Chapter 88: Drugs that weaken the Bacterial Cell Wall I: Penicillins

Question 1

Penicillins (PCN)

Answer 1

active against a variety of bacteria
Direct toxicity: low

Question 2

Penicillins (PCN) priniciple adverse effect

Answer 2

allergic reaction

Question 3

Penicillin (PCN) Structure

Answer 3

includes a beta lactam ring (betalactamase and penicillinase cause this to be destroyed)
disrupts cell wall
beta-lactam family: includes cephalosporins, aztreonam, carbapenems (imipenem, meropenem, and ertapenem)

Question 4

Penicillin (PCN) metabolism

Answer 4

minimal, excreted by kidneys (decreased dose for impaired kidney function)
toxicity can occur in renal impairment
possible neurotoxicity with toxic levels
slowing the infusing rate can buffer impact on kidneys

Question 5

Penicillin MOA

Answer 5

weakens the cell wall, causing bacteria to take up excessive water and rupture (cell lysis and death)
active only against bacteria undergoing growth and division
disrupts building cell wall and activates “auto-destruct)
bacteriacidal or bacteriostatic - depending on the drug concentration

Question 6

Penicillin mechanisms of bacterial resistance

Answer 6

inability of penecillins to reach their target (gram positive and gram negative)
production of altered (penicillin binding proteins) PBPs –> PCN can’t bind to them for antibacterial effect
inactivation of penicillins by bacterial enzymes - penicillinases (beta lactamases –> destroys beta lactam ring)

Question 7

Penicillin G: Prototype

Answer 7

has a narrow antibacterial spectrum and is unstable in stomach acid (only given PO if patient has GI infection)

Question 8

Penicillin G Protoype: forms

Answer 8

Rapid aborption: penicillin G potassium (IV) and penicillin G sodium (IV)
Long acting; absorbs slowly: procaine penicillin (IM), benzathine penicillin (IM)

Question 9

Penicillin G therapeutic uses

Answer 9

sextually transmitted diseases (STDs), streptococcus infections and certain anaerobes
drug of choice for syphillis and strep infection

Question 10

Penicillin G adverse effects

Answer 10

allergy - penicillins are the most common cause of drug allergy
pain at the injection site
phlebitis (if see strike of red vein, TAKE IV OUT, pH 2.8-4.5)

Question 11

Penicillin G Interactions

Answer 11

• aminoglycosides - potentiative; PCN weakens cell wall so aminoglycoside can get into cell easier—- can be used to augment action —-cannot be mixed together outiside the body—–Seperate administration - never in same IV solution (crystaluria)
• Oral contraceptive (use different method of birth control for at least 1 month after taking the antibiotic)
• Probenecid (used to prevent renal excretion so levels may remain elevated —- delays excretion; prolongs antibacterial effects —- not used much anymore; also risky for patients with renal issues)
• Bacteriostatic antibiotics (antagonistic; limit active growth; PCN works on growing cells)

Question 12

Types of penicillin allergy

Answer 12

immediate (2-3 min)
accelerated (1-72 hours)
late (days or weeks)

Question 13

Penicillin allergy Analphylaxsis

Answer 13

laryngeal edema
bronchoconstriction
severe hypotension

Question 14

Penicillin allergy treatment

Answer 14

epinephrine (1:1000 if anaphylactic and 1:10000 if coding or in cardiac arrest) 0.3mL
respiratory support
prevention - skin testing

Question 15

Development of penicillin allergy

Answer 15

first time use can happen
presence of penicillins in food supply, molds
prior use creates antibodies

Question 16

Management of patients with a history of penicillin allergy

Answer 16

avoid use unless potential benefit outweighs risk
assess for penicillin allergy in each patient who will be recieving penicillin
if history of mild reaction, consider cephalosporin
if history of anaphyaxsis, avoid administration of penicillin or cephalosporins

Question 17

Safe alternatives to PCN

Answer 17

vancomycin (glycopeptide class)
erythromycin (macrolide class)
clindamycin (lincomycin)

Question 18

Penicillinase-Resistant Penicillins

Answer 18

Broad Spectrum Penicillins (gram negative):
ampicillin
amoxicillin

Question 19

Adverse Effects of amoxicillin

Answer 19

rash
diarrhea

Question 20

Penicillin Combinations

Answer 20

beta lactamase inhibitors: clavulanic acid, tazobactam, sulbactam
sulbactam and clavulanate: make the antibiotics more effective against beta lactamase producing microbes; effective against more bugs
Ampicillin/sulbactam (Unasym) - IV
Amoxicillin/clavulanic acid (Augmentin) - PO
Piperacillin/tazobactam (Zosyn) - IV

Question 21

Staphylococus Aures

Answer 21

gram positive
mode of transmission - contact

Question 22

MOA Staphylococus Aureus

Answer 22

developed resistance to beta-lactam (which includes penicillins and cephalosporins) antibiotics by producing enzyme penicillinase —> converts to —> MRSA has a unique mechanism of resistance - produces (Penicillin binding proteins) PBPs with a low affinity for penicillins and all other beta lactam antibiotics

Question 23

Only cephalosporin effective in treating MRSA

Answer 23

Ceftaroline