Beta-lactam antibiotics:...

27
MEDCH 561P Beta-lactam antibiotics: Penicillins http://botit.botany.wisc.edu/toms_fungi/nov2003.html April 15, 2013 Kelly Lee, Ph.D. H-172J [email protected] Penicillium chrysogenum + Staph. Aureus

Transcript of Beta-lactam antibiotics:...

MEDCH 561PBeta-lactam antibiotics: Penicillins

http://botit.botany.wisc.edu/toms_fungi/nov2003.html

April 15, 2013Kelly Lee, Ph.D.

[email protected]

Penicillium chrysogenum + Staph. Aureus

D-alanyl-D-alaninepenicillin nucleus (6-APA)

Beta-lactams bind to transpeptidase in place of D-Ala-D-Ala

Transpeptidase (a PBP) normally binds to the D-Ala-D-Ala at the end of peptidoglycan precursors to crosslink the peptidoglycan. Beta-lactams such as penicillin mimic D-Ala-D-Ala, occupying the PBP active site and inhibiting crosslinking of peptidoglycan peptide bridges. Cell wall is weakened and this allows autolytic enzymes that degrade the peptidoglycan network to dominate, leading to lysis of the cells. Bactericidal.

Beta-lactams bind to transpeptidase in place of D-Ala-D-Ala

L-Ala

D-Glu

L-Lys Gly Gly Gly Gly Gly

L-Ala

D-Glu

L-Lys Gly Gly Gly Gly Gly

ONAM NAGO NAM NAGO

D-Ala

D-Ala

D-Ala

D-Ala

Gly

5Gly

5

L-Ala

D-Glu

L-Lys

L-Ala

D-Glu

L-Lys

Gly Gly Gly Gly

L-Ala

D-Glu

L-Lys

L-Ala

D-Glu

L-Lys

ONAM NAG

ONAM NAG

O

Gly

5

ONAM NAGO NAM NAGO

D-Ala

D-Ala

D-Ala

D-Ala

D-Alatranspeptidase active site is occupied by beta-lactam and cannot bind D-Ala-D-Ala, thus crosslinking does not take place

bactericidal, provided bacteria is susceptible

beta-lactam

Beta-lactam antibioticsAmoxicillin (penicillin) Cephalexin (cephalosporin)

Imipenem (carbapenem) Aztreonam (monobactam)

Beta-lactam antibiotics

๏ Penicillins๏ Potent, safe, but alone generally narrow spectrum, and susceptible to beta-

lactamases, allergy

๏ Cephalospirins๏ Less susceptible to penicillinases, less allergenic, broader spectrum in later

“generations” (increased Gram- coverage)

๏ Carbapenem๏ IV, broad spectrum, resistant to most beta-lactamases; drugs of last resort

๏ Monobactam๏ IV, Gram- coverage (poor for Gram+), resistant to many beta-lactams

Penicillins G and V

๏ Isolated directly from penicillium molds; fermentation produces large yields

๏ Fairly narrow spectrum of coverage

๏ Highly susceptible to beta-lactamase and penicillinase (e.g. S. aureus) activity

Penicillin G(benzylpenicillin)

Penicillin VPenicillin VK, potassium salt(phenoxymethylpenicillin)

Semi-synthetic penicillins

๏ Cleave off natural sidechains with amidase to yield the 6-aminopenicillanic acid (6-APA) core, which can be synthetically substituted w/ other sidechains.

๏ Alter the spectrum, stability, bioavailability, resistance to penicillinases

๏ Examples: amino-penicillins (amox, amp), nafcillin, dicloxacillin, piperacillin

Penicillin G Penicillin V

6-APA

Rside chainaffects activity,

lactamase susceptibility, immunogenicity

Penicillins general features

๏ Still widely prescribed and effective for bacteria that are not resistant

๏ Amoxicillin still one of the most widely used antimicrobials (#5 drug overall)

๏ Very potent, bactericidal, if pathogen is sensitive, MIC~0.02µg/ml

๏ Especially for semi-synthetic derivatives in combination w/ beta-lactamase inhibitors, can get broad spectrum coverage

๏ Generally very safe (good selective toxicity); targets the cell wall, which is unique to bacteria

๏ Penicillin allergies:

๏ One of the highest reported causes of a drug allergy, however actual incidence is believe to be somewhat lower than the 10% reported

Penicillin allergy

๏ 10% of population claims to be allergic to penicillins

๏ Testing reveals that 1-3% in fact have IgE-mediated responses to the drugs (Simpson M.D., Alyson B., et al. Allergy and Asthma Proceedings. March - April 2009, Vol. 30, No. 2: 192-201)

๏ Older penicillin preparations <1970 included more contaminants that may have contributed frequency of allergic reaction. Newer preparations are more pure.

