Penicillins

Question 1

What are the generic and brand names of penicillins?

Answer 1

• Benzylpenicillin

* Phenoxymethylpenicillin (Penicillin VK)

Question 2

What is the method of action of penicillins?

Answer 2

• B lactam rings inhibits the enzymes responsible for cross linking peptidoglycan in the bacteria cell walls
• = Weakened cell walls so cannot maintain an osmotic gradient

Question 3

What are the indications for penicillins?

Answer 3

• Streptococcal infection e.g. tonsillitis, pneumonia, endocarditis and skin/soft tissue infections
• Clostridial infection e.g. tetanus
• Meningococcal infections e.g. meningitis, septicaemia

Question 4

What are the contraindications for penicillins?

Answer 4

• Renal impairment – dose ↓

* History of penicillin allergy

Question 5

What are the side effects of penicillin?

Answer 5

• Penicillin allergy – skin rash (IgG mediated) → anaphylactic reaction (IgE)
• Central nervous system toxicity – inc. convulsions and coma can occur with high doses/severe renal impairment

Question 6

What drugs interact with penicillin?

Answer 6

• Methotrexate - ↓ renal excretion by penicillin

Question 7

What organ eliminates penicillin?

Answer 7

• Kidney

Question 8

What extra information should be taken into consideration when prescribing penicillins?

Answer 8

• If treating a young person with a sour throat caused by an unknown organism, give phenoxymethylpenicillin NOT amoxicillin
• If the sore throat is due to Epstein-Barr virus (glandular fever) then amoxicillin commonly causes a rash