penicillins 65/66 Flashcards
Penicillin G (Pfizerpen)
natural penicillin
parenteral admin (IV, IM)
only 33% absorbed after oral admin
60% plasma protein bound (ppb)
-active against many G+ and G-aerobic cocci (except strains producing penicillinase); most spirochetes; some G+ aerobic and anaerobic bacilli
-tend to be inactive against G- aerobic and anaerobic bacilli;
-Inactive against Mycoplasma, Rickettsia, fungi, viruses, and mycobacteria.
Penicillin V Potassium (generic)
natural penicillin
oral admin (used for less serious infections, less active than PCN G against most orgs, only for minor infections)
modified side chain (R=phenoxymethyl) more stable in stomach acid
oral dose gives plasma levels 2-5x higher then PCN G
50-70% ppb
Penicillin G Procaine (Wycillin)
natural penicillin
- used for S. pyogenes infections
- limited use for uncomplicated pneumococcal pneumonia or gonorrhea due to resistance
- injection can produce procaine reactions (bad taste, dizziness, palpitations, auditory and visual disturbances)
Penicillin G Benzathine (Bicillin L‐A, Permapen)
natural penicillin
- strep pharyngitis (1 dose vs 10 days PCN V)
- prophylaxis for RF from GAS (shot every 3-4 wks)
- syphilis
can last 26 days!
Penicillin G Benzathine + Penicillin G Procaine (Bicillin C‐R)
natural penicillin
natural penicillins are dispensed as ??
UNITS
others dispensed by weight
Methicillin
Penicillinase Resistant Penicillin ‐ Anti‐staphylococcal Penicillin
highly bound to plasma proteins (may result in clinical failure)
not used in US anymore
SE: intersitial nephritis
MRSA: usually also resist. to PCNs, ceph, amino glycosides, macrolides
40% ppb
Nafcillin
Penicillinase Resistant Penicillin ‐ Anti‐staphylococcal Penicillin
highly bound to plasma proteins (90% ppb!-may result in clinical failure)
-penetrates CNS, may be used for Staph meningitis
IV admin, inactivated in the acidic gastric environment and shows irregular oral absorption with or without meal
-excreted by liver
most resistant to
Staphylococcal B lactamases
eliminated by biliary excretion, don’t need to adjust the dose for pts with renal failure
Oxacillin (generic, Bactocil)
Penicillinase Resistant Penicillin ‐ Anti‐staphylococcal Penicillin
highly bound to plasma proteins (may result in clinical failure)
IV admin
excreted by liver
94% bbp!
eliminated by biliary excretion and by kidney, don’t need to adjust the dose for pts with renal failure?
Penicillinase resistants
implies more resistance to b-lactamases
Ampicillin (generic, Principen)
Extended Spectrum Penicillin (Aminopenicillin)
G+ AND G- coverage
can cause non-allergic skin rash
IV, oral absorption (40%, not as good as amoxicillin)
20% ppb
longer 1/2 life than PCN G
doses adjusted for renal failure
Amoxicillin (generic, Amoxil, Trimox)
Extended Spectrum Penicillin (Aminopenicillin)
G+ AND G- coverage
oral, good absorption (95%) in presence or absence of food, therapeutic plasma levels are obtainable with a lower dose
can cause non-allergic skin rash
20% ppb
longer 1/2 life than PCN G
doses adjusted for renal failure
Ticarcillin + Clavulanate potassium (Timentin); Ticarcillin (Ticar)
Antipseudomonal Penicillin (+B-lactamase inhibitors) combo bc of resistance
45% ppb
adjust for renal failure pts
-G- aerobic bacilli and mixed aerobic‐anaerobic infections (intra-abdominal, gene inf.)
