Antibiotics

Question 1

What are the 9 major antibiotic categories?

Answer 1

• beta-lactams?
• macrolides and clindamycin
• tetracyclines/glycylcyclines
• glycopeptides
• aminoglycosides
• quinolones
• sulfonamides and trimethoprim
• metronidazole
• linezolid

Question 2

What is the mechanism of action of penicillins?

Answer 2

penicillins bind to penicillin-binding protein on the pathogen and inhibit peptidoglycan synthesis. Breaks the cell wall and prevents its production and repair

Question 3

Are penicillins bactericidal or bacteriostatic

Answer 3

bactericidal

Question 4

What forms of resistance have organisms developed against penicillins

Answer 4

• production of beta-lactamases – break the ring before it can bind
• lack of or altered PBPs
• efflux of drug out of cell
• failure to synthesize peptidoglycans such as mycoplasma or metabolically inactive bacteria

Question 5

What id the parenteral form of natural penicillin

Answer 5

Penicillin G

Question 6

what types of bacteria is penicillin G active against

Answer 6

gram positive bacteria and spirochetes (syphilis)

Question 7

Why can’t penicillin G be used orally?

Answer 7

highly acid labile and would be destroyed by stomach acid before it could absorb

Question 8

What forms of Pen G are available

Answer 8

• procaine pen G
• benzathine pen G (IM injection only)

Question 9

What is penicillin V

Answer 9

the oral formulation of penicillin G. It is more acid stable but must be taken on an empty stomach

Question 10

What kinds of infections are pen G and V used for

Answer 10

• Drug of choice for streptococci, pneumococci, meningococci, spirochetes, clostridia, anaeobic gp rods, and actinomyces
• also effective against enterococci which are very hard to kill

Question 11

what kind of penicillins are methicillin/cloxacillin?

Answer 11

isoxazolyl penicillins

Question 12

What bacteria were methicillin/cloxacillin designed for?

Answer 12

Staphylococcus aureus –> gram positive

Question 13

What are the other drugs in the methicillin/cloxacillin family?

Answer 13

flucloxacillin and dicloxacillin

Question 14

Does methicillin have activity against all gram positive bacterias

Answer 14

No, the activity is specifically against staph aureus

Question 15

Can we use methicillin/cloxacillin for to treat MRSA?

Answer 15

No, MRSA is the only staph aureus infection that won’t be treated by these medications

Question 16

What are aminopenicillins active against?

Answer 16

both gram positive and gram negative organisms

Question 17

What are the two drugs in the aminopenicillin category and what are their forms?

Answer 17

1. Ampicillin: used IV, not taken orally because dosing would have to be frequent. More acid stable than natural pens but they have poor bioavailability
2. Amoxicillin: used orally, better absorption than ampicillin because more acid stable, also available combined with clavulanic acid to inhibit beta-lactamases

Question 18

Which bacterial infections do we use aminopenicillins for?

Answer 18

• streptococci
• enterococci
• neiserria
• non-beta lactamase producing H. influenzae
• E. coli
• p. mirabilis
• Salmonella

Question 19

Which drug is in the ureidopenicillin class?

Answer 19

piperacillin

Question 20

What kind of activity do ureidopenicillins possess?

Answer 20

They have increased activity against gram negative rods, specifically Pseudomonas aeruginosa, which is very pathogenic

Question 21

How can piperacillin be administrated?

Answer 21

Parenteral (IV) only

Question 22

In what situations are ureidopenicillins (piperacillin) used?

Answer 22

only used in hospital, reserved for very sick patients and not seen in community pharmacy

Question 23

What beta lactamase inhibitor can be combined with piperacillin

Answer 23

tazobactam

Question 24

Describe the pharmacokinetics of all penicillins

Answer 24

• oral bioavailabilities varies across classes
• distributed widely to the tissues and to the CNS
• most penicillins are excreted by the kidney

Question 25

What is specific about amoxicillin and administration compared to other penicillins

Answer 25

amoxicillin is the only penicillin taken with food

Question 26

What are the half-lives of penicillins?

Answer 26

• short
• penicillin dosing is frequent
• cloxacillin is QID, the rest are mostly TID

Question 27

Are penicillins concentration dependent or independent, and what does this mean

Answer 27

Concentration independent:
- once a certain threshold of blood levels is reached, there is no more added killing potential
- goal of therapy is to keep the blood levels above the threshold for the whole duration of therapy
- most easily done with an IV drip, which is unrealistic and inconvenient

Question 28

What is a drug interaction with penicillins

Answer 28

oral contraceptives:
penicillins destruct the estrogens and prevent the enterohepatic recirculation

Question 29

What are the adverse effects of penicillins

Answer 29

• allergic reactions – anaphylaxis if severe
• serum sickness
• skin rash
• fever, nephritic, eosinophilia
• seizures, encephalopathy, delirium
• electrolyte imbalances
• neutropenia, thrombocytopenia
• diarrhea, gi upset (most common)

Question 30

Does the mechanism of action of cephalosporins differ from that of penicillins?

Answer 30

No, MOA of cephalosporins is the same. beta lactam ring binds to PBR on the pathogen and breaks the cell wall