Flucloxacillin

Flucloxacillin is a penicillin antibiotic with a narrow spectrum of activity that is specifically effective against Gram-positive organisms. It is indicated for the treatment of skin infections, external ear infections, leg ulcer infections, diabetic foot infections, and bone infections. It may be used with other medications to treat pneumonia and endocarditis. Flucloxacillin cannot be used for methicillin-resistant Staphylococcus aureus (MRSA) infections. It is administered orally or parenterally.

The substance was developed because of increasing bacterial resistance to established antibiotics. Flucloxacillin was patented in 1961 and was first marketed in Europe in the 1970s.

Pharmacodynamics

Like other β-lactam antibiotics, flucloxacillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linking between linear peptidoglycan polymer chains by binding to specific penicillin-binding proteins (PBPs) found in the bacterial cell wall. These peptidoglycan chains form a major component of the cell wall of Gram-positive bacteria. Inhibition prevents the bacteria from forming a stable cell wall and causes them to die.

Flucloxacillin is more acid stable than many other penicillins and can be administered orally in addition to parenteral administration.

Pharmacokinetics

The bioavailability of flucloxacillin is 50-70% after oral administration. It is metabolized in the liver. The half-life is approximately 0.75-1 h and the drug is ultimately excreted via the kidneys and urine.

Drug Interactions

Flucloxacillin may decrease the excretion of methotrexate, resulting in an increased risk of toxicity symptoms and increased side effects.

Flucloxacillin levels in the blood may increase in renal failure and with the use of probenecid, leading to increased side effects.

Side effects

Common side effects associated with the use of flucloxacillin include:

• Diarrhea
• Nausea
• Skin rash
• Urticaria
• Pain
• Injection site reactions
• Superinfection (including candidiasis)
• Temporary elevation of liver enzymes and bilirubin.

A less common side effect is cholestatic jaundice (jaundice).

Contraindications and precautions

Flucloxacillin is contraindicated in individuals allergic to penicillins, cephalosporins, or carbapenems. Flucloxacillin should also not be used on the eye or in individuals with a history of cholestatic hepatitis associated with the use of dicloxacillin or flucloxacillin.

Because of the risk of cholestatic hepatitis, it should be used with caution in the elderly, in patients with impaired renal function in whom a reduced dose is required, and in patients with impaired hepatic function, after careful consideration of the cost-benefit risk.

It should be taken on an empty stomach, one-half to one hour before food, as absorption is reduced when taken with food.