INFECTIONS: PENICILLINS

Question 1

PENICILLINS: INDICATIONS

Answer 1

• Streptococcal infection, including tonsillitis, pneumonia (in combination with a macrolide if severe), endocarditis and skin and soft tissue infections (added to flucloxacillin if severe).
• Clostridial infection, for example tetanus.
• Meningococcal infection, for example meningitis, septicaemia

Question 2

PENICILLINS: MOA

Answer 2

• Penicillins inhibit the enzymes responsible for cross-linking peptidoglycans in bacterial cell walls
• This weakens cell walls, preventing them from maintaining an osmotic gradient
• Uncontrolled entry of water into bacteria causes cell swelling, lysis and death
• Penicillins contain a β-lactam ring, which is responsible for their antimicrobial activity
• Side chains attached to the β-lactam ring can be modified to make semi-synthetic penicillins
• The nature of the side chain determines the antimicrobial spectrum and other properties of the drug.

Question 3

PENICILLINS: ADVERSE EFFECTS

Answer 3

• Penicillin allergy
• This usually presents as a skin rash 7–10 days after first exposure or 1–2 days after repeat exposure (subacute [delayed] IgG-mediated reaction)
• Less commonly, an immediate (minutes to hours) life-threatening IgE-mediated anaphylactic reaction occurs with some or all of hypotension, bronchial and laryngeal spasm/oedema and angioedema
• Central nervous system toxicity (including convulsions and coma) can occur with high doses of penicillin or where severe renal impairment delays excretion

Question 4

PENICILLINS: WARNINGS

Answer 4

• Dose reduction required in renal impaired patients

- Main CI to penicillin use if a Hx of penicillin allergy

Question 5

PENICILLINS: INTERACTIONS

Answer 5

• Reduce renal excretion of MTX, increase risk of toxicity

Question 6

PENICILLINS: EXAMPLES

Answer 6

• benzylpenicillin

- phenoxymethylpenicillin