CLASSES OF ABX: PENICILLINS

Question 1

Narrow spectrum penicillins

Answer 1

(Beta-lactamase sensitive)

• Benzylpenicillin (Penicillin G),
• Phenoxymethylpenicillin (Penicillin V)

Question 2

Benzylpenicillin (Penicillin G)

Answer 2

o Not gastric stable
o Parenteral use only

Question 3

Phenoxymethylpenicillin (Penicillin V)

Answer 3

o Gastric acid stable
o Suitable for oral administration

Question 4

Broad-spectrum penicillins

Answer 4

(but inactivated by beta-lactamases)

• Amoxicillin, Ampicillin
  o Co-amoxiclav – beta-lactamase resistance

Question 5

Penicillinase-resistant penicillins

Answer 5

Flucloxacillin

Question 6

Flucloxacillin counselling points

Answer 6

To be taken on an empty stomach. An hour before food or 2hrs after food.

Question 7

Flucloxacillin: cholestatic jaundice and hepatitis

Answer 7

may occur very rarely
o Up to 2 months after treatment with flucloxacillin has been stopped
o Administration for more than 2 weeks nad increasing age are risk factors

Question 8

Antipseudomonal penicillin

Answer 8

HOSPITAL
* Piperacillin only available in combination with beta-lactamase inhibitor tazobactam
* Ticarcillin only available in combination with beta-lactamase clavulanic acid

Question 9

MOA

Answer 9

• Penicillins are bactericidal beta-lactam antibiotics that inhibit bacterial cell wall synthesis by inhibiting peptidoglycan cross-linking.
• They diffuse well into body tissues and fluids, but penetration into the cerebrospinal fluid is poor except when the meninges are inflamed.

Question 10

Activity against

Answer 10

Gram +
some Gram - cocci

Question 11

Indications

Answer 11

• Oral infections
• Otitis media
• Cellulitis
• Respiratory tract infections
• Pneumonia.

Question 12

Side effects

Answer 12

• Hypersensitivity (1-10% of exposed individuals)
• Anaphylaxis (<0.05%)
• Penicillin allergy
• Diarrhoea (with broad spectrum)
• CNS toxicity
• Hepatic disorders may occur rarely with flucloxacillin.
• Maculopapular rashes commonly occur in patients with glandular fever

Question 13

Penicillin allergy (true allergy)

Answer 13

o True allergy = immediate rash –> anaphylaxis

Question 14

May not be an allergy

Answer 14

minor rash, small, not itchy and non-confluent
or rash after 72 hours

Question 15

Patients allergic to one penicillin may be allergic to all

Answer 15

o hypersensitivity can be related to the basic penicillin structure
o caution should be used in severe allergy with cephalosporins and other beta-lactam antibiotics.

Question 16

Penicillin resistance

Answer 16

caused by beta-lactamase (enzyme which targets beta-lactam ring) existing within the infective organism.

Question 17

CNS toxicity

Answer 17

a rare but serious side-effect encephalopathy due to cerebral irritation

Question 18

Diarrhoea (with broad spectrum)

Answer 18

Which can cause antibiotic- associated colitis

Question 19

maculopapular rashes commonly occur in patients with glandular fever

Answer 19

o Do not use broad spectrum penicillin blindly for sore throat
o Make sure its not glandular fever before giving pen v
o Common with ampicillin and amoxicillin.

Question 20

Giving penicillins intrathecally

Answer 20

Do NOT give intrathecally = CNS toxicity