Mupirocin

Nature

• Fermentation product of Pseudomonas fluorescence.

Mechanism of action

• Mupirocin inhibits bacterial protein synthesis by binding reversibly to the bacterial isoleucyl transfer-RNA synthetase enzyme. This mechanism is unique; hence, no cross-resistance with other antibiotics has been reported.
  It prevents bacterial protein synthesis.

Mechanism of resistance

• Low-level resistance (MIC 8-256) – Low-level resistance is chromosomal; it is due to point mutation in ileS gene. This gene codes for isoleucyl tRNA synthetase.

• High-level resistance (MIC>512) – Plasmid;  mupA gene mediated – which generates additional isoleucyl tRNA transferase.
• The risk of resistance is higher in cases of – long-term use, use in the presence of a foreign body (NG tube), and decubitus ulcer.

 PK/PD

• Inactivated in plasma, and hence it is only used topically.
• Bacteriostatic near MIC and bactericidal at higher concentrations.
• Poorly absorbed when used topically, absorbed drugs get metabolised in the liver.

Spectrum

• Staph aureus (including MRSA, VISA, VRSA), strep, CoNS, Enterococci, and Streptococcus bovis have high MIC,
• Micrococcus resistant. Corynebacterium and anaerobic gram positives are resistant.
• Haemophilus, Moraxella, Neisseria, Bordetella, Pasteurella sensitive.

Adverse effect

• Burning, stinging, itching, rash, headache.
• Mupirocin prep containing polyethylene glycol should be used with caution in renal impairment.

Use

• Eradication regimen for MRSA – anterior nares BD X 5 days. [Cochrane review 2008]
• NOT indicated for the prophylaxis of clean surgical wounds.