INFECTIONS: PENICILLIN, BROAD SPEC

Question 1

PENICILLINS, BROAD SPEC: INDICATIONS

Answer 1

• Empirical tx of Pneumonia (Strep B, HI)
• Empirical tx of UTI (most commonly caused by E.Coli, Trimethoprim and Nitrofurotonin used commonly)
• As part of combination treatment (as co-amoxiclav) for hospita lacquired infection or intra-abdominal sepsis, which may be caused by Gram-negative and anaerobic pathogens or antibiotic-resistant organisms
• As part of combination treatment for H. pylori-associated peptic ulcers.

Question 2

PENICILLINS, BROAD SPEC: 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. For amoxicillin, addition of an amino group to the side chain increases activity against aerobic Gram-negative bacteria, making this a ‘broad-spectrum’ antibiotic.
• Addition of the β-lactamase inhibitor clavulanic acid (creating co-amoxiclav) increases the spectrum of antimicrobial activity further to include β-lactamase-producing bacteria (e.g. Staphylococcus aureus, Gram-negative anaerobes

Question 3

PENICILLINS, BROAD SPEC: ADVERSE EFFECTS

Answer 3

• GI upset - nausea, diarrhoea
• Antibiotic associated colitis when broad spec antibiotics kill normal gut flora causing an overgrowth of C.Diff => can be complicated by colonic perforation and/or death
• Penicillin allergy => 1-10% of people
• This usually presents as a skin rash 7–10 days after first or 1–2 days after repeat exposure (delayed IgG-mediated reaction)
• Less commonly, an immediate (minutes to hours) life threatening IgE-mediated anaphylactic reaction occurs with features including hypotension, bronchospasm and angiooedema.
• Cholestatic jaundice is a rare adverse effect of co-amoxiclav

Question 4

PENICILLINS, BROAD SPEC: WARNINGS

Answer 4

• People at risk of C.Diff infection (hospital and elderly)
• Hx of penicillin allergy (allergy to one type, means allergy to all types due tto rxn to basic penicillin structure)
• Dose reduction in patients with severe renal impairment (risk of crystalluria)

Question 5

PENICILLINS, BROAD SPEC: INTERACTIONS

Answer 5

• MTX

- Warfarin

Question 6

PENICILLINS, BROAD SPEC: EXAMPLES

Answer 6

• Amoxicillin

- Co-amoxiclav