Penicillins - Benzyl/phenoxymethypenicillin

Question 1

What are common indications for benzylpenicillin/phenoxymethylpenicillin?

Answer 1

• Strep infections - tonsillitis, pneumonia, endocarditis, skin/soft tissue
• Tetanus
• Meningitis
• Septicaemia

Question 2

How do penicillins work?

Answer 2

Inhibit enzymes respinsible for cross-linking peptidoglycans in bacterial cell walls - weakens cell walls

Question 3

How do bacteria resist penicillins?

Answer 3

B-lactamases

Question 4

What proportion of individuals are affected by penicillin allergy?

Answer 4

1-10%

Question 5

How does penicillin allergy present?

Answer 5

• Skin rash 7-10 days after first exposure, or 1-2 days after repeat exposure.
• Can also present with anaphylaxis

Question 6

What are common side effects of penicillin?

Answer 6

• Allergy
• CNS toxicity - high doses

Question 7

When might you consider dose reduction with penicillins?

Answer 7

Renal impairment

Question 8

What important drugs which can interact with penicillins?

Answer 8

Methotrexate

Question 9

What can penicillins cause in someone who is taking methotrexate?

Answer 9

Methotrexate toxicity

Question 10

How is benzylpenicillin administered?

Answer 10

IM or IV - is hydrolysed by gastric acid

Question 11

What is phenoxymethylpenicillin also known as?

Answer 11

Penicillin V

Question 12

How can phenoxymethylpenicillin be given?

Answer 12

• Orally
• IM
• IV

Question 13

How might you monitor penicillin efficacy?

Answer 13

• Signs/symptoms
• Blood markers - CRP, WCC