Term
Gram Positive Cell
murein layer = peptidoglycan layer or cell wall |
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Definition
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Term
Gram Negative Cell
lipoproteins help to keep the structure of the many layers |
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Definition
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Term
[image]
Gram +s have a more organized layer
Gram -s have a more random layer |
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Definition
| difference between the peptidoglycan layers of gram - and gram + bacteria |
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Term
2 daughter cells produced
sufficient metabolites necessary
once initiated, DNA synthesis must be completed
chromosome replication starts at membrane (where it is anchored); as bacterial membrane grows daughter chromosomes pulled apart |
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Definition
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Term
1) production of the basic building block (the UDP-acetylmuramyl-pentapeptide), takes place INSIDE THE CELL. Cycloserine, a rather toxic antibiotic that is employed rarely in the treatment of mycobacterial infections, inhibits the terminal reaction of the sequence. This reaction is the same in all bacteria. D-Ala/D-Ala is the same in all bacteria.
2) the precursor unit is carried from inside the cell membrane to outside. During this process a number of modifications occur in the chemical structure of the basic repeating unit. The repeating units are linked covalently to the preexisting cell wall. Vancomycin and bactracin act during this second stage.
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3) takes place entirely outside the cell membrane and consists of a variety of reactions that cross link and modify the wall components (the cross linking enzymes and some of the modifying enzymes are inhibited by penicillins and cephalosporins). Up to this point, all the building blocks were soluble. Once the TRANSPEPTIDATION reaction occurs they become insoluble and this makes them strong giving rigidity to the cell wall.
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[image] |
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Definition
| Stages of Cell Wall Synthesis |
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Term
NORMAL CONDITIONS
cell wall synthesis starts with autolysans that break BOTH THE GLYCOSIDIC BONDS AND PEPTIDE BONDS
then the new building blocks will come in between the breaks and go into the correct position
Next, transglycodases will form glycosidic bonds
Finally, transpeptidases form peptide bridges (peptide bridges make the cell wall very rigid)
WITH BETA LACTAM
cell must be actively dividing for beta lactams to work
opening of the cell wall after autolysans break glycosidic and peptide bonds
building blocks come in and transglycosidases form glycosidic bonds
but the transpeptidases are unable to build the peptide bridges because they are linked to a beta lactam
the cell will continue to grow but will not become rigid b/c no peptide bonds
SLIDES 17 AND 18 IN LECTURE 6 |
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Definition
| mechanism of cell wall synthesis (and what enzymes are involved) under normal conditions and with a beta lactam present |
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Term
NORMAL PATHWAY
first the enzyme carboxypeptidase will activate the D-Ala/D-Ala bond.
Then a serine transpeptidase will attacke the D-Ala/D-Ala bond. by attacking this bond one D-Ala will be lost and the serine will bind to the terminal D-Ala still attached
once it is linked, the enzyme (transpeptidase) works as an activator of the functional group. the functional group becomes very active and will be attacked by a nucleophile (glycine) --> peptide bridge is formed
WITH A BETA LACTAM
the serine transpeptidase will recognize penicillin and will interact with the penicillin molecule
the penicillin forms a COVALENT BOND with the serine transpeptidase that is very stable
the enzyme is trapped and is unable to form any peptide bridges
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Definition
| normal transpeptidase reaction and in the presence of a beta lactam |
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Term
D-Ala/D-Ala portion of the building blocks
[image]
the arrow is pointing to the beta lactam ring of penicillin and the amide bond in D Ala
This is why transpeptidases are inhibited by penicillin (because penicillin looks similar to their natural site of action) |
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Definition
| penicillin (and other beta lactams) have a similar structure to what in the synthesis of bacterial cell walls? |
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Term
| penicillin binding proteins (PBPs) or transpeptidases |
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Definition
receptors for beta lactam antibiotics
group of bacterial membrane bound enyzmes with active sites in the periplasmic space
form a covalent bond with beta lactams
have the ability to catalyze the rupture of the beta lactam antibiotics and to form a serine-linked penicilloyl enyzme
in general are species specific: S. pneumoniae and viridans streptococcal contain identical or closely related DNA sequences; high degree of homology of different enterococcal species
there are 2 groups: low and high molecular weights
relative affinities vary between beta-lactam antibioitcs |
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Term
| D-alanine carboxypeptidases |
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Definition
| hydrolized the bond between terminal D-alanine residues of cell wall units |
