Flucloxacillin

Question 1

Flucloxacillin - indications

Answer 1

Staphylococcal infection, usually as part of combination therapy, including:

• Skin and soft tissue infections such as cellulitis.
• Osteomyelitis and septic arthritis.
• Other infections, including endocarditis.

Question 2

Flucloxacillin - MOA and why is flucloxacillin known as a penicillinase-resistant penicillin?

Answer 2

1. β-lactamases (penicillinase) are enzymes produced by bacteria to deactive penicillin - this makes certain bacteria resistant to certain penicillins

So, how does flucloxacillin overcome this resistance?
2. Flucloxacillin is a penicillinase-resistant antibiotic - has an acyl side chain which protects the β-lactam ring from β-lactamases (the enzymes made by bacteria to deactivate penicillin)

3. Therefore, flucloxacillin is effective against β-lactamase-producing staphylococci

Flucloaxacillin can then target the bacteria as normal (same as penicillin MOA)

1. Penicillin inhibits the enzymes responsible for cross-linking peptidoglycans in bacterial cell walls.
2. weakens cell walls = uncontrolled entry of water into bacteria = cell swelling, lysis and death.

Question 3

Flucloxacillin - spectrum?

Answer 3

narrow spectrum - against Gram(+) staphylococci

Question 4

Flucloxacillin - adverse effects

Answer 4

1. minor GI upset: diarrhoea, nausea (most common)
2. Penicillin allergy: Skin rash, Anaphylactic reaction
3. Hepatic toxicity: cholestasis and hepatitis (rare but serious)

Question 5

Flucloxacillin - caution in patients with..

Answer 5

renal failure

hepatic impairment

Question 6

Flucloxacillin - contraindicated in patients with..

Answer 6

Hx of penicillin allergy

Hx of penicillin-associated hepatotoxicity

Question 7

Flucloxacillin - interactions

Answer 7

methotrexate

why? reduces renal excretion of methotrexate - increasing risk of toxicity