antimicrobial therapy Flashcards

1
Q

Anti“biotic”

A

-substance produced by
bacteria, and active against other bacteria

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2
Q

Anti“microbial”

A

-substance (either naturally produced or synthetic) that is active against
microbes, including bacteria, fungi, protozoa

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3
Q

infection site in antimicrobial therapy ex abscess

A

-depending on where the infection is we have to choose an antibiotic which will get to the site of the infection
-ex> abscess are walled off and hard to get antimicrobials into.
-not likely to be effective are aminoglycosides, B lactams, trimeth/ sulfa.

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4
Q

things to think about when choosing an antimicrobial therapy

A
  • Where is the infection located?
  • Will the antimicrobial distribute to the infection site?
    -what are the AE of the drug?
    -What is the appropriate drug
    formulation and dosage regimen?
    -Will the antimicrobial be effective in the pathogen’s environment?
    -For food animals can you stay
    “on label”?
    -cost
    -parmacodynamics and pharmacokinetis
    -risk
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5
Q

goal of antimicrobial therapy

A

-sufficiently suppress the bacteria and infection so that they can be eliminated by the host’s immune system?
-don’t need to kill all bacteria most of the time.
-just want enough drug so that the infection stops proliferating.

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6
Q

high plasma [ ] in blood

A

-High plasma drug concentrations are
assumed to be advantageous.
-higher in blood means higher everywhere else
-not always true
-for soft tissue infections (wounds, pyoderma) most bacteria are located ESF so works in equilibrium with plasma so good indicator.
- Exceptions exist: new macrolide drugs
have very low plasma concentrations but
extremely high tissue concentrations: Bind to leukocytes, carried to site of infection (lungs)

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7
Q

MIC

A

-Minimum Inhibitory Concentration (MIC)
 lowest drug concentration that inhibits bacterial growth
 Dose to reach target [plasma] of 2-10x the MIC
-determined by microdilution, disk diffusion (qualitative), E-tests.

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8
Q

Minimum Bactericidal Concentration (MBC)

A

 lowest drug concentration to kill 99.9% of the bacteria

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9
Q

Mutant Prevention Concentration (MPC)

A

 MIC of the least-susceptible (i.e. more resistant) single-
step mutant bacterial population

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10
Q

susceptibility testing

A

-helps guide theraputic decisions. does not gaurantee drug success OR failure.
-predictions can be WRONG: does not account for:
-host immune system, drug distribution, drug efficacy in plasma/ tissues, bacterial growth rate, mixed infections.

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11
Q

Susceptibility Testing Limitations

A
  • Assumes drug concentrations are only reached via
    SYSTEMIC administration
  • LOCAL administration may reach much higher concentrations
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12
Q

Genomics

A
  • Identify key genetic determinants of resistance (e.g., mecA, ampC genes)
  • Future diagnostic approach for fast, accurate, and cheap
    antimicrobial susceptibility testing?
    -uses whole genome sequenxing and metagenomics for AMR detection.
    -theres a large disconnet between our understanding of AMR genotype and phenotype.
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13
Q

Bactericidal

A

 Ratio of MBC to MIC is < 4-6
 i.e., it’s possible to obtain concentrations in the patient that will kill 99.9% of the bacteria
-Categories are NOT absolute!
Do NOT choose therapy based on cidal vs static!
-ex floroquinolines

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14
Q

Bacteriostatic

A

 Ratio of MBC to MIC is large
 i.e., it’s not safe or feasible to administer enough antimicrobial
to kill 99.9% of the bacteria
Categories are NOT absolute!
Do NOT choose therapy based on cidal vs static!
ex. tetracyclines

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15
Q

Post-Antibiotic Effect (PAE)

A

 Bacterial growth remains suppressed after the [antimicrobial] has dropped below MIC. still working even though drug isn’t there anymore.
 May be the reason that many dosage regimens are effective, despite not maintaining concentrations > MIC
 MAY allow for longer interval between doses
 PAE is dependent on the specific combo of antimicrobial & bacteria

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16
Q

PK-PD Integration for Antimicrobials concentration vs time dependent

A

 Bacterial kill-curve studies show that antimicrobials can be:
* Concentration dependent:
 AUC0-24 hr: MIC, the more drug and higher exposure you have the better.
 Cmax: MIC, bigger the exposure to MIC better it works.
* Time dependent  T > MIC, high exposure or concentration isn’t as important as time they spend above MIC of pathogen. And concentration can’t drop below MIC and stay below

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17
Q

approach for time vs concentration dependant therapy

A

-For concentration (i.e., dose)-dependent killers, more is better.
- For time-dependent killers, dosing more often is better.
 Same dose, but divided more times/day
 BUT: may be poor client compliance with frequent dose regimens
 Infrequent dosing requires “long-acting” form
 Slow absorbing (“flip-flop”) formulations
 e.g., long acting OTC, CCFA (Excede)
 High protein binding (cefovecin)

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18
Q

Beta lactams structure

A

-penicillin, cephalosporins
-B lactam ring: resistance mechanism breaks down the ring with beta-lactamase’s.