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Term
antibiotics that inhibit cell wall synthesis (like beta lactams) are usually bactericidal
cell wall autolytic enzyme activity is required for lytic death to occur
the growth of the cell require both autolytic and synthetic activity
the "unbalanced growth" hypothesis: inhibition of biosynthesis while continuing autolysis leads to weak points in the cell wall
the real mechanism may not be that simple and is not completely understood |
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Definition
| what is the killing effect of beta lactam antibiotics? |
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Term
beta lactams are active in the same way with both Gram - and Gram + bacteria. the difference between them is the location of the beta lactam target
the gram + cell envelope does not represent a significant barrier to the passage of small compounds
the Gram - cell envelope is considerably more complex: a secondary membrane is covalently linked via lipoprotein bridges to the peptidoglycan, and this outer membrane presents a physical barrier to the penetration of antibiotics
pores of gram - = porins: small HYDROPHILIC molecules can enter these pores
the role of the outer membrane can determine the spectrum of action of beta lactams |
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Definition
| what is the difference in the location of the beta lactam target for Gram - and Gram + bacteria? |
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Term
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Definition
plasmid or chromosomally encoded bacterial enzymes
catalizes the hydrolysis of the beta lactam C-N bond of beta lactam antibiotics
produced in a constitutive or inducible manner and secreted into the periplasmic space of gram - bacteria or into the outer medium of gram + bacteria
the most common mechanism of bacterial resistance to beta lactam antibiotics |
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Term
by acylating a serine at the active site of a beta lactamase
by using a water molecule coordinated to one or two zine (metallo beta-lacatmase) |
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Definition
| catalysis of beta lactam hydrolysis occurs by the addition of a water molecule via one of two mechanisms, depending on the structural type of enzyme: |
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Term
beta lactamases
changes in porins (for Gram -)
mutations in PBP (mainly in Gram +) |
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Definition
| 3 mechanisms of resistance to beta lactam antibiotics |
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Term
beta lactamases themselves are the targets for the inhibitory action of other beta lactam derivatives
the serine transpeptidase is involved in the biosynthesis of the peptidoglycan bond to penicillin and other beta lactam antibiotics making the antibiotics inactive
mechanism of the cyclic amide bond cleavage:
[image]
complex is formed between beta lactamases and penicillin
UNDER NORMAL CONDITIONS: PBP (transpeptidase) will recognize penicillin and form a covalent bond. the reaction is very stable and they do not come apart
RESISTANCE: beta lactams and beta lactamases also form a covalent bond BUT the enzyme is able to escape from the penicillin. the beta lactamase releases hydrolyzed penicillin (opened up beta lactam ring) which is inactive |
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Definition
| the serine beta lactamase recognition of beta lactam antibiotics |
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Term
Ser70 is the active site
Glu166 is strictly conserved within this family: its carboxylated side chain lies in the active site and interacts with other residues and with a molecule of water; its strategic position makes it an ideal candidate to play a critical role in the catalytic mechanism; it is involved in the deacetylation step (when the beta lactam is released); serves as an anchor to position it in the active site
a general base (proton abstractor) is presumed to participate in the active site (deacetylation)
[image]
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Definition
| mechanism of action of Class A beta lactamases |
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Term
are chromosomally encoded enzymes produced by Gram - bacteria
they hydrolyze many beta lactam antibiotics, including cephamycins and extended broad spectrum cephalosporins
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Definition
| mechanism of action of Class C beta lactamases |
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Term
sometimes called oxacillin hydrolyzing enzymes
mostly found in Enterobacteriaceae and P. aeruginosa
they usually confer resistance to amino- and ureidopenicillin and they posses high level hydrolytic activity against oxacillin, methicillin, and cloxacillin
their activities are weakly inhibited by clavulanic acid, but NaCl possesses strong inhibitory activity
2 serine residues in the active site (Ser67 and Ser115) both involved in hydrolysis: Ser 67 acts as a nucleophile in the acylation step of the reaction; Ser 115 is a key intermediary in proton transfer from the Ser67 to the substrate
Lys is positioned to act as a general base |
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Definition
| mechanism of action of Class D beta lactamases |
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Term
they are produced as extracellular or periplasmatic enzymes
all known representatives posses 2 conserved metal-binding sites and require zinc ions as enzymatic cofactors
all metallo beta lactamases identified are chromosomally encoded
they have the ability to function as carbapenemases
they utilize clavulanate and penicillanic acid sulfones