(if Bacteroides, Ticar is alternative, metronidazole is preferred)
-pseudomonal infections (septicemia, UTIs) watch out for resistant strains which may arise
-may add an aminoglycoside (e.g. gentamicin)
SE: excess Na+, prolonged bleeding time
Piperacillin + Tazobactam (Zosyn); Piperacillin (Pipracil)
Ureidopenicillin
Antipseudomonal Penicillin (+B-lactamase inhibitors) combo bc of resistance IV *broader spec. and more active against G- bacilli/mixed anaerobic/aerobic infections (Pseudomonas, Kleb) than carbenicillin or ticarcillin
Aztreonam
B-lactam drug (other)
monobactam (monocyclic B-lactam ring- unique!)
poor oral absorption, admin parentally
excreted by kidneys, adjust dose for renal impairment
Imipenem + Cilastatin (Primaxin)
B-lactam drug (other)
carbapenem
broadest spectrum of activity
not absorbed orally
Clavulanic acid
B-lactam drug (other)
B-lactamase inhibitor
not much abx activity (always used in combo), needed to prevent breakdown from bacterial B-lactamase -most active against Amber class A B-lactamases, not good inhibitors of class C (B-lactam ring structure similar to amoxicillin; acts a suicide inhibitor of beta‐lactamase thus preventing the beta‐lactamse from breaking down amoxicillin).
Tazobactam
B-lactam drug (other)
B-lactamase inhibitor
not much abx activity (always used in combo), needed to prevent breakdown from bacterial B-lactamase -most active against Amber class A B-lactamases, not good inhibitors of class C
Amoxicillin + Clavulanic acid (Augmentin)
Combination products containing Beta lactamase inhibitor
good oral absorption
high levels in urine, does not penetrate CNS
excreted in kidney, adjust for renal impairment
Ticarcillin + Clavulanic acid (Timentin)
Combination products containing Beta lactamase inhibitor
Piperacillin + Tazobactam (Zosyn)
Combination products containing Beta lactamase inhibitor
core structure of PCNs
6-aminopenicillanic acid
B-lactam ring, Thiazolidine ring
(need intact rings for function!)
different pharmacokinetic, antibacterial props, different susceptibilities to breakdown based on R group
mechanism of B-lactam abx
bactericidal against bacteria that are actively growing by inhibiting bacterial cell wall synthesis
inhibit transpeptidase (PBP)–>inhibit bac cell wall synthesis–>lysis and killing of bacteria (activate autolysins)
ultimate death: activation of cell‐wall autolytic enzymes called autolysins (murein hydrolases) and bacterial cell lysis.
bacterial cell wall synthesis
net effect of this process is the production of glycan chains (alternating amino sugars; N-acetylglucoasamine and N‐acetylmuramic acid) that are cross‐linked by peptide chains
The final step in the production of the peptidoglycan cell wall is the complete cross‐ linking of the chains. This enzymatic process is accomplished by a transpeptidase enzyme located on the outside of the cell membrane.
B-lactam abx inhibit the ??
how can they do this??
transpeptidase enzyme and the subsequent production of a highly cross‐linked peptidoglycan cell wall
Penicillin covalently binds to the transpeptidase enzyme because there is a structural similarity between the penicillin molecule and the D‐alanyl‐D‐alanine end of the glycopeptide polymer (the normal substrate for the transpeptidase enzyme).
penicillins exert their bactericidal effect only on ??
actively dividing cells that are producing cell wall. Penicillins will have little or no effect on dormant bacteria or on microorganisms that lack cell walls. (not active against mycoplasma)
PCNs: good or bad selectivity??
good! humans do not have cell walls
PCNs are often used in combination with an ?? for a synergistic killing effect. Avoid ??
aminoglycoside antibiotic (e.g. gentamicin) Avoid in vitro mixing of penicillin family members with an aminoglycoside antibiotic in the same solution. (-/+-->deactivation)
mechanisms of bacterial resistance (one of the most important mechs for resistant to PCNs)
enzymatic destruction of PCN by bac enzymes:
B-lactamases break down B-lactam ring to yield inactive penicillin acid (> 300 B-lactamases have been ID’d)
-substrate for this enzyme (PCN) can induce production of this enzyme in bacteria (promotes resistance!!)