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19
Q

penicillins used in vet med

A
  • Crystalline penicillin G (Na+ or K+)
    – Sterile formulations for injection (human drugs) IV!
    – Soluble powder for drinking water (vet drugs non-sterile)
  • Procaine Penicillin GVM
    – “white” injectable penicillin (short acting daily injections or long acting in oil. IM or SC ONLY.
    – Oral feed premixes
  • Benzathine Penicillin GVM
    – “Long-acting” injectable penicillin (Duplocillin LA) IM or SC only
    -make sure always look at label as there are many different types of penicillin formulations.
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20
Q

penicillin G: mechanism of action

A

-Act by disrupting synthesis of bacterial cell wall:
* Inhibit the Penicillin-Binding Proteins (PBPs) found
on the outside of bacterial cell membrane
* This interferes with enzymes (transpeptidase) needed
for peptidoglycan synthesis (part of cell wall)
* Causes lysis of growing bacterial cells
– Bactericidal – but only if bacteria is actively growing

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21
Q

Penicillin G: Mechanism of Action in different bacteria types

A

– Gram (+)
* lots of peptidoglycan in cell wall
* High affinity of PBPs for β-lactams=works good on gram +
– Gram (–)
* Lesser peptidoglycan in cell wall
* Lower affinity of PBPs for β-lactams, doesn’t work as well on gram -, cant penetrate the cell wall.
-dosed in IU. 1 IU = 0.6 ug pen G

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22
Q

penicillin G resistance

A
  • some gram + (staph) have Penicillinase or β-lactamase enzymes so not susceptible to penicillin. (but can be susceptible to cephalosporins)
  • Inability of β-lactam to penetrate bacterial cell wall
    -gram -: no susceptible to penicillin: Can’t penetrate cell wall
    -gram -: not susetable to endogenous b-lactamase producer.
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23
Q

Penicillin G (Benzylpenicillin):
Spectrum of Activity

A

-Many Gram (+) (ex strep)
(but NOT most Staph,
which make β-lactamase)
-many anaerobes
Gram (+)
* Actinomyces species
* Trueperella pyogenes
* Some Bacillus anthracis,
Corynebacterium, Erysipelothrix
rhusiopathiae, and Listeria spp.
A few Gram (-)
* Some Histophilus & Pasteurella
Most anaerobes
* Fusobacterium, some Clostridium, some Bacteroides

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24
Q

Penicillin G (Benzylpenicillin): resistance bacteria

A

Most Gram (-)
* Produce β-lactamase
* Can’t penetrate cell wall
* Low affinity PBP
Most Staph spp.
* Produce β-lactamase