๏ Infections themselves, including some viral infections (EBV, HIV, coxsackie, HBV, etc), can have associated rashes.

๏ Thus, it may not necessarily be the case that every patient who presents with a rash close to penicillin administration necessarily has a penicillin allergy

๏ If a patient presents a rash, they are generally considered allergic

๏ Fortunately, skin tests are now commercially available again

Penicillin allergy

๏ The beta-lactam ring is unstable. It opens up when bound to the PBP active site. Normally this isomer covalently acylates an active site residue to irreversibly shut down the PBP activity

๏Most small, simple drugs such as penicillins do not themselves directly cause allergic reactions; instead they first form covalent adducts (hapten + carrier complexes) with host proteins

๏ These complexes present antigens that are recognized by IgE antibodies, leading to immune responses

Penicillin allergy

๏ But an opened ring may also form an adduct with other proteins

๏ “Major determinant” of penicillin allergy involves conjugates forming with lysine side chains of host proteins. Penicilloyl lysyl antigen. IgE mediated response to major antigen.

๏ “Minor determinants” include adducts formed with cysteine and carboxyl residues. IgE mediated response directed against “minor determinants”

๏ Major vs minor only refer to the amounts of material observed, not to the immunological response

Penicilloyl determinant(major)

(minor)

(minor)

Penicillin allergy: major determinant

21

e) allergy

This is considered the "major determinant" of penicillin allergy. The "minor determinants"

are a variety of other penicillin breakdown products.

1) immediate - urticaria, pruritus, shock; occurs within 60 min – rare but highly feared; 1gE mediated and directed against minor determinants

2) accelerated - rash; occurs within 72 h - common (5-10% of treated); 1g M and 1g E directed against major determinant

3) late - fever, urticaria; occurs > 72 h – rare; 1g M and 1g E

4) incidence - 5% show (+) reaction with skin test using penicilloyl polylysine (Prepen #) 50-70% of (+) have clinical Sx on amin. of penicillins - mostly rash <1% of (+) have serious reaction; overall incidence is about <.02%, <.0014% ! death semisynthetic show $ reactions; oral show $ reactions relative to parenteral doses

but an allergy to one penicillin means that the patient would be assumed to have a problem with any penicillin

allergy to penicillin does not necessarily mean allergy to cephalosporins but cross reactivity does occur (~10%); rule: if patient has serious reaction to a penicillin, don't give any beta lactam except aztreonam

ampicillin ! 9.5% allergy; this is due, in part, to the chemical nature of ampicillin, i.e. not all ampicillin induced rashes are true penicillin allergies. Amoxicillin has a somewhat lower incidence

densensitization protocols can be employed if infection requires penicillin therapy for an allergic patient

a rare interstitial nephritis is sometimes seen which may be a type of allergic reaction

Penicilloyl determinant(major)

๏ Small fraction of penicillin is isomerized to penicillenic acid, which reacts with the terminal amino group on lysine side chains, yielding the penicilloyl lysyl major determinant

๏ 90% of modified proteins are of this variety

๏ Response occurs within 72h.

๏ Urticaria (hives), rash, pruritus (itch)

๏ If a patient presents a rash, they are considered allergic

Penicillin allergy: major determinant

๏ Small fraction of penicillin is isomerized to penicillenic acid, which reacts with the terminal amino group on lysine side chains, yielding the penicilloyl lysyl major determinant

๏ 90% of modified proteins are of this variety

๏ Response occurs within 72h.

