Flucloxacin

# Flucloxacin ## Overview - **Classification**: Penicillinase-resistant penicillin (isoxazolyl penicillin), Beta-lactam antibiotic. - **Mechanism**: Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), leading to bacterial lysis. Bactericidal. ## Primary Indications 1. **Staphylococcal Infections**: Skin & soft tissue, bone & joint, endocarditis, septicaemia. 2. **Otitis Externa**: Often due to _S. aureus_. 3. **Pneumonia**: Caused by penicillinase-producing staphylococci. ## Adult Dosing ### Standard Dosing **Mild-Moderate Infections (e.g., Cellulitis, Abscess)** - **Dose**: **250-500 mg** - **Frequency**: Four times daily (QID) - **Route**: Oral (PO) or Intravenous (IV) - **Duration**: Typically 5-10 days for skin/soft tissue, longer for bone/joint. **Severe Infections (e.g., Endocarditis, Osteomyelitis)** - **Dose**: **1-2 g** - **Frequency**: Four times daily (QID) - **Route**: Intravenous (IV) - **Duration**: **4-6 weeks** for osteomyelitis/endocarditis. - **Max Dose**: Oral **4 g/day**; IV **12 g/day**. ### Dose Adjustments - **Renal Impairment**: - **CrCl >10 mL/min**: No dose adjustment needed. - **CrCl <10 mL/min (or on hemodialysis)**: Max **1 g** every 8-12 hours. Monitor carefully. - **Hepatic Impairment**: Use with caution. No specific dose reduction but increased risk of cholestatic hepatitis. - **Elderly Patients**: No specific adjustment based on age alone. Consider renal/hepatic function. ## Pediatric Dosing ### Neonates (0-28 days) - **Dose (IV/PO)**: - **0-7 days (low birth weight <2 kg)**: **25 mg/kg** - **0-7 days (full term)**: **25 mg/kg** - **8-28 days**: **25 mg/kg** - **Frequency**: - **0-7 days (low birth weight)**: Twice daily (BD) - **0-7 days (full term)**: Three times daily (TDS) - **8-28 days**: Four times daily (QDS) - **Maximum**: Neonatal maximums vary; generally **100 mg/kg/day** for severe infections. - **Special Notes**: Consider gestational age and postnatal age for optimal dosing. ### Infants (1-12 months) - **Dose**: **12.5-25 mg/kg** - **Frequency**: Four times daily (QID) - **Maximum**: **500 mg/dose**. Daily max up to **200 mg/kg/day** for severe infections. ### Children (1-12 years) - **Dose**: **12.5-25 mg/kg** - **Frequency**: Four times daily (QID) - **Maximum**: **500 mg/dose**. For severe infections, up to adult dose (e.g., **1 g** QID). Daily max **4 g**. ### Adolescents (13-18 years) - **Dose**: Adult dosing typically applies. - **Maximum**: Oral **4 g/day**; IV **12 g/day**. ## Safety Information ### Contraindications - **Absolute**: Hypersensitivity to penicillin antibiotics (e.g., rash, anaphylaxis). - **Absolute**: History of flucloxacillin-associated cholestatic jaundice/hepatic dysfunction. - **Relative**: Severe renal impairment (CrCl <10 mL/min) requires dose adjustment. ### Common Adverse Effects - **Common (1-10%)**: Nausea, vomiting, diarrhea, abdominal discomfort. - **Common (1-10%)**: Skin rash (maculopapular), urticaria. - **Serious but Rare**: Anaphylaxis, angioedema, Clostridioides difficile infection (CDI). - **Serious but Rare**: Cholestatic hepatitis/jaundice (can be delayed weeks after treatment). - **Serious but Rare**: Neutropenia, thrombocytopenia, interstitial nephritis. ### Key Drug Interactions - **Warfarin**: May enhance anticoagulant effect. **Monitor INR closely**, adjust warfarin dose. - **Methotrexate**: May reduce methotrexate excretion. **Monitor for methotrexate toxicity**. - **Oral Contraceptives**: Theoretical reduction in efficacy. Advise additional contraception. - **Probenecid**: Increases flucloxacillin levels. **Avoid concomitant use** if high flucloxacillin levels are undesirable. ## Monitoring & Follow-up - **Before Treatment**: Assess for penicillin allergy. Consider baseline LFTs if pre-existing hepatic disease. - **During Treatment**: - **LFTs**: Periodically for prolonged courses (>2 weeks) or high doses. - **Renal Function**: For prolonged courses or in patients with renal impairment. - **Clinical Signs**: Monitor for rash, fever, jaundice, dark urine, or unusual bruising/bleeding. - **Clinical Signs**: Jaundice (yellowing of skin/eyes) or severe abdominal pain warrant immediate medical review. ## Clinical Pearls - 💡 **Administration**: Oral doses should be given **30-60 minutes before meals** for optimal absorption. - 💡 **Not for MRSA**: Flucloxacin is **not effective against MRSA**. - 💡 **IV Dilution**: Administer IV doses slowly (over 3-4 minutes) or as an infusion to prevent vein irritation. - 💡 **Hepatic Risk**: Counsel patients on the delayed risk of cholestatic hepatitis, which can occur weeks after treatment. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.