.
  • (Note on cilastatin: Inhibitor of renal dehydropeptidase I enzyme).
  • Adverse effects:
    • Imipenem-cilastatin combination include seizures & gastrointestinal distress (Main).
  • Meropenem, doripenem & ertapenem:
    • Not metabolized by renal dehydropeptidase.
    • Hence, less likely seizures.
  • Ertapenem:
    • Very long acting.
    • Inactive against Pseudomonas.
  • Loracarbef:
    • Chemically similar to cefaclor.
    • Oral drug.
    • Overdose can cause seizures.

Exam Important

  • Carbapenem & Monobactum are beta-lactum antibiotics.
  • Aztreonam is a Monobactam.
  • Imipenem is a Carbapenem.
  • All ß-lactam antibiotics are bactericidal drugs.
  • Monobactam is only beta-lactam antibiotic for patients with severe penicillin or cephalosporins allergy, since not cross allergenic.
  • Aztreonam is active against β-lactamase producing gram-negative rods, including Pseudomonas.
  • Carbapenem is β-lactamase resistant which is DOC for Enterobacter, Klebsiella & acinetobacter species.
  • Carbapenem is only β-lactams, reliably efficacious against ESBL (extended spectrum β-lactamase) producing organisms.
  • Imipenem, doripenem, meropenem & ertapenem are all carbapenem.
  • Meropenem is a most active & Ertapenem is least active carbapenem.
  • Imipenem is always combined with cilastatin because it gets rapidly inactivated by renal dehydropeptidase I enzyme.
  • Cilastatin is an inhibitor of renal dehydropeptidase I enzyme.
  • Imipenem-cilastatin combination mainly causes seizures & gastrointestinal distress (adverse effects).
  • Meropenem, doripenem & ertapenem are not metabolized by renal dehydropeptidase, hence, less likely seizures.
  • Ertapenem is very long-acting & are inactive against Pseudomonas.

 

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