๏ Urticaria (hives), rash, pruritus (itch)

๏ If a patient presents a rash, they are considered allergic

Penicillin allergy: minor determinant

๏ “Minor determinants”: Result from reaction of other breakdown products with cysteine residues on proteins to form penicillenyl and penicillamine conjugates

๏ These determinants are associated with serious reactions such as anaphylaxis, shock

๏ Usually appear within 1h of administration; immediate hypersensitivity (IgE)

๏ Anaphylaxis in1:5,000-10,000 treatments (0.01-0.02%)

๏ ~0.0015% fatal outcome

Penicilloyl determinant(major)

(minor)

(minor)

Penicillin allergy: testing๏ What is available?

๏ PrePen (AllerQuest); back on the market as of May, 2010

๏ Skin test (puncture or intradermal) containing the benzylpenicilloyl major determinant on a polylysine carrier; those who show a positive test (wheal and flare on skin) to PrePen have IgE against the major determinant and are classified as penicillin allergic

๏ PrePen does not include the minor determinant. Fresh, diluted PenG may be added to for the minor determinant.

PRE-PEN®benzylpenicilloyl polylysine injection, solution

Skin Test Antigen

DESCRIPTION:PRE-PEN® (benzylpenicilloyl polylysine injection USP) is a sterile solution ofbenzylpenicilloyl polylysine in a concentration of 6.0 X 10-5 M (benzylpenicilloyl)in 0.01 M phosphate buffer and 0.15 M sodium chloride. The benzylpenicilloylpolylysine in PRE-PEN is a derivative of poly-l-lysine, where the epsilonamino groups are substituted with benzylpenicilloyl groups (50-70%) formingbenzylpenicilloyl alpha amide. Each single dose ampule contains 0.25 mLof PRE-PEN.

PRE-PEN has the following structure:

CLINICAL PHARMACOLOGY:PRE-PEN is a skin test antigen reagent that reacts specifically with ben-zylpenicilloyl IgE antibodies initiating the release of chemical mediatorswhich produce an immediate wheal and flare reaction at a skin test site. Allindividuals exhibiting a positive skin test to PRE-PEN possess IgE againstthe benzylpenicilloyl structural group which is a hapten. A hapten is a lowmolecular weight chemical that conjugates with a carrier (e.g. poly-l-lysine)resulting in the formation of an antigen with the hapten’s specificity. Thebenzylpenicilloyl hapten is the major antigenic determinant in penicillin-allergic individuals. However, many individuals reacting positively to PRE-PENwill not develop a systemic allergic reaction on subsequent exposure totherapeutic penicillin, especially among those who have not reacted topenicillins in the past. Thus, the PRE-PEN skin test determines the presenceof penicilloyl IgE antibodies which are necessary but not sufficient for acuteallergic reactions due to the major penicilloyl determinant.

Non-benzylpenicilloyl haptens are designated as minor determinants, sincethey less frequently elicit an immune response in penicillin treated individuals.The minor determinants may nevertheless be associated with significantclinical hypersensitivity. PRE-PEN does not react with IgE antibodies directedagainst non-benzylpenicilloyl haptens.

INDICATIONS AND USAGE:PRE-PEN is indicated for the assessment of sensitization to penicillin(benzylpenicillin or penicillin G) in patients suspected to have clinicalpenicillin hypersensitivity. A negative skin test to PRE-PEN is associatedwith an incidence of immediate allergic reactions of less than 5% after theadministration of therapeutic penicillin, whereas the incidence may be morethan 50% in a history-positive patient with a positive skin test to PRE-PEN.These allergic reactions are predominantly dermatologic. Whether a negativeskin test to PRE-PEN predicts a lower risk of anaphylaxis is not established.Similarly, when deciding the risk of proposed penicillin treatment, there arenot enough data at present to permit relative weighing in individual casesof a history of clinical penicillin hypersensitivity as compared to positive skintests to PRE-PEN and/or minor penicillin determinants.

CONTRAINDICATIONS:PRE-PEN is contraindicated in those patients who have exhibited either asystemic or marked local reaction to its previous administration. Patientsknown to be extremely hypersensitive to penicillin should not be skin tested.

WARNINGS:The risk of sensitization to repeated skin testing with PRE-PEN is notestablished. Rarely, a systemic allergic reaction including anaphylaxis(see below) may follow a skin test with PRE-PEN. To decrease the risk ofa systemic allergic reaction, puncture skin testing should be performedfirst. Intradermal skin testing should be performed only if the puncturetest is entirely negative.