-G+ bac produce large amounts of B‐lactamases that get secreted outside of the bac (S. aureus)
-G- bac produce B-lactamases that are found between the outer and inner membranes. Since these ‐lactamases are located at the PCN site of action the bacteria have maximal protection against the drug.
another mechanism for abx-resistance
Structural differences in the PBPs (other than transpeptidase) (e.g. high molecular weight PBPs with low affinity for antibiotic).
example: highly PCN‐resistant Strep pneumo has 4 out of 5 PBPs with decreased affinity for PCN; Methicillin resistance in Staph is caused by the acquisition of a high molecular weight PBP via a transposon.
how to overcome resistance for orgs that have dec. affinity for PCN
give high dose PCN to compensate/overcome
yet another mechanism for abx-resistance
Inability of the PCN to penetrate to its site of action
in G- orgs: there is an OM that can function as a barrier to PCN. Small hydrophilic antibiotics can pass through the outer membrane through proteins called porins, which act as aqueous channels. Broader spec. abx and many cephs diffuse through these porins, but Penicillin G has difficulty passing through these porin channels.
also, efflux pumps can also pump drug out of the bacteria before the drug can act. (resistance mechanism in some G-bacteria)
examples: Pseudomonas can lack high permeability porins
P. aeruginosa, E. coli and N. gonorrhoeae – Active efflux
(G+ orgs: the peptidoglycan cell wall is near the surface of the bacteria. The PCNs easily penetrate to the outer layer of the cytoplasmic mem. and their site of action)
pharmacokinetics of PCNs
variable oral absorption, depends on acid stability and ability of food to dec. absorption
give 1-2 hrs before or after meal
except Amoxicillin absorption in presence or absence of food
also, for parental admin, IV is better than IM-may cause irritation
PCNs can bind to ?
plasma proteins and greater than 95% binding results in less free drug available to fight infection
PCN concentrations in most tissues are equal to serum, but have hard time penetrating some tissues like ??
however, during bacterial meningitis, ??
prostate, eye, brain
the BBB is disrupted (the meninges are inflamed) and PCN can pass into the brain (used for tx, about 5% plasma conc.)
PCNs rapidly excreted by ??
the kidneys
short half-life (30 min)
10% glomerular filtration
90% by tubular secretion (organic acid secretory mech)
adjust dose for many PCNs in renal failure and premies/infants who have dec. renal function
Example Dosing with Renal Impairment
(Creatinine Clearance 10 mL/min): Give 1/4th to 1/3rd of the normal dose.
?? can block tubular secretion, can be used to inc. plasma levels of PCN (can block transport out of CNS, again therapeutic strategy)
Probenicid (for gout)
some PCNs excreted mostly into ??
the bile
don’t need to be adjusted with renal failure, but LIVER failure
Nafcillin
Oxacillin
(test question)
the most adverse rxn to PCNs are
- hypersensitivity and allergic reactions*
- intact PCN and breakdown products can bind to host proteins and act as Ags for the production of anti-PCN-Abs
- may have anti-PCN Abs even if never received PCN (environmentally, i.e. milk)
- adults more susc. than children
- the major Ag determinant is degradation product Benzyl penicilloyl
?? administrations more commonly assoc. with hypersn rxns
Parenteral and esp. topical administration (don’t use topically bc of this)
more so than oral
if allergic to one PCN fam men, more likely to be allergic to others (1 exception, later)
-cross-allergic and cross-sensitizing, sensitization appears to occur in direct proportion to the treatment duration and total dose of PCN received in the past
most common allergic reaction are ??
type 1 (immediate) allergic reactions (1-72 hrs post admin)
IgE abs interact with PCN/PCN degradation products–>become fixed to mast cells of the skin, GI and RT–>release histamine and other vasoactive mediators upon reaction with sp. Ags–>may cause anaphylaxis, angioedema, and urticaria, rhinitis, asthma‐like symptoms, and laryngeal edema.