25
Penicillin PK
absorption (oral): * Poor oral absorption of penicillin G due to rapid hydrolysis in stomach acid – Exception: Phenoxymethyl penicillin (penicillin V)=acid stable -penicillin in oral feedmix or water, used locally in gut doesn't absorb to systemic. -distribution: weak acid so highly ionized at pH 7.4. low Vd, good plasma concentrations and ESF. more distribution to inflammatory tissues. -elimination: most in renal tubule. short T1/2 life except benz formulations. (flip flop kinetics)
26
penicillin PK absorption different formulations
Absorption (parenteral): * Crystalline (Na+ & K+) pen G: – Only dosage form that can be used IV – Rapid absorption after IM or SC injection * Procaine pen G: – Procaine salt more slowly absorbed from IM injection site than crystalline forms (especially with oil formulations) * Procaine causes vasoconstriction at injection site – Results in lower, but more sustained, plasma concentrations – Injections in neck absorbed more rapidly than in hindquarters * And less carcass damage! – NEVER USE FOR IV INJECTION (CNS signs) * Benzathine penicillin G: – Benzathine salt is poorly soluble, very slowly absorbed -released so slow doesnt reach MIC. high drug residues
27
penicillin = time dependent antimicrobial
* Efficacy isn’t based on reaching high Cmax * Need to Keep penicillin conc. > MIC for as long as possible (most of the dosing interval) – Crystalline penicillin: May require TID / QID dosing – Procaine Pen G: Once daily dosing – “LA” procaine/benzathine Pen G: Days between doses * Prolonged absorption (flip flop kinetics) * NOTE: only useful if plasma concentrations actually reach pathogen MIC!
28
Penicillin Adverse Reactions
-Hypersensitivity: Due to R1 side chain, not beta-lactam * Anaphylaxis / local inflammation (Type I) * Autoimmune hemolytic anemia (Type II) * Vasculitis (Type III) -GI flora changes (diarrhea) most common * Especially hindgut fermenters (horses, rodents, rabbits) -Drug residues in food animals (give in injection triangle)
29
isoxazolyl penicillins vs pen G
* Active against same bacteria as Pen G – But generally a bit less potent than Pen G ****Impervious to S. aureus penicillinase*** – so historically used for Staph infections * Cloxacillin– Dry-Clox intramammary suspension treats shaphylocoocus mastitis in vet med - Methicillin-resistant Staph aureus & pseudintermedius (MRSA, MRSP)
30
Methicillin-resistant Staph aureus & pseudintermedius (MRSA, MRSP)
: resistant due to different penicillin binding protein. mecA gene. has a LOW AFFINITY FOR ALL B-LACTAM DRUGS (resistant)
31
Antistaphylococcal Penicillins spectrum
-Many Gram (+) (including most Staph.) -anarobes Isoaxyzyl penicillins
32
Beta-lactam antimicrobials: Aminopenicillins
-spectrum: active agaisnt all bacteria that pen G is, but amino groups allow better penetration through the outer layer of gram-neg bacteria (esp. amoxicillin) -some gram neg, all gram pos (not staph), anaerobes -still susceptible to degradation by enzymes. forms: * Ampicillin * Amoxicillin:
33
Ampicillin
-Aminopenicillins – Trihydrate salt injectable suspension (PolyflexVM) * For IM/SC (not IV) use in cattle, swine, dogs, cats – Many human sterile crystalline Na+ (IV injection) and oral forms
34
Amoxicillin
-aminopenicillin – Many veterinary oral tablets / suspensions * With/without clavulanic acid * Indications: wide variety of infections in dogs/cats – Soluble powder for medicated water * Swine & poultry
35
aminopenicilin PK
Absorption: * Oral: Both ampicillin & amoxicillin are acid-stable * Ampicillin oral F is ~ ½ that of amoxicillin – Amoxicillin: both fed or fasting state is OK, good on stomach. * Injectable: – Ampicillin trihydrate – slowly absorbed (SC, IM) – Ampicillin sodium – rapid, can be given IV -short 1/2 life. BID dosing orally. 2 but 3 is better a day. SID for ampicillin trihydrate after IM -time dependent antimicrobials
36
aminopenicillins adervse effects
Adverse events: * Hypersensitivity (due to R1 side chain) – Slightly less than Pen G? – Cross-reactivity in patients with Pen G hypersensitivity? probably not seen due to different side chains. you will just switch to a non B-lactam * Oral adverse events (vomit, diarrhea)– Intestinal flora disruption:
37
Beta-lactam antimicrobials: Carboxypenicillins (anti-pseudomonal penicillins)
-piperacillin – All human formulations – Usually administered IV so only used in clinic in serios cases. * With β-lactamase inhibitor like tazobactam – Expensive
38
Anti-pseudomonal penicillins: Spectrum of Activity
Active against Gram (-) * Except β-lactamase producers Active against Pseudomonas * Can penetrate its cell wall - anaerobes BUT: ↓ activity against Gram (+) -only used in clinic
39
Beta-lactam antimicrobials: β-lactamase inhibitors
* Clavulanic acid – In many oral tablet and suspensions for small animals (Clavamox, Clavaseptin, Aventiclav) * Human formulations: Different ratio of Amox: Clav
40
β-lactamase inhibitors: Mechanism of Action
-by providing B-lactamase inhibitors with penicillins they will not be susceptible to B lactamase enzymes. so always the penicillin to bind to binding protein. -Irreversibly binds to & inactivates β- lactamase enzymes – Allows β-lactam antimicrobial included in the formulation to bind with PBP
41
β-lactamase inhibitors: Spectrum of Activity