PRECAUTIONS:General:No reagent, test, or combination of tests will completely assure that areaction to penicillin therapy will not occur.

The value of the PRE-PEN skin test alone as a means of assessing the risk ofadministering therapeutic penicillin (when penicillin is the preferred drug ofchoice) in the following situations is not established:

1. Adult patients who give no history of clinical penicillin hypersensitivity.2. Pediatric patients.

In addition, the clinical value of PRE-PEN where exposure to penicillin issuspected as a cause of a current drug reaction or in patients who areundergoing routine allergy evaluation is not known. Likewise, the clinical valueof PRE-PEN skin tests alone in determining the risk of administering semi-synthetic penicillins (phenoxymethyl penicillin, ampicillin, carbenicillin,dicloxacillin, methicillin, nafcillin, oxacillin, amoxicillin), cephalosporin-derived antibiotics, and penem antibiotics is not known.

In addition to the results of the PRE-PEN skin test, the decision to administeror not administer penicillin should take into account individual patient factors.Healthcare professionals should keep in mind the following:

1. A serious allergic reaction to therapeutic penicillin may occur in apatient with a negative skin test to PRE-PEN.

2. It is possible for a patient to have an anaphylactic reaction to ther-apeutic penicillin in the presence of a negative PRE-PEN skin test anda negative history of clinical penicillin hypersensitivity.

3. If penicillin is the drug of choice for a life-threatening infection,successful desensitization with therapeutic penicillin may be possibleirrespective of a positive skin test and/or a positive history of clinicalpenicillin hypersensitivity.

Pregnancy – Pregnancy Category C:Animal reproduction studies have not been conducted with PRE-PEN. It isnot known whether PRE-PEN can cause fetal harm when administered to apregnant woman or can affect reproduction capacity. The hazards of skintesting in such patients should be weighed against the hazard of penicillintherapy without skin testing.

ADVERSE REACTIONS:Occasionally, patients may develop an intense local inflammatory responseat the skin test site. Rarely, patients will develop a systemic allergic reaction,manifested by generalized erythema, pruritus, angioedema, urticaria,dyspnea, hypotension, and anaphylaxis. The usual methods of treating askin test antigen-induced reaction — the applications of a venous occlusiontourniquet proximal to the skin test site and administration of epinephrineare recommended. The patient should be kept under observation forseveral hours.

DOSAGE AND ADMINISTRATION:SKIN TESTING DOSAGE AND TECHNIQUESkin testing responses can be attenuated by interfering drugs (e.g. H1-antihistamines and vasopressors). Skin testing should be delayed until theeffects of such drugs have dissipated, or a separate skin test with histaminecan be used to evaluate persistent antihistaminic effects in vivo. Due to therisk of potential systemic allergic reactions, skin testing should be performedin an appropriate healthcare setting under direct medical supervision.

Puncture Testing:Skin testing is usually performed on the inner volar aspect of the forearm. Theskin test antigen should always be applied first by the puncture technique.After preparing the skin surface, apply a small drop of PRE-PEN solutionusing a sterile 22-28 gauge needle. The same needle can then be used tomake a single shallow puncture of the epidermis through the drop ofPRE-PEN. Very little pressure is required to break the epidermal continuity.Observe for the appearance of a wheal, erythema, and the occurrence ofitching at the test site during the succeeding 15 minutes at which time thesolution over the puncture site is wiped off. A positive reaction consists ofthe development within 10 minutes of a pale wheal, sometimes withpseudopods, surrounding the puncture site and varying in diameter from 5to 15 mm (or more). This wheal may be surrounded by a variable diameterof erythema, and accompanied by a variable degree of itching. The mostsensitive individuals develop itching quickly, and the wheal and erythema areprompt in their appearance. As soon as a positive response as definedabove is clearly evident, the solution over the scratch should be immediatelywiped off. If the puncture test is either negative or equivocally positive (lessthan 5 mm wheal with little or no erythema and no itching), an intradermaltest may be performed.

