Antibiotics

Question 1

Indications for Phenoxymethylpenicillin /benzylpenicillin

Answer 1

1. Streptococcal infection
   e.g. Tonsillitis
   Pneumonia (with macrolide/tetracycline)
   Endocarditis (with gentamicin)
2. Neisserial infection (e.g. N.meningitides/N.gonorrhoea)
3. Clostridial infection (gas gangrene)

Question 2

Phenoxymethylpenicillin (Pen V) vs benzylpenicillin (Pen G)

Answer 2

Pen V: less severe infections, can be given orally
Pen G: severe infections, hydrolysed by gastric acid so can only be given IM/IV

both are narrow spec (active against gram +ve cocci, some -ve cocci not bacilli

Question 3

Adverse effects

of pen V and pen g

Answer 3

IgG-mediated skin rash (2-3d after repeated doses, 7-10d after initial dose)
IgE-mediate anaphylactic reaction
Neurological toxicity (convulsions, coma)

Question 4

Interaction with MTX

with pen v and pen g

Answer 4

Both renally excreted
Avoid with MTX : reduces excretion of MTX, causes mtx toxicity

Question 5

EBV in a child - which antibiotic?

Answer 5

Pen V

Avoid amoxicillin - can develop rash mistaken for allergy