Fusidic acid

Fusidic acid is an antibiotic primarily used for the treatment of Gram-positive bacterial infections.

Approved Indications:

• Skin and Soft Tissue Infections: Impetigo, infected eczema, boils, cellulitis, abscesses caused by Staphylococcus aureus (including methicillin-sensitive strains).
• Osteomyelitis: In combination with systemic therapy for bone infections caused by susceptible bacteria.
• Ophthalmic Infections: Conjunctivitis and blepharitis caused by susceptible strains (Fusidic acid eye drops).
• Surgical Wound Infections: Prevention or treatment of post-operative infections.

Off-label / Clinically Accepted Uses:

• Chronic skin conditions with secondary bacterial infection: Such as diabetic ulcers and chronic wounds.
• Nasal carriage eradication: To reduce S. aureus colonization.

Topical Use (Skin):

• Apply a thin layer 2–3 times daily to the affected area.
• Duration: Usually 7–14 days, depending on clinical response.

Ophthalmic Use (Eye Drops/Ointment):

• 1 drop in the affected eye every 4–6 hours or as prescribed.
• Treatment duration: 7–10 days or until resolution of infection.

Oral/Parenteral Use (Severe Systemic Infections, Fusidic Acid Sodium):

• Adults: 500 mg orally every 8 hours or as per specialist guidance.
• Pediatrics: 15–25 mg/kg/day in divided doses, individualized by age and weight.

Special Populations:

• Renal Impairment: Generally no dose adjustment required; monitor for adverse effects.
• Hepatic Impairment: Use with caution; monitor liver function tests.
• Elderly: Standard dosing; monitor hepatic function and potential drug interactions.

Administration Routes: Topical (cream, ointment, gel), ophthalmic (eye drops/ointment), oral, intravenous.

Fusidic acid inhibits bacterial protein synthesis by interfering with the elongation factor G (EF-G) during the translation process. By binding to EF-G on the ribosome, it prevents the translocation of tRNA and mRNA, halting protein elongation. This action is bacteriostatic against susceptible Gram-positive organisms, primarily Staphylococcus aureus, and prevents bacterial proliferation, allowing the immune system to eradicate the infection.

Topical Application:

• Minimal systemic absorption; peak plasma levels usually negligible.

Oral/Parenteral Administration:

• Absorption: Rapid oral absorption; bioavailability 90–100%.
• Distribution: Widely distributed in tissues, especially skin, bone, and synovial fluid; high protein binding (97–99%).
• Metabolism: Primarily hepatic via glucuronidation.
• Elimination: 60–75% via bile and feces, 10–15% via urine.
• Half-life: 5–6 hours (prolonged in hepatic impairment).

• Pregnancy: Category B; animal studies show no teratogenic effects, but human data are limited. Use only if clearly needed.
• Lactation: Excreted in breast milk in small amounts; caution advised. Monitor the infant for gastrointestinal disturbances or allergic reactions.

• Primary Class: Antibiotic
• Subclass: Fusidane class / protein synthesis inhibitor

• Known hypersensitivity to fusidic acid or any formulation excipients.
• Use with caution in severe liver disease (for systemic formulations).

• Resistance Risk: Avoid prolonged use or monotherapy for systemic infections to reduce resistance development.
• Hepatic Monitoring: Required for systemic administration, especially in pre-existing liver disease.
• Allergic Reactions: Rash, pruritus, or anaphylaxis; discontinue if severe.
• Topical/Ophthalmic Use: Avoid contact with eyes (for skin formulations) or prolonged use without supervision.

Common:

• Skin: Irritation, redness, itching
• Eyes: Mild stinging or burning with drops/ointment
• Gastrointestinal: Nausea, diarrhea (systemic use)

Serious / Rare:

• Hepatotoxicity: Elevated liver enzymes, jaundice
• Blood disorders: Rare neutropenia or thrombocytopenia (systemic use)
• Hypersensitivity reactions: Rash, urticaria, anaphylaxis

Timing & Dose Dependence:

• Topical: Usually mild and appears within days.
• Systemic: Dose-related hepatotoxicity or GI disturbances may develop over days to weeks.

• CYP3A4 Substrates: Systemic fusidic acid can inhibit CYP3A4, increasing serum levels of co-administered drugs like statins or warfarin.
• Statins (e.g., Simvastatin): Risk of rhabdomyolysis; avoid concurrent use if possible.
• Warfarin: Increased anticoagulant effect; monitor INR.
• Other antibiotics: Concurrent bacteriostatic antibiotics may antagonize activity; monitor efficacy.

• Topical fusidic acid remains first-line for mild to moderate S. aureus skin infections.
• Caution advised for prolonged use due to increasing reports of methicillin-resistant S. aureus (MRSA) resistance.
• Guidelines emphasize limiting systemic use to confirmed susceptible infections and monitoring liver function for oral or IV formulations.

• Store at 20°C to 25°C in a dry, light-protected area.
• Topical and ophthalmic forms: Keep tightly closed; avoid contamination.
• Protect from freezing and excessive heat.
• Discard eye drops/ointment after the manufacturer’s recommended period once opened.