NHR

CH

NH

H

H

R = Benzylpenicilloyl or H

n > 40

H

S

COCO COOHN C

CH

NHNHNH CH CH CHCO CO COO

]2

C CCH2 CH( )3 2

4

NHR

CH ][[ 24

NHR

CH ][ 24

3+

๏ A patient may only exhibit an IgE-mediated response to the minor determinant

๏ Ideally a penicillin allergy test would include both major and minor determinants

Penicillin allergy๏ For patients who have a positive skin test (PrePen+PenG), 40-70% may exhibit an

anaphylactic reaction if penicillin were to be administered

๏ For patients who have a negative skin test, 1-3% may exhibit a reaction (usually mild) when penicillin is administered

๏ If minor determinants are not included (i.e. PenG), 3-10% of allergic patients may be missed by Pre-Pen

๏ Desensitization. If penicillin or beta-lactam is absolutely needed for patient with penicillin allergy, desensitization protocols are available (e.g. oral desensitization with PenV). Must be carefully monitored.

๏ Examples where this might be indicated:

๏ Strep. pyogenes is still sensitive to penicillins, and they are potent

๏ Syphilis (caused by the spirochete Treponema pallidum) in pregnant women.

http://www.cdc.gov/std/treatment/2006/penicillin-allergy.htm

Penicillin allergy cross-reactivity

๏ Cross-reactivity with other beta-lactams:

๏ If a patient has had a serious reaction (e.g. anaphylaxis), do not give other beta-lactams, except aztreonam (monobactam), which has no cross-reactivity

๏ Allergy to penicillins does not necessarily correlate with allergy to cephalosporins, but 10% does occur; if a patient has a rash w/ penicillin, may switch to a cephalosporin

๏ If a patient has shown an allergy to a cephalosporin, they are presumed to be allergic to penicillins as well

๏ Oral administration gives fewer reactions than IV or IM, probably due to more gradual exposure of immune system to the drug

๏ In general, the semi-synthetic penicillins show fewer allergic reactions

๏ Ampicillin also has a separate rash associated with it; affects 9.5% of patients. Generally more allergenic than PenG or V

Comparative features of penicillins

๏ Stability of penicillins in stomach acid variable๏ PenG is destroyed by acid, PenV more stable

๏ Newer derivatives such as amoxicillin have much better stability and bioavailability

๏ Susceptibility Gram+ penicillinases (narrow spectrum beta-lactamase) significant for PenG, PenV, amoxicillin, ampicillin๏ Dicloxacillin considered a “penicillinase resistant” penicillin

๏Highly susceptibility to Gram- beta-lactamases; combine with beta-lactamase inhibitors to get coverage of Gram- bugs

RR-group side chain

affects spectrum, activity, beta-lactamase susceptibility,

immunogenicity

drug oral absorptionPenG 15-30%PenV 60%

Ampicillin 30-50%Amoxicillin 70-80%

General features of penicillins

๏Not significantly metabolized. Significant amounts are excreted in unmodified, active form in urine. PenG ~80% excreted within 3-4h.๏ Can be effective therapeutic for urinary tract infections (UTI)

๏ Frequent dosing required

๏ Co-administered with probenicid to inhibit renal excretion. Increases plasma concentrations of penicillins and cephalosporins ~2x.

๏ Low penetration to cerebrospinal fluid unless inflammation is present

Properties of Penicillins

23

TABLE 1 - Properties of Penicillins

Type of penicillin Structure (R group) Oral

absorption

Routes of

admin.

1. "Natural:

Penicillin G

Penicillin V

poor

60-70%

IV, IM

PO

2. Amino

Ampicillin

Amoxicillin

30-50%

70-90%

PO, IV, IM

PO

3. Penicillinase resistant

Nafcillin

Oxacillin

Dicloxacillin

poor

poor

good

IV, IM

IV, IM

PO

4. Extended spectrum

Carbenicillin (indanyl)

Ticarcillin

Piperacillin

OK

poor

poor

PO

IV, IM

IV, IM

type of penicillin R group structure oral absorption route of administration

๏ Amino penicillins, more polar, better Gram- porin penetration

RR-group side chainaffects spectrum, activity,

beta-lactamase susceptibility, immunogenicity

Penicillinase-resistant penicillins:“anti-Staph” (MSSA) penicillins

23

TABLE 1 - Properties of Penicillins

Type of penicillin Structure (R group) Oral

absorption

Routes of

admin.

