Flucloxacillin
Heracillin · Flukloxacillin Viatris
The beta-lactamase-stable penicillin and accordingly the first-line choice for skin and soft tissue infections where Staphylococcus aureus is the likely pathogen — wound infection, abscess, furuncle, mastitis, and infected eczema. Absorption is destroyed by food, making the timing of administration a genuine treatment variable and not a formality. The most clinically important adverse effect is delayed: cholestatic liver injury can present several weeks after the course has ended.
Cholestatic hepatitis with jaundice and prolonged pruritus can develop up to six weeks after completing treatment; the risk increases with age and duration of therapy. At high doses, severe, replacement-refractory hypokalaemia also occurs.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Skin and soft tissue infection with staphylococcal aetiology | 1 g × 3 orally for 7–10 days | wound infection, infected eczema, furuncle, abscess after drainage |
| Erysipelas with uncertain aetiology or wound entry | 1 g × 3 orally for 10 days | uncomplicated erysipelas is streptococcal and treated with phenoxymethylpenicillin |
| Mastitis | 1 g × 3 orally for 7–10 days | breastfeeding should continue — emptying is part of the treatment |
| Impetigo with widespread spread | Children 25 mg/kg × 3 orally for 7 days | topical treatment is sufficient for limited lesions |
| Osteomyelitis and septic arthritis, oral step-down | 1–1,5 g × 3 orally, daily dose up to 6 g | after initial intravenous treatment, in consultation with an infectious diseases specialist |
No adjustment in mild to moderate renal impairment. At eGFR below 10 ml/min the daily dose is reduced — high-dose treatment in severe renal failure increases the risk of neurotoxicity and hypokalaemia.
Avoid in patients with a previous episode of flucloxacillin-induced liver injury — re-exposure is contraindicated. In known liver disease, liver tests should be monitored during and after the course.
30–50 mg/kg per day divided into 3 doses, that is 10–17 mg/kg per dose; in more pronounced infection 25 mg/kg × 3. Available as powder for oral suspension 50 mg/ml. The same meal-timing rule applies in children.
Wrong choice for uncomplicated erysipelas without a wound entry — the infection is streptococcal and phenoxymethylpenicillin has both better efficacy and a milder adverse effect profile. Also avoid prescribing the tablet with a meal: absorption falls substantially, and a treatment failure that looks like resistance is in practice almost always incorrect timing rather than the pathogen.
Pharmacokinetics
- BIOAVAIL.
- Good — but markedly reduced by food
- t½
- 80–90 minutes
- PROTEIN BINDING
- 94–95 %
- METABOLISM
- Limited hepatic
- EXCRETION
- Renal, tubular secretion, 50–55 % in 6 hours
- ADMINISTRATION
- At least 1 hour before or 2 hours after a meal
- PK/PD INDEX
- T > MIC
- BETA-LACTAMASE
- Stable against staphylococcal penicillinase