horizontal gene transfer
particular clinical threat -> broad substrate profile and expressed in combination with other beta lactamases
monozinc catalysis
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dizinc catalysis
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one zinc complexed with the carbonyl group and the other complexed with the N of the amide
neither situation forms a covalent bond but are able to open up the lactam an inactivate the beta lactam |
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Definition
| mechanism of action of Class B metallo beta lactamases |
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Term
same products in both acid and base degradations (the intermediates are different)
penilloic acid -> penilloaldehyde + penicillamine |
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Definition
| penicillins are unstable in both basic and acidic environments. What are the 3 degradation products of penicillins? |
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Term
R group: polar groups increase (broadens) spectrum to include Gram (-)
R group: electron withdrawing groups decrease the electron density on the side chain carbonyl and protects these penicillins in part from acid degradation
R group: the more lipophilic the side chain the more serum protein bound is the antibiotic
the carbonyl on the beta lactam ring is a must
no substitutions are allowed on position 5
the N at position 1 is required for activity
when the sulfur atom of the thiazolidine ring is oxidized to a sulfone or sulfoxide, it improves acid stability but decreases the activity of the agent
no substitutions allowed on the methyls, any change will lower activity, the methyl groups are necessary
the carboxylic acid of the thiazolidine is required for activity. if it is changed to an alcohol or an ester, activity is decreased
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Definition
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Term
polar groups: NH2, NO2, COOH, halogens, SO2R
electron withdrawing groups: NO2, halogens
lipophilic groups: alkyl, aryl, halogens |
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Definition
| examples of polar groups, electron withdrawing groups, and lipophilic groups. |
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Term
polar groups: no polar groups in the side chain, therefore it is narrow spectrum
EWG: nothing, therefore it is more susceptible to acid degradation. have to administer this drug IV b/c it is sensitive to stomach acid
lipophilic groups: yes, this drug is highly bound to plasma proteins
spectrum: primarily against Gram + cocci |
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Definition
analyze this structure according to polar groups, electron withdrawing groups, lipophilic groups.
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Penicillin G or benzylpenicillin |
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Term
polar groups: O adds very little polarity
EWG: ethers are electron withdrawing and this makes the drug more stable to acid than penicillin G
lipophilic groups: yes, plasma protein binding
can be administered orally
sensitive to penicillinases |
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Definition
analyze this structure according to polar groups, electron withdrawing groups, lipophilic groups.
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Penicillin V or phenoxymethyl Penicillin |
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Term
polar groups: yes, broader spectrum
EWG: yes, ethers are electron withdrawing so more acid stable (however, they are still unstable to gastric acid so must be administered via injection)
lipophilic groups: yes, protein bound
resistance to beta lactamases: yes, more resistant when there is steric hindrance that protects the amide from beta lactamses AND the key carbon is attached to an aromatic ring |
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Definition
analyze this structure according to polar groups, electron withdrawing groups, lipophilic groups.
image:297581|center}
methicillin and nafcillin |
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Term
generally less potent than penicillin G against Gram + microorganisms that produce beta lactamases but retain their potency against those that do
more acid stable: dicloxacillin > cloxacillin > oxacillin (due to EWG)
they are highly serum protein bound (not good for septicemia treatment) |
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Definition
analyze the structures according to beta lactamase resistance, electron withdrawing groups, and lipophilicity
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Term
polarity: more polar b/c of amino group in both and OH group in amoxicillin. increased hydrophilicity increases spectrum to include common Gram -
EWG: the addition of an amino group (electron withdrawing) in the side chain increases acid stability
beta lactamase sensitivity: tertiary carbon is good...but not enough to make a difference. the sensitivity against beta lactamases is overcome with the coadministration of additives (clavulanic acid, sulbactam) |
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Definition
analyze the structures according to polarity, electron withdrawing groups, and beta lactamase resistance
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Term
| prodrug: carboxylic acid must be free for the drug to be active |
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Definition
analyze this structure
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bacampicillin |
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Term
polarity: they preserve the anti gram + activity of ampicillin but higher anti gram - potency.
