Clinical beta
FMBM is currently in clinical beta. Content is for professional review/testing and must not replace local protocols, senior clinical judgment, or official prescribing references.
Drug Monograph
Flucloxacillin
Penicillinase-resistant antistaphylococcal penicillin
Indication
MSSA skin/soft tissue infection β’ MSSA bone/joint infection β’ MSSA bacteremia/pneumonia β’ Streptococcal SSTI when appropriate
INDICATIONS (CORE USE)
MSSA skin/soft tissue infection β’ MSSA bone/joint infection β’ MSSA bacteremia/pneumonia β’ Streptococcal SSTI when appropriate
ADULT DOSE (STANDARD)
Oral: 500 mg PO q6h IV: 1β2 g IV q4β6h
MAX DOSE
Max: 12 g/day IV (adjust in severe renal impairment per labeling)
Route
PO, IV, IM
PEDIATRIC DOSE
25β50 mg/kg/dose q6h PO/IV β Severe: up to 100 mg/kg/dose IV q6h per local protocol
Must-not-miss safety points
Major warning
- Hypersensitivity (anaphylaxis risk) - No MRSA coverage β DO NOT use if MRSA suspected or confirmed - Not active against MRSA β confirm MSSA before use in severe infection - Delayed cholestatic hepatitis may occur weeks after stopping therapy β monitor LFTs if symptoms - High sodium load (IV) β caution in heart failure, CKD, and ICU patients - Flucloxacillin + paracetamol can cause high anion gap metabolic acidosis (5-oxoproline), especially with sepsis, malnutrition, renal impairment, or prolonged use - Risk increases with prolonged use (>2 weeks) and older age - High-dose IV: hypokalemia, AKI, neurotoxicity risk - PO absorption reduced by food β empty stomach preferred - Gram-negative/polymicrobial infection requires added coverage β not reliable monotherapy
USE IF: MSSA skin/soft tissue infection; MSSA bone/joint infection; MSSA bacteremia / pneumonia; streptococcal SSTI when a penicillinase-resistant antistaphylococcal Ξ²-lactam is appropriate. AVOID IF: MRSA (or high MRSA likelihood without adequate coverage); gram-negative or polymicrobial infection without added agents; prior flucloxacillin cholestatic hepatitis. Narrow-spectrum isoxazolyl penicillinβmatch to confirmed or high-probability MSSA and monitor liver function with prolonged therapy.
ADULT DOSE
PO: 500 mg q6h IV: 1β2 g q4β6h Severe MSSA: Up to 2 g IV q4h Step-down: 500 mg PO q6h
PEDIATRIC DOSE
25β50 mg/kg/dose q6h PO/IV. Severe infections: up to 100 mg/kg/dose IV q6h per local protocol.
MAX DOSE
Max adult dose: 12 g/day IV β titrate in severe renal impairment per product monograph.
Practical Note
- Renal adjustment usually not required β only modify in severe renal impairment (CrCl <10 mL/min: reduce dose or extend interval; some labels cap at 1 g q8β12h) - Deep MSSA infection / endocarditis requires high-dose IV therapy β do not underdose severe infection; ensure guideline-level dosing (e.g., 2 g IV q4β6h) - Hepatic: no formal algorithm; avoid prolonged/high-dose if significant liver disease; stop if hepatitis/cholestasis - PO: best on empty stomach (1 h before or 2 h after food) - Switch IV β PO once clinically stable and improving
Clinical warnings
Adverse effects
Pediatrics
25β50 mg/kg/dose q6h PO/IV β Severe: up to 100 mg/kg/dose IV q6h per local protocol
Pregnancy
Generally safe in pregnancy when indicated; monitor LFTs with prolonged courses. Breastfeeding usually compatible β observe infant for GI symptoms and rash. Pregnancy: Generally safe; monitor LFTs if prolonged therapy.
Lactation
Compatible β monitor infant for diarrhea, rash, candidiasis.
Renal impairment
Mildβmoderate impairment: usually standard dosing. Severe impairment: reduce dose or extend interval; monitor neurotoxicity and electrolytes with high-dose IV.
Hepatic impairment
No formal dose reduction; use extreme caution. Baseline and serial LFTs for prolonged courses.
Elderly
Higher cholestatic hepatitis risk; monitor LFTs and renal function closely.
Give on empty stomach (1 h before or 2 h after food). PO: capsules/suspension. IV or IM: sodium salt β intermittent IV 1β2 g over 30β60 min per protocol; continuous infusion may be used in ICU for severe MSSA infection. IM: deep IM if IV not available. Prefer IV initially for serious infection, then step down to PO when clinically stable.
Clinical Picture
No well-defined toxic threshold; toxicity increases with high doses or renal impairment. Features: confusion, agitation, seizures; rising creatinine; hypokalemia; hypernatremia / sodium overload; cholestatic hepatitis.
Immediate Actions
- Stop flucloxacillin immediately - Supportive care
Antidote
No specific antidote β supportive care
Decontamination
Massive oral ingestion β contact poison center; charcoal rarely indicated.
Escalation
Benzodiazepines for seizures; correct electrolytes and fluid balance; stop drug if hepatitis suspected β monitor LFTs/INR; consider renal replacement for severe AKI or neurotoxicity per nephrology.
Common mistakes, resistance logic, and bedside traps
FIRST LINE: Narrow-spectrum anti-MSSA Ξ²-lactam for staph skin, bone, joint, and bloodstream infection. DOSE β Oral: 500 mg PO q6h; IV: 1β2 g IV q4β6h. MAX β 12 g/day IV. AVOID β MRSA; severe liver toxicity history from flucloxacillin; high-dose in severe renal failure without adjustment. ANTIDOTE β None.
- Max adult dose: 12 g/day IV - Delayed cholestatic hepatitis can occur during or weeks after therapy - Stop immediately if jaundice, pruritus, dark urine, or major LFT rise - Confirm MSSA β ineffective for MRSA - Consider switch to cefazolin if IV intolerance or frequent dosing is impractical - High-dose IV: hypokalemia, sodium load, AKI, neurotoxicity - Best absorbed on empty stomach - Deep MSSA infection usually needs full-dose IV first, not oral alone
First-line for MSSA infections β preferred over broader-spectrum agents when MRSA risk is low. Do not use alone for polymicrobial diabetic foot or mixed wound infection unless additional coverage is added. For deep MSSA infection, oral therapy alone is usually inadequate initially. In patients >55 years or on >14-day courses, liver monitoring is critical. New jaundice after flucloxacillin = drug-related until proven otherwise. 3 AM check: MSSA confirmed? Renal function okay? LFTs current? IV-to-PO plan documented?
- Oral bioavailability ~50β70% - Absorption reduced by food - Partial hepatic metabolism - Mainly renal elimination with some biliary excretion - Half-life ~0.75β1 h - Prolonged half-life in elderly and renal impairment
Penicillinase-resistant isoxazolyl penicillin. Binds penicillin-binding proteins and inhibits peptidoglycan cross-linking. Active against MSSA and some streptococci. Not active against MRSA or most gram-negatives.
Saudi Arabia
Flucloxacillin (generic)
Global
Flucloxacillin (manufacturer generic), Flucloxacillin sodium (regional generics), Flucloxacillin sodium (generic), Local flucloxacillin sodium products
Common trade names are curated examples only β formulations and availability vary. Verify the exact product name with your local pharmacy and national regulator before prescribing or dispensing.
Saudi Arabia
International