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Flashcards in penicillins 65/66 Deck (72):

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)

*can last 26 days!*


Penicillin G Benzathine + Penicillin G Procaine (Bicillin C‐R)

natural penicillin


natural penicillins are dispensed as ??


others dispensed by weight



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



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)

Antipseudomonal Penicillin (+B-lactamase inhibitors) combo bc of resistance
*broader spec. and more active against G- bacilli/mixed anaerobic/aerobic infections (Pseudomonas, Kleb) than carbenicillin or ticarcillin



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)
*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).



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.


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

(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*



*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

-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)