Penicillins, Cephalosporins, and Other β-Lactam Antibiotics Flashcards
Β-lactam Antibiotics
Penicillins Cephalosporins Carbapenems
MOA of B-lactam antibiotics
inhibition of synthesis of the bacterial peptidoglycan cell wall
What is acylated by b-lactam antiobiotics?
the transpeptidase via cleavage of the –CO-N- bond of the B-lactam ring - Inhibit the transpeptidation reaction (last step in peptidoglycan synthesis - There are additional, related targets collectively known as Penicillin-binding Protein (PBP) – e.g. Transpeptidase
MECHANISMS OF BACTERIAL RESISTANCE TO PENICILLINS AND CEPHALOSPORINS
- Mutations -that decrease the affinity of PBPs for the antibiotic
- Acquisition of an additional high-molecular-weight PBP (via a transposon) with a very low affinity for all β-lactam antibiotics - Methicillin-resistant Staphylococcus aureus MRSA
- Inability of the agent to penetrate to its site of action
- Active efflux pumps remove the antibiotic from its site of action before it can act
- Destruction of antibiotics enzymatically via the action of β-lactamases - (4 classes: A to D)
- Microorganisms adhering to implanted prosthetic devices (e.g. catheters, artificial joints, prosthetic heart valves) -produce biofilms – produce extracellular polysaccharides – less sensitive to antibiotic
- Bacteria that survive inside viable cells of the host generally are protected from the action of β-lactam antibiotics.
MRSA MOA
Acquisition of an additional high-molecular-weight PBP (via a transposon) with a very low affinity for all β-lactam antibiotics
Highly active against Gram +
Penicillin G Penicillin V
Readily hydrolyzed by Penicillinase
Penicillin G Penicillin V
Ineffective against S. aureus
Penicillin G Penicillin V
First choice for treatment of penicillinase-producing S. aureus and S. epidermidis
Penicillinase-resistant Methicillin, Nafcillin, Oxacillin, Cloxacillin, Dicloxacillin (DMONC)
Antimicrobial activity against Gram – organisms (H. influenzae, E. coli & Proteus mirabiis)
Ampicillin, Amoxicillin + Clavulanate or Sulbactam (β-lactamase inhibitor)
Antimicrobial activity against Pseudomonas, Enterobacter, Proteus spp
Carbenicillin, Carbenicillin indantyl, Ticarcillin
Inferior to Ampicillin against Gram + cocci & Listeria monocytogenes
Carbenicillin, Carbenicillin indantyl, Ticarcillin
Less active than Piperacillin against Pseudomonas
Carbenicillin, Carbenicillin indantyl, Ticarcillin
Excellent antimicrobial activity against Pseudomonas, Klebsiella, & certain other Gram – microorganisms
Mezlocillin, Azlocillin, Piperacillin (MAP)
Retains activity of Ampicillin against Gram + cocci and L. monocytogenes
Mezlocillin, Azlocillin, Piperacillin (MAP)
Rheumatic Fever prophylaxis
Penicillin G - Gastric pH 2 – destroys antibiotic
More stable in acidic medium: Penicillin V or G?