symptoms of T1 allergic rxn
skin rxns: rash, antioedema, urticaria, pruritis
GI manifestations: N/V/D ,abd. pain
respiratory tract involvement: dyspnea or wheezing
CV manifestations: hypotnsn, tachy, arrhythmias
*fatality is rare but when it occurs, usually due to laryngeal edema or CV collapse
T1 most common, but can cause other hypersensitivity rxns:
(TII: hemolytic anemia,
TIII: vasculitis,
TIV: interstitial nephritis, drug fever, contact dermatitis)
skin testing for PCN allergy
only useful for Type 1 hypersensitivity
Pre-Pen commercial product used for testing, contains benzyl penicilloyl (major Ag determinant) and polylysine (major Ag determinant)
+ test indicates individual is likely to have T1 immediate hypersn reaction to PCN
no commercial product of minor Ag determinants available for skin testing, but pharmacies at larger clinical sites usually can prepare a mixture of the minor Ag determinants
what to do if pt has bacterial endocarditis, etc. and will benefit from PCN but are allergic to it??
what other drugs should you have on hand??
desensitization protocol
15 min intervals btw dosing, increasing dose each time
get slow release of histamine from mast cells
at end of protocol, in therapeutic range
have anti-histamine, epinephrine, corticosteroids in case of allergic reaction
other adverse reactions to PCNs
- GI upset, N/V/D (large oral doses)
- superinfections due to PCNs killing off the NF (probiotics helps) i.e. pseudomembranous colitis, fungal infection
- high blood levels can cause seizures, so should not be injected DIRECTLY into the CSF (GABA antagonist affect in CSF if high enough blood concentration: at risk for drug interactions (Probenicid) and impaired metab/excr (renal failure))
serious Methicillin SE (no longer used in US anymore)
interstitial nephritis (nephron destruction and dec. renal function)
Type IV hypersensitivity reaction mediated by T-lymphocytes
other PCN adverse rxns: dispensed as K+ or Na+ salts, so problematic for ??
CHF and renal failure
Ampicillin, Amoxicillin SE
non-allergic skin rashes (1-28 days after tx) esp. if have viral infection (EBV)
diarrhea (more from ampicillin)
decrease effectiveness of OCTs
case: acute OM
what is the most likely causative organism?
how would you tx?
S. pneumo (35-40%) (definitely need to target: less likely to resolve on own)
Hib (30-35%)
Moraxella (15-18%)
-viruses may be the cause of 40-75%
tx if younger than 6 mos even if uncertain dx
tx 6 mo-2yr if certain dx, uncertain if severe illness
>2 yrs abx if certain dx and severe illness, otherwise observation
tx: Amoxicillin 80-90 mg/kg/day, s/s may not go away after initiating; may imply resistance
S. pneumo: involves PBPs
H. flu and M. cat involves B-lactamase
how tx this pt? Augmentin 90 mg/kg/day OR Ceftriaxone OR Clindamycin (not against G-)
if allergic to amoxicillin? Cephalosoprin (2/3) clarithromycin, azithromycin, clindamycin (no longer TMP-SMX, erythromycin + sulfisoxazole)
OM + effusion: does not need to be tx w. abx if
natural PCN spectrum of activity: G+
G+: non-resistant Staph and Streph 90% of S. aureus are resistant!: not good choice
- pneumococcal pneumonia: 25% resistant: until shown sensitive, use macrolide, FQ or 3rd gen. ceph (ceftriaxone)
- pneumococcal meningitis: usually sensitive, until known use 3rd gen ceph
- Strep pharyngitis: resistance not a problem
- Entercoccal endocardidtis: PCN G + aminoglycoside for synergistic effect
natural PCN spectrum of activity: G-
- can use for: anaerobes: activity against C. perfringes (gas gangrene) and C. tetani
- do NOT use for: N. meningitides, N. gonorrhea, Pasteurella Multocida (resistant): use 3 gen ceph instead
natural PCN spectrum of activity: other microorgs.
