Antibiotics: Penicillin

Question 1

Indications of penicillins?

Answer 1

Streptococcal infection, including:​
- Tonsilitis​
- Pneumonia (+ macrolide/ tetracycline)​
- Endocarditis (+ gentamicin)​
- Skin and soft tissue infections (+ flucloxacillin)

Meningococcal infection including:​
- Meningitis​
- Septicaemia

Clostridial infection ​including:
- gas gangrene (clostridial myonecrosis)

Question 2

MOA of penicillins?

Answer 2

Inhibit the enzymes responsible for cross-linking peptidoglycans in bacterial cell walls.
→ This weakens cell walls and prevents them from maintaining an osmotic gradient.
→ Uncontrolled entry of water into bacteria causes: ​
- cell swelling​
- lysis ​
- death​

Contains beta-lactam ring
→responsible for bactericidal activity.

Bacteria can resist penicillins action by making β-lactamases, which break the β-lactam ring.

Question 3

Examples of penicillins?

Answer 3

Phenoxymethylpenicillin
Benzylpenicillin

Question 4

Spectrum of activity of penicillins?

Answer 4

Narrow antimicrobial spectrum

Works against some Gram-positive organism and Gram-negative cocci.

Does NOT work against Gram-negative bacilli (rods).

Question 5

Adverse effects of penicillins?

Answer 5

Penicillin allergy
- skin rash

Anaphylactic reaction
- hypotension
- bronchospasm
- orofacial/pharyngeal/laryngeal oedema

Neurological toxicity

Question 6

Warnings of penicillins?

Answer 6

Reduce dose for renal impairment.

Contraindicated in penicillin allergy.

Pts with immediate hypersensitivity to penicillins may also react to:​
- Cephalosporins​
- Other beta-lactam abx​

​

Question 7

Interactions of penicillins?

Answer 7

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

Question 8

Monitoring of penicillins?

Answer 8

Check infection resolves by:​
- symptoms/signs improved ​
- blood markers e.g. falling CRP and WCC

Question 9

Pt education of penicillins?

Answer 9

Aims to get rid of infection and improve symptoms.

Check for penicillin allergy.

Seek medical advice if they develop a rash.

If allergy develops during treatment, give pt written and verbal advice NOT to take this abx class in future and make sure that the type of reaction (including its nature) is clearly documented in pt’s medical records.