Beta Lactams and Aminoglycosides

Question 1

what is the mechanism of action for penicillins

Answer 1

inhibition of cell wall synthesis

Question 2

what are three main adverse effects of penicillins

Answer 2

1) hypersensitivity (incl. contact hypersensitivity, not used topically)

2) potentially fatal colitis in hindgut fermenters with oral administration

3) reduction of seizure threshold (Beta lactams inhibit GABAa receptors in the brain)

Question 3

what spectrum does penicillin G cover

Answer 3

Gram +ve aerobes, anaerobes

Question 4

what spectrum does amoxicillin cover

Answer 4

Gram +ve aerobes, anaerobes, several Gram -ve aerobes

Question 5

what pencillin drugs are first line vs second line

Answer 5

first line = penicillin G, amoxicillin
second line = potentiated penicillins

Question 6

what are the PK features of penicillin (3)

Answer 6

-excreted intact in the urine
-penicillin G is not acid stable
-oral bioavailability of amoxicillin is 90%

Question 7

mechanism of action of cephalosporins

Answer 7

inhibition of cell wall synthesis

Question 8

main adverse effects of cephalosporins (3)

Answer 8

-hypersensitivity
-oral administration may cause potentially fatal colitis in hindgut fermenters
-reduction in seizure threshold

Question 9

what spectrum does first generation cephalosporins cover

Answer 9

gram +ve aeroves, anaerobes, some gram -ve aerobes

Question 10

what spectrum does third generation cephalosporins cover

Answer 10

mainly gram -ve aerobes

Question 11

what cephalosporins drugs are first line vs second line

Answer 11

first line = first generation
second line = third generation

Question 12

PK features of cephalosporins (3)

Answer 12

-only a few are acid stable (eg cephalexin)
-not destroyed by penicillinases, but may be inactivated by some beta lactamases
-some third generation drugs enter CNS readily

Question 13

mechanism of action for aminoglycosides

Answer 13

inhibition of protein synthesis (bactericidal effect)

Question 14

main adverse effects of aminoglycosides (2)

Answer 14

-nephrotoxicity
-ototoxicity

Question 15

general spectrum of aminoglycosides

Answer 15

gram -ve aerobes, staph, mycoplasma

Question 16

first line vs second line for aminoglycosides

Answer 16

first = topical administration
second = systemic administration

Question 17

PK features of aminoglycosides (2)

Answer 17

-highly ionized (negligable oral or topical administration)
-food residues > 1 year with parenteral administration

Question 18

what is the most commonly used AMD?

Answer 18

penicillins

Question 19

what can destroy the BL ring in penicillins?

Answer 19

warming or freezing temperatures

Question 19

how is pencillin half life increased?

Answer 19

depot formulations…. pencillin bound to procaine or benzathine, where penicillin slowly dissociates from it at the IM/SQ injection site

Question 19

penicillins are only effective against _____ bacteria

Answer 19

growing

Question 20

why do pencillins work best on gram positive bacteria

Answer 20

because they have a thick unprotected peptidoglycan layer

Question 21

what bacteria is resistant to penicillin drugs

Answer 21

-poor penetration of outer lipid bilayer in gram negative bacteria

-acquired bacterial penicillinases (plasmid encoded, can be transfered from other bacteria)

Question 22

is penicillin narrow or broad spectrum?

Answer 22

narrow

Question 23

what is an example of an extended spectrum pencillin?

Answer 23

amoxicillin

Question 24

what does amoxicillin cover

Answer 24

gram positive aerobes, anaerobes, and SOME gram negative aerobes (many enterobacteriaceae)

Question 25

how can bacterial penicillinases be inactivated ? example of a drug

Answer 25

with penicillinase inhibitors such as clavulanic acid clavamox! amoxicillin+clavulanic acid formulation

Question 26

how to tell if a drug is a cephalosporin name wise

Answer 26

starts with ceph or cef

Question 27

what are third generation cephalosporins mainly effective against

Answer 27

gram negative aerobes

Question 28

how well do third generation cephalosporins enter the CNS

Answer 28

reasonably well

Question 29

are cephalosporins effective if administered orally

Answer 29

no.... most are not acid stable

Question 30

what is an example of a first generation cephalosporin? route of administration?

Answer 30

cephalexin, oral

Question 31

what do first generation cephalosporins cover

Answer 31

gram +ve aerobes, anaerobes, some gram -ve aerobes

Question 32

what are example of first generation cephalosporins that are administered parenternally

Answer 32

-cefazolin; used for surgical prophylaxis in small animals (injectable) -cephapirin; intramammary for cattle

Question 33

what are third generation cephalosporins mainly used against? what can they cover in addition to that?

Answer 33

mainly covers gram -ve aerobes covers some gram +ve aerobes, some anaerobes

Question 34

example of a third generation cephalosporin and what its used for

Answer 34

ceftiofur; resp infections in livestock, metritis and foot rot in cattle, UTI in dogs

Question 35

example of a third generation cephalosporin in small animals and duration

Answer 35

cefovecin/convenia; used for resp and skin infections in dogs/cats 2 week formulation essentially guarantees inappropriate duration of therapy in many patients

Question 36

two main clinical uses of aminoglycosides

Answer 36

1- systemic administration for dangerous gram -ve aerobic infections (septicemia) 2- topical (staph)

Question 37

do aminoglycosides cross membranes well

Answer 37

no, they are highly ionized which causes limited ability to cross membranes

Question 38

what route of administration is needed for systemic treatment with aminoglycosides

Answer 38

parenternally

Question 39

do aminoglycosides kill bacteria

Answer 39

yes!

Question 40

what is resistant to aminoglycosides

Answer 40

-anaerobes.... because entry of drug into the cell requires oxygen dependent transporter that is absent in anaerobes -plasma acquired aminoglycosidase

Question 41

what antibiotic should you never give a dehydrated patient or renal disease patient? why?

Answer 41

aminoglycosides! ordinary dose can be very damaging to kidneys of these patients

Question 42

how do you minimize damage to kidneys when giving aminoglycosides

Answer 42

by allowing a washout period... give single daily dose and allow concentrations to fall for remainder to the day

Question 43

can you use aminoglycosides in food animals

Answer 43

-you can.... but IM use in cattle may result in drug residues detectable for more than a year

Question 44

what do you need to ensure before using topical otic aminoglycoside

Answer 44

ensure tympanum is intact... otherwise can cause permanent hearing loss

Question 45

what is the most commonly used AG? spectrum?

Answer 45

gentamicin broad spectrum

Question 46

when is tobramycin used

Answer 46

used second line for infections resistant to gentamicin

Question 47

when is amikacin used

Answer 47

used second line for infections resistant to gentamicin resistant to many aminoglycosides