Antibiotics_Penicillin_March 19

Question 1

What classes have a beta-lactam ring?

Answer 1

Penicillin

Cephalosporin

Question 2

What is the mechanism of action of beta lactams?

Answer 2

-Inhibit cell wall synthesis (preventing NAM cross links) by binding to penicillin binding protein

Question 3

What can cause resistance to beta-lactams?

Answer 3

• Modification of penicllin binding protein
• Efflux pump
• Beta-lactamase
• No access to PBP

Question 4

What are the two definitions of penicillin to be wary of?

Answer 4

Drug class penicillin
Drug named penicillin that is part of the overall drug class 
(quiz is focused on drug class)

Question 5

What is the oral bioavailability for benzyl penicillin and amoxicillin?

Answer 5

15% and 80% respectively (both considered well absorb, and represent the extreme ranges)

Question 6

How are penicillins cleared?

Answer 6

Renally

Question 7

Is the therepeutic index of penicillin wide or narrow?

Answer 7

-Wide

(lower side effects)–>don’t need to adjust much even for renal impairment

Question 8

What is the spectrum of action of the class?

Answer 8

-Very wide to very narrow depending on drug

Question 9

What safety considerations do you need to consider when prescribing?

Answer 9

• Allergies

- Hepatotoxicity (some drugs)

Question 10

What are the narrow spectrum penicillins? What do they act on?

Answer 10

• Benzyl penicillin (Pen G)
• Phenoxymethylpenicillin (Pen V)
• Benzathine penicillin (IM injection, for syphillis, 2 weeks)
• Procaine penicillin (daily intramuscular injection)

-Acts on gram + cocci
(pneumonococcus, streptococcus, meningococcus, syphillis, actinomycosis, listeria (yeah i’ll leave to you how much you want to memorise)
-Covers most oral flora

Question 11

What narrow spectrum penicillins can we use to treat staph infection? What are the risks?

Answer 11

• Flucloxacillin: risk of cholestatic jaundice

- Dicloxacillin

Question 12

What are the moderate spectrum penicillins? What are the risks?

Answer 12

-Amoxycillin: high risk of macular/papular rash when prescribed for glandular fever–>not contra for future use
-Ampicillin
(G+ cocci + some G-)

Question 13

What are the broad spectrum penicililns? What are the risks?

Answer 13

-Amoxycillin + clavulanate (clavulanate inhibits beta-lactamase)

• Has very good anaerobic coverage
• Higher risk of diarrhoea and hepatotoxicity

Question 14

What is a non-specific rash? If patient presents with it, should you prescribe the drug again?

Answer 14

• When experience rash as childhood, not sure how long it lasted, etc., just know it’s a rash
• 5% chance of reoccurrence
• Do not prescribe again as it can be uncomfortable if can be avoided, weigh up against adverse effects of alternatives

Question 15

What are the symptoms of type I hypersensitivitY?

Answer 15

• Hives (raised itchy areas)
• Shortness of breath
• Swelling
• Angioedema
• Anaphylaxis
• Collapse
• Death

Question 16

Waht would you do with a pt who claims to have previous hypersensitivity to penicillin?

Answer 16

• History: from patient, GP, parent
• Discern if it is type I hypersensitivity
• Usually assume worse and use other non-penicillin agent
• If low risk may use penicillin again + explain risk
• If low risk and pt tolerates, inform other health practitioners

Question 17

What drug class is used as a back up in case of penicillin allergy?

Answer 17

Cephalosporins (if confused about penicillin allergy but not sure)–>if true sensitivity risk of cross reaction
Lincosamides (used if true penicillin allergy)

Question 18

What other precaution do you ahve to take with penicillin?

Answer 18

-Advise not to take near a meal else decreased bioavailability due to binding to food