Penicillin V
↓ tubular secretion of Penicillin ↑ plasma concentration
Probenecid
T/F: Penicillin G penetrates when meninges are inflamed
True
inhibits transport of Penicillin from CSF to bloodstream
Probenecid
Pneumococcal Infections
Penicillin G - agent of choice
Pneumococcal Pneumonia
3rd Generation CEPHALOSPORINS (Ceftriaxome) 20-24 M units of Penicilin G for 7-10 days
Pneumococcal Meningitits
Vancomycin + 3rd generation Cephalosporin 20-24 M units for 14 days of Pen G;
Streptococcal Pharyngitis
Pen V 500 mg q6 PO for 10 days
Scarlet Fever
Pen V 500 mg q6 PO for 10 days
S. Pyogenes (group A β-hemolytic Streptococcus) – cause RHD
Pen V 500 mg q6 PO for 10 days
Streptococcal Toxic Shock & Necrotizing Fascitis
Penicillin + Clindamycin
Streptococcal Pneumonia, Arthritis, Meningitis & Endocarditis (S. pyogenes)
Pen G 12-20M units IV 2-4 weeks Endocarditis: for 4 weeks
Streptococcus viridans
Pen G 12-20 M units IV Pen G for 2 weeks (4 weeks if alone) + Gentamycin 1mg /kg q8
Enterococcal endocarditis
Pen G/ Ampicillin + Gentamicin - Pen G 20M units or Ampicillin 12g IV + Gentamicin for 6 weeks
Meningococcal
Penicillin
Gonococcal
Ceftriaxone
Staphylococcal Infections MRSA
Penicillinase producing organism; resistant to Penicillin; Vancomycin, Linezolid, Daptomycin Trimethoprim-Sulfamethoxazole, Doxycycline, Clindamycin
10, 20 & Latent Syphilis < 1 year duration
Pen G Procaine 2.4M units/day IM + Probenecid for 10 days
Late latent syphilis, neurosyphilis, CV syphilis
Pen G 20M units for 10 days
Congenital Syphilis
Aqueous Pen G 50,000/kg in 2 divided doses or Procaine Pen G 50,000/kg OD for 10 days
Treatment for Jarisch-Herxheimer reaction
Aspirin - Therapy w/ Penicillin should NOT be discontinued
In Jarisch-Herxheimer reaction, Several hours after the 1st injection of penicillin manifestations
chills, fever, headache, myalgias, and arthralgias
Actinomycosis
Pen G
Diphtheria
Pen G -Pen G eliminates the carrier state Pen G 2-3M units/day for 10-12 days
Clostridial Infections (Gas Gangrene)
Pen G agent of choice as adjunct to antitoxin
Fusospirochetal Infection (Trench mouth)
Pen V 500mg q6
Rat-bite fever (Spirillum minor, Stretobacillus moniliformis)
Pen G – therapeutic agent of choice
Listeria monocytogenes
Pen G & Ampicillin + Gentamicin
Lyme disease : early disease
Tetracycline
Lyme disease: Severe
Pen g or 3rd gen cephalosporin
Penicillinase-resistant penicillins
Oxacillin, Cloxacillin, Dicloxacillin, Nafcillin
most active of the penicillinase-resistant penicillins
NAFCILLIN
Treatment of staphylococcal meningitis
NAFCILLIN
MRSA - resistant to:
Resistance to penicillinase-resistant penicillins & cephalosporins
MRSA: Hospital Acquired
resistant to aminoglycosides, tetracyclines, erythromycin, & clindamycin
MRSA: Community Acquired
resistant to macrolides Vancomycin (drug of choice) + Rifampin
MRSA: Drug of Choice
Vancomycin (drug of choice) + Rifampin
AMINOpenicillins
Ampicillin, Amoxicillin, & their Congeners
Enterobacteriacea (E. coli)
Ampicillin + Sulbactam (β-lactamase inhibitor) Amoxicillin + Clavulanate
Shigellosis
Amoxicillin less effective than Ampicillin for Shigellosis
Salmonella
Ampicillin high dose
Tx use of Aminopenicillin
- Upper Respiratory 2. UTI 3. Meningitis 4. Salmonella infection
ANTI-PSEUDOMONAL penicillins
Carboxypenicillins (Carbenicillin, Ticarcillin) Ureidopenicillins (Mezlocillin, Piperacillin)
supplied as disodium salt; CHF results from excessive Na+
Carbenicillin
Broadest antibacterial spectrum of the penicillins
Piperacillin + Tazobactam (β-lactamase inhibitor )
UNTOWARD REACTIONS TO PENICILLINS
- Hypersensitivity Reactions - Bone marrow depression - Granulocytopenia - Hepatitis (Oxacillin, Nafcillin) -Pain, Sterile Inflammatory reactions at IM site
first source isolated in 1948 by Brotzu from the sea near a sewer outlet off the Sardinian coast
Cephalosporium acremonium
Mechanisms of Bacterial Resistance: Cephalosporin
inability of the antibiotic to reach its sites of action * alterations in the penicillin-binding proteins (PBPs) – antibiotics bind to bacterial enzymes (β-lactamases) that can hydrolyze the β-lactam ring and inactivate the cephalosporin
2nd Generation Cephalosporin
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1st Generation
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3rd gen
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4th gen cephalosporin
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Carbapenems
- Imipenem
- Meropenem
- Doripenem
- Ertapenem
- Aztreonam
- Broader spectrum of activity
- Binds to Penicillin-binding Proteins
- Disrupts bacterial cell wall synthesis
- Death of susceptible microorganisms
- Very resistant to hydrolysis by most β-lactamases
β-LACTAMASE INHIBITORS
- CLAVULANIC ACID
- SULBACTAM
- TAZOBACTAM