When included with amoxicillin: * Most Gram (+) – Including most β-lactamase producing Staph (unless methicillin-resistant → altered PBP) * Many Gram (-) * Many anaerobes -can add and in the MIC will make resistant microbials turn to susceptible microbials
42
β-lactamase Inhibitors (with aminopenicillin) specutrum
-some gram - -gram + (except MR-staph) -anaerobes
43
β-lactamase inhibitors: PK
Almost the same as amoxicillin... * Quickly & extensively absorbed after oral administration * Renal excretion * T1/2 elim similar to amoxicillin Minimal Adverse Events * If ADE do occur, probaly due to aminopenicillin portion (not β-lactamase inhibitor)
44
Carbapenems (extended-spectrum penicillins)
* Imipenem Extremely wide spectrum of activity: * Gram (+) * Gram (-) * Anaerobes * Impervious to β-lactamase enzymes DRUG OF LAST RESORT IN HUMAN MEDICINE, so DONT USE
45
Beta-lactam antimicrobials: Cephalosporins
-same B-lactam ring -cephalexin (rilexine or cefaseptin tablets) -cetiofur (EXCEDE is crystalline free acid) -cefovecin (Convenia injectable solution) -cefpodoxime (Simplicef tablets) * Cephapirin * Cefazolin (human formulation sterile injectable) used perioperative, give before surgery or during
46
CEPHALEXIN
-cephlosporin * Now only oral tablets * Indicated for canine superficial pyoderma caused by susceptible strains of Staphylococcus pseudintermedius
47
Cephalosporins: Mechanism of Action
More β-lactam drugs: so same as penicillin! * Act by disrupting synthesis of bacterial cell wall * Inhibit the Penicillin-Binding Proteins * Interferes with cell wall peptidoglycan synthesis General advantages of cephalosporins: * Stable against (some) beta-lactamase enzymes * Good affinity for target proteins (PBPs) * Good ability to penetrate bacterial cell wall – Including Gram (-) abit more gram - coverage
48
emerging resistance to cephlasporins
* Different β-lactamase enzymes: – Extended-spectrum β-lactamase enzymes (ESBL) – AmpC cephalosporinases – Metallo- β-lactamase enzymes * Modify the PBPs (mecA gene, others) ****cant use for mrsa its all B-lactams * Reduce cellular concentrations: – ↓ bacterial cell wall permeability – Induction of efflux pumps
49
cephlasporin spectrum of activity
Gram (+) * Strep spp. * Staph. aureus, pseudintermedius * Many other Gram (+) some Gram (-) * Many enterbacteriaciae – E. coli, Salmonella, Klebsiella – Histophilus, Mannheimia, Pasteurella Most anaerobes
50
resistant to cephlosporins
Gram (+) * Meth-resistant Staph spp. – Altered PBP * Enterococcus – inherently resistant to cephalosporins Gram (-) * Many enteric pathogens with ESBL activity * Rhodococcus equi * Pseudomonas (except Gr. 6&7) * Mycobacteria Anaerobes: Bacteroides * except cefoxitin
51
Cephalosporins distributions
Oral absorption: generally good * SimplicefTM: Cefpodoxime proxetil → prodrug Parenteral absorption: Depends on the formulation * Cefazolin: Extremely rapid – Can go IV * Ceftiofur sodium (Excenel) – very rapid – Can go IV (but only labelled for IM/SC) * Ceftiofur HCl (Excenel RTU EZ) – slower * Ceftiofur crystalline free acid (Excede) – very slow (long-acting formulation)
52
Cephalosporins: PK
Distribution: Low Vd -Metabolism occurs for some cephalosporins: * Ceftiofur → desfuroylceftiofur (less active metabolite) * Cephapirin → deacetylated in the liver Renal elimination (most cephalosporins) * Glomerular filtration + Tubular secretion Short half-life (1 – 2 h) with exeptions
53
Cephalosporins: PK exceptions Protein-binding & T1/2 elim
Cefpodoxime & (especially) cefovecin: * Extremely highly protein bound (>95%) * Cefpodoxime T½ = 5-6 HOURS in dogs * Cefovecin T½ = 5.5 - 6.9 DAYS after SC administration in dogs and cats – ↓ clearance in kidney due to high protein binding – Result = one dose every 2 weeks Ceftiofur T1/2 elim varies by formulation: * Ceftiofur sodium (Excenel) = 2 – 3 h in cattle * Ceftiofur HCl (Excenel RTU) = 20 h in pigs * Ceftiofur crystalline free acid (Excede): – 40+ h in cattle – 50 h in pigs
54
cephalosporins adverse effects
Mostly the same as penicillins * Hypersensitivity: same as penicillin. ex. eruption of skin. -more reactivity between older amino and cephs. * GI upset – Vomit (esp. cephalexin), diarrhea – Loss of normal GI flora can lead to bacterial overgrowth * Coagulopathies / blood dyscrasias (also rare) but goes away when drug is stopped – Ceftiofur: thrombocytopenia – Cephalexin: IMT
55
Cephalosporins: Concerns about AMR
-problem with compounded versions and extralabel uses. – Can’t alter the dose, route, frequency, or duration – Can use in minor species – Can use for different indication * BUT: Cannot use for prevention -some extralabel uses are prohibited: ovo chick injections, bio bullets in cattle (banned USA)
56
cephalosporins are inherently ineffective against which UTI pathogen?
enterococcus
57
Emergence of Vancomycin-Resistant Enterococci (VRE)
-Enterococcus: Inherent resistance to cephalosporins * Risk factors for VRE colonization and infection include prolonged hospital stays, exposure to intensive care units, transplants, hematologic malignancies, and exposure to antibiotics. – Exposure to cephalosporins is particularly important -if treated with cephosporin people are 3x more likey to get a Vancomycin-Resistant Enterococci infection.
58
Cetiofur
Cephalosporin type drug Excede crystalline Exenel in salt form
59
Cefovectin
Convenia Cephalosporin