beta-lactam inhibitors - penicillin Flashcards
Vary in resistance to gastric acid
Vary in their oral bioavailability
Polar compounds
Not metabolized extensively
penicillins
penicillins are excreted unchanged or changed
unchanged
penicillins Excreted unchanged in urine via
Inhibited by probenecid
Glomerular filtration
Tubular excretion
Tubular excretion of penicillin is Inhibited by —
probenecid
Major antibiotics that inhibit cell wall synthesis
Penicillins
Cephalosporins
Partly excreted in bile
Ampicillin and nafcililin
penicillins are Derivatives of ?
6-aminopenicillanic acid
Plasma half-life of penicillins vary from –
30 min to 1 h
Given intramuscularly
Long half-lives
Drug is released slowly
Cross blood-brain barrier when meninges are inflamed
Procaine and benzathine penicillin G
penicillin inhibit cell wall synthesis by the following steps
- Binding of the drug to specific receptors (penicillin-binding proteins [PBPs]) located in the bacterial cytoplasmic membrane
- Inhibition of transpeptidase enzymes that act to cross-link linear peptidoglycan chains
- Activation of autolytic enzymes that cause lesions in the bacterial cell wall
? hydrolysis of the beta-lactam ring results in the lost of antibacterial activity
Enzymatic
Penicillinases
Formed by most staphylococci and gram (-) organisms
beta lactamases
Major mechanism for bacterial resistance
beta lactamases
Another mechanism of bacterial resistance
responsible for:
Methicillin resistance in staphylococci
Penicillin G resistance in pneumococci
Structural changes in target PBPs
Contribute to resistance by impeding access of penicillin to PBPs
Resistance in some gram (-) rods like P. aeruginosa
Changes in the porin structure in the outer membrane
3 types of resistance to penicillin
beta lactamases
Structural changes in target PBPs
Changes in the porin structure in the outer membrane
Prototype Narrow-spectrum penicillinase-susceptible agents
penicillin G
PENICILLIN G Prototype of narrow-spectrum penicillinase-susceptible agents Parenteral Limited spectrum of activity Susceptible to beta-lactamases
PENICILLIN G
For infections caused by Streptococci Meningococci Gram (+) bacilli Spirochetes
PENICILLIN G
Drug of choice for syphilis
Activity against enterococci is enhanced by aminoglycoside
PENICILLIN G
Oral drug
Oropharyngeal infections
PENICILLIN V
Very-narrow-spectrum penicillinase-resistant agents (3)
METHICILLIN (prototype), NAFCILLIN, OXACILLIN
Treatment of known or suspected staphylococcal infections
Methicillin-resistant S. aureus (MRSA) and S. epidermidis (MRSE) are resistant to other members of this subgroup and often to multiple antimicrobial drugs
METHICILLIN (prototype), NAFCILLIN, OXACILLIN
- Wider spectrum penicillinase-susceptible agents
ampicillin and amoxicillin
PIPERACILLIN and TICARCILLIN
Wider spectrum than pen G Susceptible to penicillinases Uses similar to pen G Enterococci L. monocytogenes E. coli P. mirabilis H. influenzae M. catarrhalis Enhanced activity in combination with inhibitors of penicillinases Synergistic (1+1=3) with aminoglycosides in enterococcal and listerial infections
ampicillin and amoxicillin
Activity against gram (-) rods
Pseudomonas
Enterobacter
Some cases of klebsiella species
Synergistic action with aminoglycosides
Susceptible to penicillinases
Enhanced activity in combination with inhibitors of penicillinases
PIPERACILLIN and TICARCILLIN
toxcity of penicillin
allergy
GI disturbances
toxcity of penicillin
allergy
GI disturbances
can cause neutropenia
Nafcillin
causes maculopapular rashes
Ampicillin
causes interstitial nephritis more than other penicillins
Methicillin
cross-allergenicity (complete or not)
Complete
GI disturbances are caused by
Oral penicillins especially ampicillin
specific GI disturbances
nausea and diarrhea
Pseudomembranous colitis
Maybe caused by (2)
direct irritation or by overgrowth of gram (+) organisms or yeasts
An antimicrobial drug that can eradicate an infection in the absence of host defense
mechanisms; kills bacteria
bactericidal
An antimicrobial drug that inhibits antimicrobial growth but requires host defense
mechanisms to eradicate the infection; does not kill bacteria
Bacteriostatic
Drugs with structures containing a beta-lactam ring: includes the penicillins, cephalosporins
and carbapenems. This ring must be intact for antimicrobial action
Beta-lactam antibiotics
Bacterial enzymes (penicillinases, cephalosporinases) that hydrolyze the beta-lactam ring of certain penicillins and cephalosporins
Beta-lactamases
Potent inhibitors of some bacterial beta-lactamases used in combinations to protect
hydrolyzable penicillins from inactivation
Beta-lactam inhibitors
Lowest concentration of antimicrobial drug capable of inhibiting growth of an organism in a
defined growth medium
Minimal inhibitory concentration (MIC)
Bacterial cytoplasmic membrane proteins that act as the initial receptors for penicillins and
other beta-lactam antibiotics
Penicillin-binding proteins (PBPs)
Chains of polysaccharides and polypeptides that are cross-linked to form the bacterial cell wall
Peptidoglycan
More toxic to the invader than to the host; a property of useful antimicrobial drugs
Selective toxicity
Bacterial enzymes involved in the cross-linking of linear peptidoglycan chains, the final step in
cell wall synthesis
Transpeptidases
Cross allergenicity with penicillins (complete, incomplete, partial) is assumed
Complete cross allergenicity must be assumed
T or F: 5-10% of patients with history of allergic rxns to penicillin will have the same rxn when given again
True