1. "Natural:

Penicillin G

Penicillin V

poor

60-70%

IV, IM

PO

2. Amino

Ampicillin

Amoxicillin

30-50%

70-90%

PO, IV, IM

PO

3. Penicillinase resistant

Nafcillin

Oxacillin

Dicloxacillin

poor

poor

good

IV, IM

IV, IM

PO

4. Extended spectrum

Carbenicillin (indanyl)

Ticarcillin

Piperacillin

OK

poor

poor

PO

IV, IM

IV, IM

type of penicillin R group structure oral absorption route of administration

๏ Bulky side chains reduce binding of resistant penicillins to the penicillinase

๏ Methicillin was of this class, but no longer in use

Extended spectrum penicillins:“anti-Pseudomonas” penicillins

23

TABLE 1 - Properties of Penicillins

Type of penicillin Structure (R group) Oral

absorption

Routes of

admin.

1. "Natural:

Penicillin G

Penicillin V

poor

60-70%

IV, IM

PO

2. Amino

Ampicillin

Amoxicillin

30-50%

70-90%

PO, IV, IM

PO

3. Penicillinase resistant

Nafcillin

Oxacillin

Dicloxacillin

poor

poor

good

IV, IM

IV, IM

PO

4. Extended spectrum

Carbenicillin (indanyl)

Ticarcillin

Piperacillin

OK

poor

poor

PO

IV, IM

IV, IM

type of penicillin R group structure oral absorption route of administration

๏ Charged, polar R-group improved permeability through Gm- porins

๏ Improved binding to PBP3 in Pseudomonas

๏ Used synergistically with aminoglycosides

Antimicrobial spectrum of penicillins

penicillin type Staph penicillinase resistance?

Gram- beta-lactamase

resistance?useful coverage route of

administration

Penicillin G no noGram+; S. pyogenes,some neisseria (Gm-) IV

Penicillin V no no Gram+; some neisseria PO

Ampicillin(aminopenicillin) no no Gram+; some Gram- due

to better porin penetration IV, IM

Amoxicillin(aminopenicillin) no no Gram+; some Gram- due

to better porin penetration PO

Nafcillin(penicillinase-

resistant)yes no Staph (not MRSA) IV, IM

Oxacillin(penicillinase-

resistant)yes no Staph (not MRSA) IV, IM

Dicloxacillin(penicillinase-

resistant)yes no Staph (not MRSA) PO

Antimicrobial spectrum of penicillins

penicillin type Staph penicillinase resistance?

Gram- beta-lactamase

resistance?useful coverage route of

administration

Piperacillin(extended spectrum) no

bit better than ticarcillin; usually combined w/ a

lactamase inhibitor e.g. tazobactam

Gram+anaerobes

*PseudomonasEnterobacteriaciae

{Enterobacter,E.Coli,

Klebsiella,Serratia,

Salmonella,Shigella,

Providencia,Citrobacter,

Proteus}

IV, IM

Ticarcillin(extended spectrum) no

no; usually combined w/ a

lactamase inhibitor, e.g. clavulanic acid

similar to pip. IV, IM

Beta-lactamase inhibitors

๏ Used to overcome beta-lactamase-related resistance to beta-lactams; not effective against all beta-lactamases, however

๏ Bind to beta-lactamase active site and irreversibly inactivate them by forming a covalent linkage to the active site serine

๏ Minimal antibiotic activity by themselves๏ Combination therapy with beta-lactam antibiotics๏ Example: Augmentin (amoxicillin + clavulanic acid)

clavulanic acid sulbactam tazobactam

Penicillins combined with beta-lactamase inhibitors

penicillin typeStaph beta-lactamase

(penicillinase) resistance?

Gram- beta-lactamase

resistance?useful coverage route of

administration

Amoxicillin+

clavulanate(Augmentin ®)

yes yes broad PO

Ampicillin+

sulbactam(Unisyn ®)

yes yes broad IM, IV

Ticarcillin+

clavulanate(Timentin ®)

yes yes broad IV, IM

Piperacillin+

tazobactam(Zosyn ®)

yes yes broad IV, IM

Penicillins combined with beta-lactamase inhibitors

๏Generally would like to use as narrow spectrum of antibiotic as possible so as to reduce impact on non-pathogenic flora and so as to maintain balance, prevent overgrowth (e.g. C. difficile, Candida yeast)

๏ But often we do not know the bacterial target, or may have a super-infection involving multiple species