- spirochetes: Teponema pallidum (syphilis) parenteral PCN G is tx of choice!
- Actinomyces israelii
- do NOT use for: B. anthraces (resistance): use ciprofloxacin
PCN G procain and PCN G benzathine
IM injection in glut max or midlat thigh
do not inject into or near nerve: can result in permanent neuro damage
IM inj. provides slow release into blood and prolonged duration of action (repository forms)
-also provide local anesthetic effect (procaine, benzathine)
PCN G procaine (600,000 units) can last for several days
PCN G benzathine (1.2 million units) : 26 days! increase compliance
Penicillinase Resistant Penicillins
bulky side group (R group) makes them resistant to breakdown by Staphylococcal B-lactamases
Nafcillin the most!
do not need to adjust the dose for renal failure! may need to for liver failure
Penicillinase Resistant Penicillins spectrum
v. narrow window of activity
- less active than PCN G against PCN G susc. bac and anaerobes
- B-lactamase producing S. aureus: skin/ST infections, osteomyelitis, acute endocarditis
* not effective agains G- bac*
* beware of MRSA!*: use VANCOMYCIN or doxycycline
Extended Spectrum Penicillins (Aminopenicillins)
- able to penetrate G- outer membrane, better for G-s than PCN G*
- are susceptible to breakdown by B-lactamases
- can be combined with B-lactamase inhibitors
i. e. augmentin (Amoxicillin + clavulanate)
Extended Spectrum PCN mnemonic: HELPS ME
(see slide)
H. influenzae (Hib): URIs (sinusitis, otitis) (30-55% resistance, may use augmentin)
E. coli: UTIs (30-50% resistance)
L isteria mono: meningitis in immcompr. and in kids younger than 2 months, bacteremia
P roteus mirabilis: UTIs (10% resistance)
S almonell: typhoid fever, bacteremia, acute gastroenteritis (Ampicillin is an alternative to Salmonella and Shigella due to increasing resistance)
S trep pyogenes and PCN-susc Strep. pneumoniae, URIs
M oraxella Catarrhalis: RTIs, but around 100% resistance: use augmentin!
E nterococcus faecalis
Extended Spectrum PCNs SEs (amoxicillin, ampicillin)
decreased effectiveness of oral contraceptives
ethinyl estradiol: conjugated in liver to sulfate and glucuronide metabolites by intestinal bacterial enzymes–>conjugates excreted in bile
amoxicillin/ampicillin kills off flora that hydrolyze the ethinyl estradiol conjugates, so more ethinyl estradiol is reabsorbed
antipseudomonal PCNs
- effective against Pseudomonas (Ticarcillin more than Carbenicillin)
- also effective against PCN -resist. anaerobes (B. Fragilis)
- major use is in combo w. aminoglycoside for pseudomonal (or amp-resist. proteus) infections such as septicemia and UTIs
- used for mixed aerobic anaerobic infections (intra-abdominal)
- Prostatitis – Caused by E. coli, P. mirabilis, Enterobacter, Enterococcus
- NOT effective against most S. aureus infections
tox: high sodium, may interact w. platelets to prolong bleeding time, hypokalemia (Carbenicillin)
toxicity of Ticarcillin
high sodium can be problematic for pts w. CHF
-prolonged bleeding time
Piperacillin + Tazobactam uses
- often used in combo w. aminoglycoside for synergistic killing effect
- CAP: B-lactamase-producing H. flu or P. aeruginosa (+FQ, or + aminoglycoside + azithromycin, or aminoglygocoside + FQ)
- Nosocomial pneumonia: B-lactamase producing H. flu, Kleb, pseudomonas: empiric tx w. aminoglycoside (discontinue if pseudomonas is ruled out)
- serious G- infections: septicemia, burns, UTIs, OB/Gyn infections (E. coli), intraabdominal, skin/ST
Piperacillin + Tazobactam (Zosyn); Piperacillin (Pipracil) SEs
- less Na+ than Ticarcillin, better for pts w. CHF, heart failure
- less effect on bleeding time than Ticarcillin, better
Aztreonam SEs
patients allergic to PCNs appear NOT to react to Aztreonam
Carbapenems
wide spectrum of activity
imipenem broken down by dehydropeptidases in prox. tubule of kidney
-Cilastatin is compound that inhibits this enzyme and prev. breakdown of Imipenem, inc. renal concentration
-Meropenem, Ertapenem, Doripenem: resistant to breakdown, don’t need Cilastatin
- resistant to breakdown by most B-lactamases, (Trans configuration of the hydroxyethyl side chain). The metallo‐beta‐lactamases will inactivate carbapenems like Imipenem*
- eliminated by renal excretion, adjust dose w. renal failure
Carbapenem (imipenem) spectrum
how is it broad spectrum??