some strains of P. aeruginosa are sensitive to these penicillins
EWG: used PARENTERALLY in particular against Gram - bacteria
sensitive to beta lactamases, coadministration is advisable in the treatment of severe infections |
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Definition
analyze the structures according to polarity, electron withdrawing groups, beta lactamase resistance
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Term
polarity: the introduction of a side chain carboxyl enhances the anti gram - activity
susceptible to beta lactamases
EWG: unstable in acidic environment |
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Definition
analyze the structures according to polarity, beta lactamase resistance, EWG
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Term
Staphylococci do not produce beta lactamases that efficiently hydrolyze methicillin and other penicillinase resistant penicillins
MRSA are usually resistant to many antibiotics, including a number of antibiotics of widely differing structures and MOAs
MRSA remains sensitive to vancomycin
MRSA is usually determined by a chromosomal gene
the mechanism of resistance is believed to be acquisition of supplementary PBPs with low affinity for methicillin and other beta lactams
the gene encoding for this new PBP has also been found in some coagulase negative Staphylococci and can count for methicillin resistant in these organisms |
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Definition
| characteristics of methicillin resistant Staphtylococcus aureus |
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Term
the extent of protein binding ranges from 20-96%
the free drug passes rapidly into interstitial fluid and the peak concentration is achieved in abscess fluid and fibrin clots is about 20% of the unbound penicillin in serum
passage into cerebro-spinal, joint, and ocular fluids is poor in the absence of inflammation. in the case of inflammation, adequate concentrations are achieved
the penicillins pass into the bile to varying extents and in the absence of biliary obstruction most achieve levels in the bile that are equal to or significantly greater than the serum levels
the penicillins do not penetrate the prostatic fluids even with inflammation
a similar active transport system for organic acids exists in the choroid plexus. through this, penicillin can be transported from the cerebrospinal fluid into the blood
the cerebrospinal fluid levels are increased in the presence of inflammation both b/c of the rate of drug entry and b/c the active efflux is decreased
an active transport system in the eye carries organic anions from the intraocular fluids to the plasma, and probenecid prolongs the intraocular half life of penicillins |
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Definition
| distribution of the penicillins |
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Term
most of the penicillins are excreted in the kidney and within one hour. this rapid clearance is accomplished by secretion in the proximal tubule (80%) and by glomerular filtration (20%)
after an IM dose of penicillins, 80-98% of the drug is in the urine in the unaltered form
because of the renal excretion, the t1/2s of penicillins is significantly lengthened when renal function is impaired
the tubular secretion of penicillins is shared with a wide variety of organic acids. it used to be administered with probenecid (competition for the tubular transport) |
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Definition
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Term
penicillins have a high therapeutic index and are among the least toxic of all drugs
super-infections of the GI tract may occur during therapy with broad spectrum penicillins and antibiotic associated colitis occurs rarely
IM may be painful when large amounts of penicillins are administered. administration via IV may produce phlebitis
penicillins are usually salts (Na or K), and it should be considered especially for patients with compromised cardiac and renal function
in patients with renal failure, NEUROTOXIC reactions may occur
amp, carben, and oxacillin have been reported to cause occasional anicteric hepatitis characterized by transient elevations in hepatic enzymes
penicillin G and other synthetic penicillins occasionally cause reversible granulocytopenia |
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Definition
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Term
allergy is the most common type of ADR associated with penicillins and the penicillins are probably the most common cause of drug allergies
their onset may be immediate, accelerated, or delayed for several days or even weeks
less frequent in children than adults
manifestations of the allergy may be seen after any route of drug administration (anaphylaxis is less common with oral than parenteral)
incidence of anaphylaxis reactions appear to be higher in people with a history of atopy (asthma, hay fever, and other allergic diseases) |
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Definition
| hypersensitivity of penicillins |
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Term
before small molecules can elicit an immune response, they must become associated in an irreversible manner with large molecules in the host tissues
antibodies to the complete antigen is formed
the hapten may be the unaltered drug, a metabolite, or a chemical degradation product
penicillin itself is not the major form that acts as the hapten
[image]
penicillins undergo a ring cleavage (not the same cleavage as with beta lactamases or PBPs) in solution to form small amounts of several degradation products
D-benzylpenicillenic acid is a very reactive isomer of penicillin G, which can react irreversibly with sulfhydryl groups or amino residues in tissue proteins to form hapten-protein complexes
of primary importance is the chemically favorable reaction of D-benzylpenicillenic acid with the amino group of the Lysine residues of proteins |
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Definition
| immunochemistry of penicillin allergies |
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Term
skin testing: this is a classic method for testing hypersensitivity. not good for testing allergy to penicillins - intradermal injection of penicillin can precipitate a full blown anaphylactic response in the patient and the results are not completely reliable
a more reliable test substance has been developed from the antigenic determinant, a penicilloyl derivative of lysine (mimics the antigen itself): it is not immunogenic, its diffusion from the site of injection is slow, systemic response is rare, test is less dangerous, a positive test is not an absolute indication that the patient is allergic |
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Definition
| testing for hypersensitivity to penicillin |
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