Community Based Medicicne - Antibiotics in URTIs

Question 1

Benzylpenicilins (penecillin G), phenoxypenicillin (penicillin V)

Answer 1

MECHANISM OF ACTION

• B-Lactams block bacterial cell walls and inhibit the enyme responsible for cross linking peptidoglycan in bacterial cell. This weakens the cell wall preventing them from osmotic gradient
• Diffuse well into the body tissue and fluid, penetration into CSF is poor
• Excreted in urine in therapeutic concentrations

Question 2

Benzylpenicilins (penecillin G), phenoxypenicillin (penicillin V) - Dose

Answer 2

• Benzylpenicillin (penicillin G) - hydrolysis of gastric juices prevent GI absorption
• IV/IM 1.2g every 4-6 hours
• Phenoxymethylpenicillin (penicillin V) - orally adults 500mg 6hrly (inc if nec)

Question 3

Benzylpenicilins (penecillin G), phenoxypenicillin (penicillin V) -Side FX

Answer 3

• Allergy and cross sesitivity, 30% of people have penicillin allergy,can be fatal
• (anaphylactic reaction- brochospasm, hypotension, rash angiodema)
• CNS toxicity - encephalopathy, convulsion, coma can occurin high doses or where severe renal impaiment can delay excretion
• Patient with hypersensitivity with penicillinmay also react to other B-lactams, including cephalosporins, Carbopenem

Question 4

Benzylpenicilins (penecillin G), phenoxypenicillin (penicillin V) - Warnings

Answer 4

• Dose reduction for patients with renal impaiment
• History of allergy
• Accumulation of sodium from injection can cause renal failure
• High dose can cause neurotoxicity including cerebral irritation,convulsion and coma
• Penicillin can reduce renal excretion of methtrexate increasing toxicity risk