1 Penicillins: Benzylpenicillin, phenoxymethylpenicillin

Question 1

what are the indications for benzylpenicillin and phenozymethylpenicillin? (beta-lactamase sensitive)

Answer 1

1) Streptococcal infection, including tonsillitis, pneumonia
2) Endocarditis (usually with gentamicin) and skin and soft tissue infections (with flucloxacillin).
3) Meningococcal infection e.g. meningitis, septicaemia.
Clostridial infection, for

Question 2

what is the spectrum of activity for Benzylpenicillin and phenoxymethylpenicillin?

Answer 2

1) Relatively narrow antimicrobial spectrum, with activity against some Gram-positive organisms and Gram-negative cocci
2) Not active against Gram-negative bacilli (rods)
3) Antimicrobial spectrum is relatively narrow, they are often combined with other antibiotics

Question 3

outline the MoA of Benzylpenicillin and phenoxymethylpenicillin?

Answer 3

1) bactericidal

2) Prevent peptidoglycan cross-linking → Inhibit bacterial cell wall synthesis

Question 4

list some of the adverse effects caused by Benzylpenicillin and phenoxymethylpenicillin?

Answer 4

1) Penicillin allergy affects 1–10%. Usually presents as a skin rash 7–10 days after first exposure or 1–2 days after repeat exposure (subacute IgG-mediated)
2) Less commonly an immediate life-threatening IgE-mediated anaphylactic reaction occurs: hypotension, bronchospasm, and pharyngeal and laryngeal oedema.
3) Neurological toxicity (convulsions and coma) can with very high-doses or accumulation due to severe renal impairment.

Question 5

who should Benzylpenicillin and phenoxymethylpenicillin be used in caution with?

Answer 5

1) dose reduction in renal impairment.

2) penicillin allergy- Allergy to all penicillins , also may react to cephalosporins and other β-lactam antibiotics

Question 6

Outline some of the interactions with regards to penicillins?

Answer 6

All penicillins reduce renal excretion of methotrexate, increasing the risk of toxicity.

Question 7

how are benzylpenicillin and phenoxymethylpenicillin administered

Answer 7

1) Benzylpenicillin- (IV or IM) only, as hydrolysis by gastric acid prevents GI absorption. used for serious infections
2) Phenoxymethylpenicillin- stable in the presence of gastric acid and so can be taken orally as tablets or in solution. Not for serious infections because absorption can be unpredictable

Question 8

Where antibiotics are required to treat a young person with a sore throat caused by an unknown organism, which penicillin would be selected?

Answer 8

phenoxymethylpenicillin, not amoxicillin- If the sore throat is due to Epstein–Barr virus (glandular fever), amoxicillin treatment commonly causes a rash.

Question 9

what is Benzathine benzylpenicillin indicated for?

Answer 9

treatment of early syphilis and late latent syphilis; it is given by intramuscular injection

Question 10

what is Phenoxymethylpenicillin commonly used in the treatment and prevention of?

Answer 10

1) respiratory-tract infections in children, for streptococcal tonsillitis
2) prophylaxis against streptococcal infections following rheumatic fever and against pneumococcal infections following splenectomy or in sickle-cell disease