orgs active against?
> 90% of clinically important bacteria
- increased perm. thru porin channels in G- bacteria, resistant to B-lactamases, high affinity binding to PBPs
- G+ aerobes: strep (even PCN res. strains, staph (MSSA)
- G- aerobic bac (N. meningitidis and N. gonorrhoeae, Pseudomonas aeruginosa, Enterobacter)
- anaerobes: excellent activity against strict anaerobes, e.g. B. fragalis
- some potentially resistant bugs: MRSA, enterococcus faecium, C. diff
Carbapenem uses
- not for CA infections, reserved for serious HA inf., mixed aerobic/ana. inf (intraabd.)
- infections resistant to other PCNs
- add aminoglycoside for serious pseudomonas inf resistant to other B-lactam abx
Carbapenem SEs
- induction of B-lactamases : inc. resistant to other B-lactam abx (seen w. pseudomonas)*
- GI upset: N/V/D
- seizures (esp. Imipenem), esp. with renal failure,
- allergic (like other PCNs)
- bac/fungal superinfections
B-lactamase inhibitors
Clavulanic acid
sulbactam
Tazobactam
- little intrinsic antibac. on own, prevent degradation
- more active agains plasmid encoded b-lactamases vs. inducible B-lactamases
uses of Augmentin
(amoxicillin + clavulanic acid)
(S. aureus, H. flu, gonococci, E. coli M. catarrhalis)
-UTIs caused by resistant bacteria: E. coli, Kleb, enterobacter, P. mirabilis
-RTIs (ear and sinus): OM (drug of choice), sinusitis, S. pyogenes
-human and animal bite wounds : good activity against S. aureus and oral anaerobes (drug of choice)
-Gonorrhea: some success
Aztreonam uses
- highly resistant to breakdown by B-lactamases produced by G- bacteria*
- ONLY active against G- bac (like aminoglycosides): E. coli, Kleb, MDR Pseudomonas, S. marcescens, H. influenza, Enterobacter sp.
- septicemia, skin inf., intra‐abdominal and gene inf., bone/joint inf., Empiric therapy in febrile neutropenic patient (+ vancomycin for staph).
*used for G-infections when there is prior history of allergic reactions to beta‐lactam antibiotics. If the infection also has G+ involvement then another abx with G+coverage must be included
Imipenem specific uses
- Complicated UTIs
- Serious RTIs (e.g. S. aureus, S. pneumoniae, Enterobacter, E. coli, Klebsiella, S marcescens, Ps. aeruginosa involvement)
- Anaerobic/mixed aerobic‐anaerobic infections (e.g. peritonitis, intra‐abd, and gyne infections)
- Empiric therapy in Febrile neutropenic patients
- Other – skin/ST, bone/joint infections, septicemia
- NOT used for surgical prophylaxis
- NOT used for MRSA
- NOT to be used ALONE to treat serious Pseudomonas infections because of the possibility for selection of resistant microorganisms during therapy. (add aminoglycoside)
